Tools

Numbers and bits

3 Colour converter · Floating-point inspector · Programmer's calculator

Colour converter Convert between HEX, RGB, HSL, HWB, OKLCH, OKLab, and CMYK; build tints, shades, and harmonies; check WCAG contrast.

Floating-point inspector See exactly how float64, float32, float16, bfloat16, TF32, the FP8, FP6, and FP4 formats used for AI, and the E8M0 scale store a number — and how block-scaled formats (OCP MX, NVIDIA NVFP4, NF4) build a tensor from tiny elements and shared scales.

Programmer's calculator Integer expressions with hex, binary, and octal; 8- to 128-bit words; signed or unsigned; bitwise operators, rotates, and a clickable bit grid; an n-bit overflow clock with signed and unsigned labels; and what n bits hold, with the KB versus KiB gap.

Data

10 Binary format decoder · CSV viewer · Data converter · Data wrangler …

Binary format decoder Decode MessagePack, CBOR (with tags), protobuf (with or without a .proto), BSON, and Python pickle opcodes into an annotated tree and hex view; encode JSON as MessagePack or CBOR.

CSV viewer Open CSV or TSV of any size in a fast scrolling table — sort, filter per column, search, column statistics, computed columns, and export to CSV, JSON, or Markdown.

Data converter Convert between JSON, YAML, CSV/TSV, XML, TOML, and query strings, and generate TypeScript, JSON Schema, Go, Rust, and Python types from JSON.

Data wrangler Clean and reshape tables with a recipe of steps — trim, retype, split, cluster near-duplicates, join, pivot, group — preview every step, then replay the recipe on new files or export it as SQL or pandas. DuckDB takes over for millions of rows.

Fake data generator Build a schema of typed fields and generate reproducible test data — people, addresses, orders, logs, sensor readings — as JSON, CSV, SQL, YAML, XML, or Markdown.

jq playground Real jq 1.8 in your browser — input, filter and output side by side, updating as you type, with the command-line flags, --arg and --argjson, over fifty example filters on sample data (a GitHub API response, a Kubernetes pod list, a JSON-lines log, a nested config), the output after every stage of the pipe, and the shell command to copy.

JSON workbench Validate, format, minify, sort, and repair JSON; browse and edit it as a tree; query with JSONPath; transform with JavaScript; and diff two documents.

Log parser Paste or drop logs (large files are streamed) — nginx/Apache, JSON lines, logfmt, syslog RFC 3164/5424, journald, Java with multi-line stack traces, Go zap/slog, Kubernetes CRI, CloudWatch — or write a grok pattern with the standard Logstash library; get field statistics, a zoomable time histogram, filter expressions, message templates (Drain), CSV/JSONL export, and the table in DuckDB lab or the data wrangler.

Python notebook A Jupyter-style Python notebook that runs entirely in your browser (Pyodide) — code and Markdown cells, one shared namespace, pandas tables and matplotlib figures inline, tracebacks, CSV upload, open and download .ipynb files, autosave, share links, and starter notebooks for pandas, plotting, linear algebra, SciPy statistics and simulation.

XML workbench Check XML is well-formed (with line and column), format or minify it, browse it as a tree, run XPath 1.0 queries with namespaces, convert to and from JSON, and preview XSLT transforms.

Encoding and text

8 Base64 and encoding converter · Data recipe · Protobuf and gRPC playground · Regular expression tester …

Base64 and encoding converter Convert text to and from Base64, Base64URL, hex, binary, decimal bytes, percent-encoding, HTML entities, and Unicode escapes — with a byte inspector and file support.

Data recipe Chain operations on text or a dropped file and see the output after every step — encodings, gzip and deflate, hashes and HMAC, AES-GCM/CBC/CTR, XOR and XOR brute force, ROT13, text and CSV/JSON operations, timestamps, entropy and a byte histogram — with “magic” that guesses the decoding steps.

Protobuf and gRPC playground Write a .proto, fill in a message with a generated form or as JSON, and see every byte of its encoding explained — tags, varints, zigzag, fixed widths, lengths, packed lists, maps, oneofs — next to its JSON size; gRPC and gRPC-Web framing; and a schema-evolution checker that says which changes between two versions break old or new code.

Regular expression tester Test JavaScript regular expressions live — highlighted matches, capture groups, replace and split previews, a plain-English explanation, and a pattern library.

Text diff Compare two texts by line, word, or character — side by side, inline, or as a unified patch — with whitespace and case options.

Text toolkit Case conversion, line sorting and de-duplication, counts, find and replace, escaping for JSON, HTML, SQL, CSV, and shell, slugs, lorem ipsum, and a whitespace visualiser.

Unicode inspector See every character's code point, name, category, script, UTF-8 and UTF-16 bytes, and escapes; split text into graphemes; compare NFC/NFD/NFKC/NFKD; find and strip invisible, bidi, and look-alike characters; and search characters by name.

URL encoder, decoder, and parser Percent-encode and decode text four ways, untangle double-encoded strings, and pull a URL apart into editable parts and query parameters.

Hashes and tokens

6 Certificate decoder · Classic cipher cracker · Hashes and checksums · JWT decoder and signer …

Certificate decoder Decode X.509 certificates and chains, CSRs, public and private keys, PKCS#7 bundles, and any DER as an ASN.1 tree; check chain order and expiry; and fingerprint SSH public keys. Everything stays in the browser.

Classic cipher cracker Encrypt, decrypt and crack the classic pencil-and-paper ciphers — Caesar, Atbash, affine, Vigenère, Beaufort, autokey, simple substitution, rail fence, columnar transposition and Playfair — with frequency, IoC, chi-squared and Kasiski analysis and a hand-solving workbench.

Hashes and checksums MD5, SHA-1, SHA-2, SHA-3, CRC-32, Adler-32, and xxHash for text or files of any size, plus HMAC and PBKDF2 — with hash comparison.

JWT decoder and signer Decode, inspect, verify, build, and sign JSON Web Tokens — HS, RS, PS, ES, and EdDSA — and generate test key pairs, all with WebCrypto.

SSH and PGP key inspector Paste or drop an SSH or OpenPGP key and see what it is — fingerprints and randomart exactly as ssh-keygen prints them, certificates, authorized_keys options, hashed known_hosts, OpenSSH and PEM private key headers, and OpenPGP packets with key IDs, expiry and warnings — or make a new SSH key pair in the browser.

UUIDs, IDs, and random values Generate and decode UUIDs (v1, v4, v5, v7), ULIDs, KSUIDs, nanoids, and Snowflake ids; make strong passwords and passphrases; random bytes, integers, and picks.

Time

3 Cron expression tool · Meeting planner · Time converter

Cron expression tool Explain, validate, and build cron expressions — Unix and Quartz/Spring syntax with L, W, # and macros — and see the next run times in any time zone.

Meeting planner Line up several time zones on a 24-hour grid with working hours shaded, find when everyone overlaps, get warned about clock changes, share a slot as text or ISO 8601, and convert a time between zones.

Time converter Convert epoch seconds, milliseconds, microseconds, and nanoseconds to and from ISO 8601, RFC 2822, and other formats in any time zone, with a world clock and date arithmetic.

Network

15 DHCP, ARP, NAT and routing · DNS lookup · Firewall packet tracer (iptables and nftables) · HTTP header analyser …

DHCP, ARP, NAT and routing A small network you can watch frame by frame: DHCP's Discover–Offer–Request–Ack with every option decoded, ARP and a learning switch, a ping through NAT and its translation table, port forwarding, longest-prefix match — plus OSPF-style flooding and Dijkstra, RIP counting to infinity, and BGP's decision process. Exports a .pcap.

DNS lookup Look up any DNS record over HTTPS through Cloudflare and Google, compare the two side by side, check DNSSEC, and decode SPF, DMARC, and DKIM.

Firewall packet tracer (iptables and nftables) Paste iptables-save or nft list ruleset output and a packet, and step it through the netfilter hooks in the kernel's order — every chain, every rule tested with the reason it matched or didn't, jumps, returns, policies, DNAT and MASQUERADE — to the final verdict; with Docker's and kube-proxy's chains explained.

HTTP header analyser Paste response headers from curl or DevTools to get a security grade, a line-by-line Content-Security-Policy and cookie audit, plain-English caching and CORS explanations, and a CSP builder.

HTTP request client A small Postman in the browser — collections, environments with {{variables}}, tests, and a collection runner; Postman, OpenAPI, and HAR import and export; status, timing, headers, and bodies; curl, fetch, or Python code.

IP subnet calculator IPv4 and IPv6 CIDR maths — network, broadcast, usable range, masks, special ranges, splitting, summarising, ranges to CIDRs, and reverse-DNS names.

My IP and connection Your public IPv4 and IPv6 addresses, whether IPv6 works, the Cloudflare data centre and TLS version you reach, your network owner, WebRTC candidates, and browser facts.

nginx and Caddy request router Paste an nginx config or a Caddyfile and a request, and step through what the server does with it — which server block and location win and why, rewrites, try_files, if, alias vs root, the proxy_pass trailing-slash rules, add_header inheritance — ending in the file served, the upstream URL or the redirect. Plus a table of requests checked against expected outcomes.

OpenAPI explorer Load any OpenAPI 3 or Swagger 2 description by URL, file, or paste; browse operations and schemas, fill in generated forms, send live requests, and check responses against the declared schemas.

Packet capture viewer (mini Wireshark) Open .pcap and .pcapng files in the browser: a Wireshark-style packet list, detail tree and hex view, display filters, TCP analysis (retransmissions, duplicate ACKs, zero windows), follow stream, conversations, endpoints, protocol hierarchy, IO graph, HTTP objects, and pcap, pcapng and HAR export.

Speed and latency test Measure download and upload speed, latency, jitter, and latency under load against Cloudflare's network — or time HTTP requests to any site.

TCP, simulated TCP you can watch: two hosts and a bottleneck router with a queue, every segment a labelled packet — the handshake and its options, sequence and ACK numbers, windows, delayed ACKs and Nagle, the RFC 6298 timer, fast retransmit, NewReno and SACK, Reno vs CUBIC vs BBR with cwnd plotted, bufferbloat, long fat pipes, fairness between two flows, FIN, TIME_WAIT and RST — exportable as a pcap.

TLS 1.3 and QUIC handshakes Step through TLS 1.3 (full, HelloRetryRequest, PSK resumption with 0-RTT), TLS 1.2 and QUIC handshakes message by message, with every byte built and every secret of the key schedule computed live with Web Crypto — and checked against the RFC 8448 and RFC 9001 test vectors.

User agent and IP inspector Parse any User-Agent string into browser, engine, OS, and device, read your browser's client hints, and convert IPv4/IPv6 addresses between every common notation.

WebSocket tester Connect to any WebSocket, send text, JSON, or binary frames, and watch a timestamped log with sizes, echo round-trip times, filtering, and export.

Search and relevance

11 Analyzer and inverted-index playground · Click models workbench · Data mining: frequent patterns and clustering · Elasticsearch, simulated …

Analyzer and inverted-index playground Build an Elasticsearch analyzer from char filters, a tokenizer and token filters and watch the token stream change stage by stage — terms, positions, offsets, types and position lengths, drawn as a token graph — then index documents to see the postings, field-length norms and phrase/slop matching, and copy the _analyze request and index settings.

Click models workbench Load a query and click log (or simulate one from known relevance and a known user), see CTR by rank, abandonment and reformulations, fit the click models of Chuklin, Markov & de Rijke — PBM, cascade, DCM, UBM, SDBN, DBN — checked against PyClick, correct for position bias with propensities from PBM or swap experiments, and compare interleaving with A/B testing.

Data mining: frequent patterns and clustering Frequent itemsets with Apriori (level by level, pruning shown) and FP-Growth (the FP-tree drawn), association rules with support, confidence, lift, leverage and conviction; and clustering — k-means step by step with k-means++, elbow and silhouette, DBSCAN with its k-distance plot, hierarchical clustering with a dendrogram — on points you edit or a CSV, checked against mlxtend, scikit-learn and scipy.

Elasticsearch, simulated An animated, step-by-step Elasticsearch (and OpenSearch) cluster in your browser: murmur3 routing, primaries and replicas, the indexing buffer, translog, refresh, flush and segment merging inside every shard, query-then-fetch search, node failures, master elections, split brain and shard sizing — with guided scenarios and a REST console.

Near-duplicate detection Find near-duplicate documents: character or word shingles, exact Jaccard, seeded MinHash signatures, LSH banding with its S-curve and a (b, r) tuner, 64-bit SimHash with the permuted-table search, precision and recall against an exact similarity join, and clusters — 10,000+ documents in a Web Worker.

Postings lab Inside an inverted index: build one from documents and look at docIDs, frequencies and positions; compress the postings with VByte, Elias γ/δ, Golomb/Rice, Simple-9/16, FOR and PForDelta blocks of 128, Lucene's PForUtil and Roaring bitmaps (bits per posting, bit by bit); intersect with skips and galloping; and step through MaxScore, WAND and Block-Max WAND against exhaustive BM25.

Query DSL builder and explainer Build Elasticsearch and OpenSearch queries in a form or as JSON — each edits the other — and see them explained in plain English (query vs filter context, minimum_should_match, the Lucene query they become), linted for slow or surprising patterns, and run against a sample index in your browser with hits, scores, explanations, highlights and aggregations; optionally send them read-only to your own cluster.

Ranking metrics workbench Paste TREC qrels and runs (or CSV) and get P@k, recall@k, MAP, MRR, nDCG@k with linear and exponential gain, ERR and R-precision per query — checked against trec_eval and gdeval — then compare two rankers with paired t, Wilcoxon, randomisation and bootstrap tests, and simulate team-draft interleaving.

Relevance and scoring explainer See why documents rank where they do: BM25 term by term like Elasticsearch's _explain, with k1 and b sliders that re-rank live, classic TF-IDF side by side, multi-field strategies and boosts, function_score (field_value_factor, decay curves, a recency script), and hybrid lexical + vector ranking with reciprocal rank fusion or a normalised linear blend.

String matching and fuzzy search Edit distances with the dynamic-programming table filled cell by cell (Levenshtein, OSA vs true Damerau, LCS, Hamming), Jaro–Winkler, Levenshtein automata as Lucene's FuzzyQuery builds them and walks the term dictionary, Soundex, Metaphone, Double Metaphone and NYSIIS, pg_trgm trigram similarity, and a Norvig spelling corrector.

Vector search, simulated Approximate nearest-neighbour search you can watch: build and search HNSW layer by layer, train k-means and probe IVF cells, quantize with PQ, int8 and binary codes, compare L2, cosine and dot product, and benchmark recall against work and memory in a Web Worker.

Distributed systems

11 Cache simulator · Capacity and queueing planner · Clocks, CRDTs and gossip · Consistency models lab …

Cache simulator Every major eviction policy — LRU, LFU, FIFO, CLOCK, ARC, 2Q, W-TinyLFU, S3-FIFO — against Belady's optimum on Zipf, loop, scan and shifting workloads or your own trace; hit-ratio curves for all of them at once, a step-through of each policy's internal state, write policies, cache stampede fixes (singleflight, jitter, XFetch, stale-while-revalidate) and hot-key and two-tier maths.

Capacity and queueing planner Queueing maths for capacity planning: Little's law, M/M/1, M/D/1, M/G/1 and Kingman, M/M/c with Erlang C and exact percentiles, the utilisation-versus-latency knee, the tail at scale of fan-out requests, hedged and tied requests, a discrete-event simulator that checks the formulas, and a planner that turns a p99 target into a server count.

Clocks, CRDTs and gossip Time and agreement without coordination: space-time diagrams with Lamport, vector and hybrid logical clocks (skewed and drifting physical clocks, last-writer-wins gone wrong, causal broadcast); CRDTs from G-Counter to OR-Set and a collaborative RGA text editor across three replicas; and SWIM failure detection and epidemic gossip, animated.

Consistency models lab Watch a three-region replicated store at Cosmos DB's five consistency levels — strong, bounded staleness, session, consistent prefix, eventual — with stale and out-of-order reads, latency and availability counted as you cut regions off or fail them; the four session guarantees and causality, each broken and fixed; a linearizability and sequential-consistency checker for your own histories; and a clickable map of the models.

Load balancing and resilience, simulated An animated, step-by-step fleet of servers behind a load balancer: round robin, least outstanding, power of two choices, peak-EWMA and consistent hashing with bounded loads; then timeouts, retries with jitter and budgets, retry storms and metastable failure, circuit breakers, hedged requests, load shedding and adaptive concurrency limits — with latency, throughput and error charts over time.

Offline-first sync and replication How offline-first apps sync, animated: CouchDB/PouchDB-style replication between a phone, a laptop and a server that go offline — revision trees, the changes feed, checkpoints, _revs_diff and _bulk_docs, conflicts and the deterministic winning revision, three ways to resolve them, compaction and _revs_limit's false conflicts — against a Firestore-style single-leader cache with pending writes, server timestamps and rolled-back writes.

Partitioning and replication Where keys live and how copies stay in step: consistent hashing with virtual nodes, rendezvous, jump hash and Maglev with animated key movement; an animated Dynamo-style store with preference lists, N/R/W quorums, sloppy quorums and hinted handoff, read repair, vector-clock siblings and Merkle-tree anti-entropy; and the latency and staleness of partial quorums.

Probabilistic data structures Bloom, counting Bloom and cuckoo filters, the Count-Min sketch with conservative update and heavy hitters, HyperLogLog (original, HLL++ sparse and Ertl's estimator), the t-digest and reservoir sampling — each fed by a live seeded stream, drawn from the inside, with accuracy-vs-memory charts against the formulas.

Raft and Paxos, simulated Consensus you can watch: Raft servers with terms, votes, logs and commit indexes exchanging labelled RequestVote and AppendEntries messages — elections, split votes, replication, crashes, log repair, partitions, the paper's Figure 8, membership changes, ReadIndex and lease reads, snapshots — plus Basic and Multi-Paxos and a randomised safety torture test.

Storage engines: LSM-tree vs B-tree, simulated A B+tree and an LSM-tree side by side in your browser, fed the same operations: page splits and merges, the WAL and buffer pool, memtable flushes, leveled, size-tiered and lazy-leveling compaction, Bloom filters, fence pointers and tombstones — with write, read and space amplification counted as you watch, guided scenarios and the textbook cost models.

Transactions across services, simulated Atomic commitment and its alternatives, animated: two-phase commit with forced log writes, in-doubt participants and a blocking coordinator crash, presumed abort and commit, three-phase commit failing under a partition, orchestrated and choreographed sagas with compensations and a semantic lock, and the dual-write problem fixed by a transactional outbox and an idempotent consumer.

Cloud

7 AWS architecture builder · AWS IAM policy evaluator · Data-lake browser · EventBridge pattern tester …

AWS architecture builder Draw an AWS architecture on an interactive diagram — VPCs, subnets and 40 services, from web tiers to data lakes, warehouses, stream processing and search — configure each service, see a rough monthly cost, and download a TypeScript AWS CDK app that synthesises.

AWS IAM policy evaluator Paste IAM policies — identity-based, resource-based, permissions boundaries, session policies, SCPs and RCPs — and a request, and see Allow, explicit deny or implicit deny with a trace of every statement and every step of AWS’s evaluation logic; plus a policy linter and an ARN parser.

Data-lake browser Browse and query object stores and HDFS from the browser — S3, MinIO, R2, B2, Wasabi, GCS, Azure Blob and WebHDFS/HttpFS: buckets and folders, uploads with resumable multipart, Range downloads, presigned URLs, Parquet/ORC/Avro schema and row-group statistics, DuckDB SQL over files, HDFS block locations, bucket CORS/policy/lifecycle generators, and the aws/mc/gcloud/az/hdfs command and curl for every action.

EventBridge pattern tester Test EventBridge event patterns against events and see why each field matches or not — exact values, prefix and suffix (with equals-ignore-case), every anything-but form, numeric ranges, exists, IP CIDR, wildcards, $or and array semantics, following the AWS content-filtering rules — plus input transformers (InputPathsMap and InputTemplate) and a library of sample events.

GCP architecture builder Draw a Google Cloud architecture on an interactive diagram — a project, its region and VPC network, and 37 mainstream services, including a big-data platform (warehouse, batch and stream processing) and a search and caching service tier — configure each service, see a rough monthly cost, and download Terraform that passes terraform validate.

Serverless sizing: Lambda, SQS, Kinesis, SNS and API Gateway Size and price a serverless design — Lambda cost by memory, duration, requests and architecture (with the free tier, INIT billing and provisioned concurrency), concurrency from rate × duration against the account and scaling limits, cold-start factors, SQS batch and visibility-timeout checks with FIFO limits, Kinesis shards and on-demand against provisioned, SNS fan-out and API Gateway REST against HTTP — every price dated and sourced.

Step Functions workbench Paste an Amazon States Language definition and see it drawn as a graph, checked for common mistakes, and run step by step with mocked Task results — every InputPath, Parameters, ResultSelector, ResultPath and OutputPath (or JSONata Arguments, Output and Assign) shown with the data it produced, intrinsic functions, variables, Retry with back-off, Catch, timeouts, Parallel and inline or distributed Map.

Containers and Kubernetes

13 Compose visualiser · Container dashboard · Container image layers · docker run builder and explainer …

Compose visualiser Paste a docker-compose.yml and see its services, networks, volumes, ports and depends_on as a diagram, the start-up order, the effective config after ${VAR} interpolation and profiles, and a kompose-style Kubernetes translation.

Container dashboard A read-only dashboard for your own Docker and Kubernetes through a small local relay: containers, images, volumes and networks with live stats and logs; namespaces, workloads with rollout status, pods, services and endpoints, nodes, events, YAML, and a topology diagram — with every request copyable as curl, docker or kubectl.

Container image layers Open a docker save tar or an OCI image layout and see each layer with its Dockerfile instruction and size, the merged file tree with what every layer added, changed and deleted, wasted space and dive's efficiency score, the config, the platforms in the index, every digest checked — and the packages inside, handed to the SBOM viewer.

docker run builder and explainer Build a docker run command from a form, or paste one and get every flag explained — ports, mounts, env, network, limits, healthcheck, security — with warnings, and convert it to a Compose service and back.

Dockerfile explainer and linter Paste a Dockerfile and see what every instruction does, which ones make layers, what a change rebuilds, how the stages connect and roughly how big the image is — with hadolint-style lints and one-click fixes.

Helm and Kustomize renderer Render a Helm chart or a Kustomize overlay to plain YAML in the browser — with Helm's and Kustomize's own code compiled to WebAssembly — and see which values file or --set won each key, errors pointing at the template line, NOTES.txt, and what differs between two overlays.

How containers work, simulated An animated, step-by-step Linux host running Docker in your browser: docker run through dockerd, containerd and runc to clone(); namespaces, cgroups and the OOM killer; overlayfs copy-up and whiteouts; the build cache; pulling by digest from a registry; the bridge, veths, DNS and NAT; volumes; and the capabilities, seccomp and user namespaces that keep a container in — with a terminal that drives the same diagram.

kubectl helper: commands, selectors, JSONPath, RBAC Build kubectl commands with every flag explained; test label selectors against pods; try kubectl's JSONPath and custom-columns output on sample or pasted objects; and paste Roles and bindings to ask "can this user do that?", with the rule that grants it and a permissions matrix.

Kubernetes manifest builder and explainer Build Kubernetes manifests from forms — Deployments to NetworkPolicies — with live YAML, checks across the whole bundle, kubectl-explain docs for every field, a CPU and memory unit converter with the QoS class your requests and limits produce, probe timelines and a CronJob schedule explainer.

Kubernetes NetworkPolicy and Pod Security checker Paste NetworkPolicies, pods and namespaces (or kubectl get -o yaml output) and ask whether one pod can reach another on a port, with the policies that allow it or the reason it's blocked; a colour-coded pod × pod matrix, a lint, a policy builder, and a Pod Security Standards checker that lists every failing field and its fix.

Kubernetes scheduling explainer Paste your nodes and a pod or Deployment and see which nodes it can run on and why — every scheduler filter per node, the scores and weights that pick the winner, the FailedScheduling message, preemption victims, and N replicas placed one after another — checked against the real kube-scheduler v1.36.

Kubernetes, simulated An animated Kubernetes cluster in your browser: kubectl, the API server and etcd, controllers reconciling desired and actual state, the scheduler's filters and scores, kubelets pulling images and running probes, kube-proxy and Services, the HPA, StatefulSets, Jobs, drains and PodDisruptionBudgets — with guided scenarios and a pretend kubectl.

SBOM and vulnerability report viewer Open a CycloneDX or SPDX SBOM, or a Trivy, Grype or OSV-Scanner report, and see the components by ecosystem with purls and licences (SPDX expressions parsed, copyleft flagged), the dependency graph, vulnerabilities by severity with fixed-in versions and "upgrade X to Y fixes N" suggestions — and what changed between two SBOMs.

Databases and streaming

32 Cassandra lab · Connection pool sizing · Distributed patterns on Redis · DuckDB analytics lab …

Cassandra lab A Cassandra data-modelling lab and CQL client: a cqlsh-like console on a built-in Cassandra node (CQL, TTLs, tombstones, SSTables, lightweight transactions), a query-first checker that says which queries a table supports and why, partition sizes and hot partitions, the token ring with vnodes and replica placement, consistency levels with replica responses — and a native-protocol client for your own Cassandra through the gitwebsite app.

Connection pool sizing How big should the database connection pool be? Little's law and Erlang C from your request rate and connection hold time, the PostgreSQL wiki's cores × 2 + spindles explained, every instance's pool against max_connections (RDS defaults included), a simulation of a pool too small and too large, and HikariCP's settings with maxLifetime and keepalive worked out from the idle limits on your network path.

Distributed patterns on Redis A catalogue of 75 distributed patterns built on Redis — locks, leases and fencing, transactions and Lua, queues and streams, notification, rate limiting, caching, idempotency, counting, data structures, service coordination and cluster-aware design — each with its guarantees, its Lua, its failure modes and 185 labs you can step through: clients racing on a Redis in the page, real Lua included, without the pattern and with it, and on your own server. Plus Redis Cluster and Sentinel, animated.

DuckDB analytics lab Real DuckDB in your browser with a console, results grid, plan trees for EXPLAIN ANALYZE, quick charts and CSV/Parquet export — sample datasets, your own CSV/Parquet/JSON files read locally, and twelve guided labs: window functions, QUALIFY, PIVOT, ASOF joins, ROLLUP/CUBE, nested types, regex, Parquet metadata and columnar storage.

DynamoDB single-table modeller Design a DynamoDB single table — entities with key templates, GSIs and LSIs — see its items grouped by partition, check every access pattern (which GetItem or Query serves it, on which index, and how much it reads to return what), estimate capacity and on-demand against provisioned cost, and export to NoSQL Workbench, CloudFormation or CDK; with a DynamoDB engine in the page and a client for DynamoDB Local.

Explain plan Paste PostgreSQL EXPLAIN (JSON or the usual text) or MySQL EXPLAIN ANALYZE / FORMAT=JSON and see the plan as a tree with each node's own time, a flame chart and a table of hotspots, the problems found — row misestimates, sorts and hashes spilling to disk, big filtered scans, missing join indexes, JIT overhead, foreign-key triggers — with advice for each, and two plans compared side by side.

Flink, simulated An animated Flink job in your browser: Kafka partitions feeding chained operators, keyBy through key groups, event-time windows driven by watermarks, keyed state on HashMap or RocksDB, checkpoint barriers (aligned and unaligned), failure and recovery, a two-phase-commit Kafka sink, backpressure and rescaling from a savepoint — with guided scenarios, a key-group calculator and a window explorer.

Graph database playground Write Cypher against sample graphs — movies, a social network, a metro — in an engine that runs in the page (MATCH with variable-length paths and shortestPath, WITH, aggregation, CREATE/MERGE/SET/DELETE, EXPLAIN and PROFILE), see results as a force-directed graph, a table or cypher-shell text, and run the same queries on a real Neo4j over Bolt.

Isolation lab Two or three SQL sessions side by side: step through an interleaving and watch what PostgreSQL or MySQL InnoDB does at each isolation level — results, which statement blocks on which lock, deadlocks, serialization failures (40001 / 40P01) and the final table — with the classic anomalies, their fixes and the Hermitage tests built in, or the same steps on a real Postgres server.

Java GC log analyser Read a JVM GC log — unified -Xlog:gc* for G1, ZGC (generational or not), Shenandoah, Parallel and Serial, or a JDK 8 PrintGCDetails log — and get a pause timeline, heap before and after, allocation and promotion rates, pause percentiles, throughput, full GCs and failures flagged, and tuning hints in plain words.

Java thread dump analyser Paste jstack, jcmd Thread.print, kill -3 or Thread.dump_to_file (text or JSON, with virtual threads) output: threads grouped by state and identical stack, deadlocks and a lock graph, thread pools, hot frames, CPU per thread, and a comparison of dumps taken seconds apart to find stuck threads.

JVM memory planner for containers How a Java process fills a container's memory limit — heap, metaspace, code cache, thread stacks, direct buffers, GC structures and native memory — with the heap the JVM picks by itself on JDK 17, 21, 25 and 27, the flags that fit, OOMKilled versus OutOfMemoryError, and NMT output to fill it in.

Kafka client Work with a real Kafka cluster from the browser through a REST proxy (Confluent REST Proxy or Redpanda): brokers and configs, topics with partitions, ISR and offsets, produce single records or batches, consume by group or partition with live tail, consumer group lag and offset resets — and a log of every HTTP call, with copy as curl.

Kafka, simulated An animated, step-by-step Kafka cluster in your browser: partitions as replicated logs, the ISR and high watermark, acks and min.insync.replicas, broker failures and KRaft leader elections (clean and unclean), idempotence and transactions, consumer-group rebalances, compaction and retention — with guided scenarios.

MongoDB playground A mongosh-like console on a MongoDB that runs in your browser — with sample data, an aggregation pipeline builder that previews every stage, explain plans drawn as a tree (COLLSCAN vs IXSCAN), schema inference and $jsonSchema validators, a reference with runnable examples — and a real-server mode that speaks MongoDB's wire protocol through the gitwebsite app.

MongoDB replica sets and sharding, simulated An animated MongoDB cluster in your browser: a replica set with its oplogs, elections in terms, write concern and the rollback of acknowledged w:1 writes, read concern and read preference with maxStalenessSeconds; a sharded cluster with mongos, config servers, ranges, hashed and ranged keys, zones, the balancer and jumbo ranges; a query-targeting checker and a shard-key evaluator.

NoSQL capacity and cost Size NoSQL deployments with the working shown: Cassandra and ScyllaDB nodes from rows, replication and compaction headroom, with node-replacement and repair times; Redis memory per key by encoding (listpack, intset, hashtable, skiplist) with fragmentation, replication buffers and an eviction policy; MongoDB working set, WiredTiger cache and oplog window; Azure Cosmos DB request units, partitions and cost; and a Zipf hot-partition checker.

NoSQL data modelling Model one application four ways — document (embed or reference, with the subset, bucket, extended-reference, computed and outlier patterns), wide column (one table per query), key-value (keys and hand-made indexes) and graph — and see for each which access patterns are one read, several or scatter-gather, how many copies every write touches and what can go out of step; then a "Which database?" questionnaire with a reasoned shortlist and a CAP/PACELC explainer, and exports as CQL, MongoDB $jsonSchema, Cypher and JSON.

OpenTelemetry trace viewer Open a distributed trace as OTLP/JSON, a Jaeger export or Zipkin v2 JSON and read it as a waterfall with events and errors, a service map, the critical path and self time per service — flag and adjust clock skew, compare two traces span by span, and convert between the formats, all in the browser.

Postgres playground Real PostgreSQL 18 in your browser (PGlite) with a psql-like console, twenty runnable labs for the distributed patterns Postgres does well — SKIP LOCKED queues, advisory-lock mutexes, leases with fencing tokens, leader election, LISTEN/NOTIFY, outbox, idempotency keys, rate limits — an animated model of concurrent sessions, and a real-server mode that races sessions on your own Postgres.

PromQL and LogQL playground Write PromQL and LogQL against four hours of generated metrics and logs — counters with resets, histograms, a failing instance, a target that goes down — see the result as a graph or table, and walk through any query step by step, down to the arithmetic of rate()'s extrapolation and histogram_quantile()'s interpolation.

RabbitMQ, simulated An animated RabbitMQ broker in your browser: producers, exchanges (direct, fanout, topic, headers, default), bindings, classic and quorum queues and consumers, with every publish, route, delivery, ack, confirm and dead-lettering drawn as it happens — prefetch, requeues, TTL, max-length, priorities, DLX retry with backoff, poison messages and RPC, in guided scenarios or a topology you build.

Redis client A redis-cli in the browser with a built-in Redis to practise on, Lua scripts and functions, a reference for 255 commands with runnable examples, per-connection history, a key browser, pub/sub and stream viewers — and connections to real Redis servers over a REST gateway or a WebSocket bridge.

Row key design Build a row key from parts — fields, reversed timestamps, salts, hash prefixes, padding, separators — run a workload against Bigtable, HBase, Cassandra or DynamoDB, and see where the writes land over time (region splits included), which queries become one range scan and which a fan-out or scatter-gather, and what the key costs in bytes.

Schema diff Paste two SQL schemas (PostgreSQL or MySQL, hand-written or from pg_dump / mysqldump) and get the migration from one to the other as SQL, Flyway versioned files or a Liquibase changelog (YAML or XML), with warnings for the changes that rewrite or lock tables — by database version — and an ER diagram of what changed.

Server config builders Build and explain nginx, Caddy, systemd and SSH configs — reverse proxies with Mozilla TLS settings, WebSockets and rate limits (with a limit_req simulation), static sites, hardened systemd services and timers with next run times and an exposure estimate, and ssh_config hosts and tunnels with a diagram — or paste your own and have each line explained and checked.

Spark, simulated An animated Spark application in your browser: a DataFrame or SQL program becomes a logical plan, Catalyst rewrites it, the planner picks joins and inserts shuffles, the DAG scheduler cuts stages and runs tasks on executors with real memory regions — with guided scenarios on partitions, skew, joins, AQE, caching, spills and failures, an executor sizing calculator and an EXPLAIN reader.

SPARQL and RDF playground A real SPARQL 1.1 engine (Oxigraph, in WebAssembly) in the page — load Turtle, TriG, N-Triples or JSON-LD, run SELECT, CONSTRUCT, ASK, DESCRIBE and updates, see results as a table, as Turtle or as a graph drawing, work through labs on property paths, aggregates, named graphs and RDFS inference by rules, or query Wikidata.

Spring Boot inspector Paste Spring Boot Actuator output and read it: why each auto-configuration did or didn't apply, the bean dependency graph, which property source wins for every key, bound @ConfigurationProperties, the endpoint table, metrics and health. Plus a properties ↔ YAML converter with profiles, a checker for common keys, and every relaxed-binding form of a property name.

SQLite internals Real SQLite in your browser with a console, and what is underneath: the database file decoded page by page (header, b-tree pages, cell pointers, cells and records, overflow and freelist pages), a b-tree diagram for any table or index, VDBE bytecode annotated opcode by opcode, query plans as trees, the pages each statement writes — and eleven labs from rowid tables to WAL.

Terraform plan visualiser Open the JSON of a Terraform or OpenTofu plan and see what it will create, change, replace and destroy — with why each replacement is forced, warnings for destroyed data stores, sensitive values masked, the attribute diffs as terraform plan prints them, and the dependency graph from the configuration's references.

Time-series database lab Inside a time-series database: validate InfluxDB line protocol and Prometheus exposition text and see the series keys; watch Gorilla, Prometheus XOR/XOR2 and InfluxDB TSM compression bit by bit on your data (byte-identical to Prometheus's and InfluxDB's own encoders); estimate cardinality and memory; downsample counters correctly; size retention tiers; and watch Prometheus cut and compact blocks.

Linux and macOS

10 Binary inspector: Mach-O, ELF and PE · launchd jobs · Linux shell playground · Linux triage …

Binary inspector: Mach-O, ELF and PE Drop an executable or library — Mach-O (thin or universal), ELF or Windows PE — and see its load commands or headers, libraries and run paths, symbols demangled, fixups, the code signature with entitlements and requirements, a checksec-style hardening list, Go build info, Rust crates, strings, a hex view of any section and a size treemap.

launchd jobs Build a launchd job (LaunchAgent or LaunchDaemon) from a form, or paste one to have it explained and checked; turn crontab lines into StartCalendarInterval, see the next run times and what happens if the Mac sleeps through one, and get the launchctl bootstrap/bootout/enable/kickstart/print commands.

Linux shell playground A real Linux booted in the page (a small kernel and BusyBox in the v86 x86 emulator) with a terminal, sample logs, CSVs and a config tree in your home directory, and 26 exercises — text pipelines, find and xargs, redirection, permissions, processes and signals, environment variables, loops — that check your answer.

Linux triage Paste the output of uptime, dmesg, vmstat, mpstat, pidstat, iostat, free, sar, top, /proc/meminfo, /proc/pressure, ss and cgroup files — several at once, in any order — and get a reading in the style of Brendan Gregg's 60-second checklist and the USE method: what each column means, what is abnormal, what to run next. Plus exit codes and signals (137 OOM-kill vs SIGKILL, 143) for Docker and Kubernetes.

Property lists and defaults Open any property list — XML, binary (bplist00, every type including UIDs and dates), old-style OpenStep, `defaults read` output or JSON — edit it as a tree and get the plutil and defaults commands for each change, convert it byte-for-byte the way plutil does, take a binary plist apart, and browse a curated catalogue of defaults write tweaks with read and undo commands.

Shell command explainer Paste a command line or a script and see it taken apart — pipes, redirections, && and ||, subshells, loops, quoting, variables, substitutions, globs and here-documents — with every option of 170 common commands explained, warnings for dangerous patterns such as rm -rf $DIR/ and curl | sh, and ShellCheck-style notes on common mistakes.

Shell prompt builder Build a zsh PROMPT/RPROMPT and a bash PS1 from blocks — user, host, directory, git branch and state, exit status, time, venv — with a live preview in several terminal colour schemes; paste any prompt to see it expanded and explained escape by escape; and paste zprof or a timed xtrace log to find what makes zsh slow to start.

strace viewer Paste strace output — with or without -f, -tt/-ttt/-r, -T, -y/-yy, unfinished/resumed pairs, signals, -c tables — or macOS dtruss output, and get a per-thread timeline, a summary that matches strace -c, the slowest calls, errors grouped (path probing, EAGAIN loops), files with bytes read and written, connections and DNS lookups decoded from the buffers, the process tree with argv, and hints.

tmux lab Learn tmux by doing in a simulated tmux in the page — the real default keys, splits, layouts, zoom, windows, sessions, copy mode in vi or emacs keys, the command prompt, detach and attach — plus a .tmux.conf builder that explains every line, a live status-line preview, a layout-string decoder and encoder with the checksum, a searchable cheat sheet and how cmux compares.

Unix permissions calculator Convert between the permission checkboxes, octal (755), and symbolic (rwxr-xr-x) modes — with setuid, setgid, sticky, umask, ls -l parsing, and ready-to-run chmod commands.

Interview prep

2 Coding interviews · System design interviews

Coding interviews A coding-interview trainer: thirty-three patterns with the signals that give them away, animated step-throughs and templates in Python, JavaScript, Java and Go; a clickable pattern map from problem signals to patterns; about 160 original problems with staged hints, reference solutions you can step through line by line, and hidden tests, run in your browser in JavaScript or Python with a scaling check; a visualiser your own code can draw with; a which-pattern quiz; a 45-minute mock interview with a rubric and history; a STAR story bank for the behavioural round; and per-pattern mastery.

System design interviews Practise big-tech style system design interviews: a paced 45- or 60-minute framework with a mock interviewer, random questions and a self-scoring rubric, a back-of-the-envelope estimator, 38 reference architectures (likes, web search, webhooks, group chat, Kafka- and Dynamo-style stores, maps, a matching engine and more) as clickable diagrams with model deep-dive answers and interview cards, a live simulation of each one you can overload and break, a searchable question bank with a compare view, runnable building blocks (rate limiters, consistent hashing, Snowflake IDs, Bloom filters, fencing tokens, the outbox pattern and more) with Python, Go and Java versions, and trade-off cards.

Formatting and reference

34 Big-O explorer and benchmark · Bundle analyzer · Code beautifier and minifier · Compose, Kubernetes, and cron checker …

Big-O explorer and benchmark Compare growth curves, see how big an input fits a time budget, benchmark your own JavaScript to find its complexity class, look things up in a colour-coded Big-O cheat sheet, watch sorting algorithms run, and see where the costs come from: Fibonacci call trees, recursion trees, binary-search halving, and amortised appends — and why attention is O(N²) in context length, what an SSM's O(N) buys, and what a KV cache saves. Then revise for interviews: name the complexity of code snippets, drill data-structure operation costs, and solve recurrences with the master theorem.

Bundle analyzer Drop webpack stats, Vite/Rollup visualizer data, an esbuild metafile or your minified .js with its .map and see what is in the bundle — a zoomable treemap, modules and packages by size, duplicated packages, why each module is included, the chunks, and what changed between two builds.

Code beautifier and minifier Beautify or minify JavaScript, TypeScript, JSON, CSS/SCSS/LESS, HTML, and XML, with indentation, wrapping, and brace-style options and before/after sizes.

Compose, Kubernetes, and cron checker Check docker-compose.yml and Kubernetes manifests for mistakes that break deployments — unknown keys, bad references, port clashes, selector mismatches, removed API versions, invalid quantities — and convert crontabs to systemd timers.

Concurrency lab Step through concurrent programs one operation at a time, rewind, and try other interleavings: Go goroutines, channels, select, WaitGroup, Mutex and context (with a race detector, deadlocks and leaks), async Rust futures on a tokio-like executor, Java virtual threads on carriers with pinning, executors and CompletableFuture, and the JavaScript event loop — plus a runner that shows the real order of your own JS snippet.

CSS playground Generate gradients, layered box shadows, and border radii; try flexbox and grid settings live; work out clamp() fluid type; shape cubic-bezier easings with a running animation; and convert between px, rem, em, vw, and pt.

Dependency tree analyser Paste mvn dependency:tree, gradle dependencies, go mod graph or cargo tree output, or drop a package-lock.json, pnpm-lock.yaml, yarn.lock or Cargo.lock, and see the tree, why each package is there, which version won each conflict and why, duplicates, depth and weight, licences, and (if you ask) known vulnerabilities from OSV.dev.

Diagram and AsciiDoc studio Live Graphviz (compiled to WebAssembly) and Mermaid editors, plus an AsciiDoc preview that renders [graphviz] and [mermaid] blocks inline and checks a gitwebsite post header — export SVG, PNG, or HTML.

Documentation linter Lint Markdown with the real markdownlint rules (MD001–MD060, your .markdownlint.json) and AsciiDoc with structure checks that match Asciidoctor's warnings, with quick fixes — plus a table formatter for Markdown, AsciiDoc, CSV and TSV.

Flame graph and profile viewer Open a CPU, heap or lock profile — Go pprof, collapsed stacks from async-profiler, perf or cargo flamegraph, JDK Flight Recorder, a Node/Chrome .cpuprofile, speedscope or perf script — and read it as a flame graph or icicle with search, a top table, callers and callees, and a red/blue differential against a baseline, all in the browser.

Git client A git client in the browser: open a local repository (read-only unless you switch on write mode), see the commit graph, diffs, blame, file history, status and stashes; browse GitHub and GitLab repositories, pull requests and issues; clone over HTTPS through a relay you run.

Git helper Searchable "how do I…" git recipes with safety notes, a .gitignore generator with a path tester, a Conventional Commits builder and linter, and .gitattributes and branch-name generators.

Git, visualised Learn git by doing: a terminal that runs real git commands against a faithful in-browser git (real SHA-1 object ids), with an animated commit graph, the three trees, the object database, a 34-lesson course with automatic goal checks, and disaster-recovery scenarios.

GitHub Actions workflow explainer Paste a GitHub Actions workflow: the job graph with a what-if-this-fails simulator, every matrix job after include/exclude, triggers with a branch/tag/path filter tester and next cron runs, a ${{ }} expression evaluator with an editable context, GITHUB_TOKEN permissions per job, concurrency groups, and actionlint's checks plus security checks.

Grammar and parser playground Write a PEG grammar, parse input with it live, and inspect the result tree, JSON, tokens, and rule cross-references — then download the generated parser. Or see one expression parsed under five precedence conventions — PEMDAS, implied multiplication, Python, C and Excel — as trees.

GraphQL playground A GraphQL server in your browser — write a schema in SDL and resolvers in JavaScript over sample data (a blog, a library, a shop), query it with hints from the schema, and watch every resolver call and database query on a timeline, which is how the N+1 problem shows itself and DataLoader fixes it. Also sends queries to real endpoints.

HTTP reference Searchable HTTP status codes, headers, and methods; a REST API design guide; a MIME type table; a CORS cheat sheet; and a Cache-Control explainer.

Java class file and JAR inspector Drop a .class or .jar and read it like javap -v — class version, constant pool, fields, methods with full bytecode, every attribute — plus the JAR's manifest, module-info, multi-release versions, Spring Boot nested jars and duplicate classes.

JSON → types Paste JSON samples (or a JSON Schema) and get TypeScript, Zod, Java records with Jackson (or Lombok classes), Kotlin, Go structs, Rust serde, Python pydantic or dataclasses, protobuf, or JSON Schema — merging samples to find optional fields, nulls, unions, enums, dates, UUIDs, maps and tagged unions.

Language sandbox Write and run code in 29 languages — JavaScript, TypeScript, Python, Java, Kotlin, C, C++, Rust, Go, R, PHP, Perl, Ruby, Lua, OCaml, Fortran, Clojure, Scheme, Prolog, BQN, Forth, BASIC, SQLite, DuckDB, HTML, p5.js, GLSL, Brainfuck and Befunge — and share it as a link.

Latency numbers every programmer should know Jeff Dean's and Peter Norvig's latency tables, Colin Scott's year-by-year model from 1990 to 2030, the famous squares diagram, a human-scale view, comparisons, back-of-the-envelope calculators, and AI-hardware latencies (HBM, NVLink, InfiniBand, CXL) with KV-cache hand-off and checkpoint estimates.

Makefile explainer Paste a GNU Makefile and a list of files with their times: see what make -n would run and why, in order, with the recipes expanded; a dependency graph where you can touch a file; every rule and variable explained; and lints for missing .PHONY, spaces instead of tabs, $VAR in recipes and recursive-make pitfalls.

Markdown and AsciiDoc previewer Live side-by-side preview of Markdown (GitHub-flavoured) and AsciiDoc, with a table of contents, word count, HTML export, and HTML → Markdown conversion.

Markdown ↔ AsciiDoc converter Convert Markdown (GitHub-flavoured, with alerts, footnotes and front matter) to AsciiDoc and back, see both rendered side by side, and get a report of everything that had to be approximated.

Maven and Gradle build files Paste POMs (with their parents and BOMs) and get the effective POM with where every value came from, profiles you can switch, BOM import order, the phases and plugin goals a command like mvn clean verify runs, and lints. Read build.gradle(.kts) with its version catalog and see which classpaths each dependency lands on. Convert POM ↔ Gradle and Groovy ↔ Kotlin DSL, and compare Maven and Gradle version ordering and conflict rules.

Memory layout: Go, Rust, C and Java Paste a Go struct, Rust struct or enum, C struct or Java class and see every byte — fields, padding, object headers, enum tags and niches — on 64-bit and 32-bit targets, with Go's fieldalignment reordering, rustc's own field order, HotSpot's field packing, and a gallery of runtime internals (slice and interface headers, Vec, Box, Rc, fat pointers, String, HashMap.Node).

Policy playground: Rego and CEL Write policies in Rego and CEL and test them against JSON inputs in the browser — a Rego interpreter with a trace of which rules fired and why the others didn't, real CEL with type errors, examples for RBAC, Kubernetes admission, API authorisation from JWT claims and Terraform plan checks, and a decision log of every input and result.

React render lab Real React 19 running your component on the page, with a live component tree that flashes on every render and says why — which state, which props, which context, or just the parent — render counts and times, a commit timeline, the console, and eleven lessons from lifting state to Suspense, use() and the React Compiler.

Regex railroad diagrams Draw any JavaScript regular expression as a railroad diagram, explain it as a tree, link diagram and source by hover, and export SVG or PNG.

SQL formatter Format SQL for 18 dialects — PostgreSQL, MySQL, SQLite, T-SQL, BigQuery, Snowflake, Spark and more — with keyword case, indent style, and minify.

Tailwind CSS playground Write HTML with Tailwind classes and see it live — Tailwind 4's browser build in a sandboxed preview, your own theme and utilities, a dark-mode switch, phone / sm / md / lg / xl preview widths, a class inspector that explains every utility and shows the CSS it generated, six components to start from, and exports with the CDN or compiled CSS.

TypeScript playground The real TypeScript 6 compiler in your browser — errors with line, column and TS code as you type, hover types, the emitted JavaScript and .d.ts, every strictness flag, a tsconfig.json explained option by option, advanced-type examples, and Run in a sandboxed page or a worker.

Version ranges and SemVer Test version ranges in npm, Cargo, Python, and Maven syntax, inspect and bump SemVer versions, sort version lists, and get the next release from Conventional Commits.

WebAssembly explorer Write WebAssembly text and run it in the page, inspect any .wasm file — sections, functions, sizes, imports, exports, data, an annotated hex dump and a full disassembly — and learn how the format works.

Images and retro graphics

11 ASCII art · Image optimiser and converter · Label maker for Niimbot printers · Media toolbox (ffmpeg) …

ASCII art Turn images into ASCII, colour ANSI, or high-resolution Braille text art, and render FIGlet text banners in 30 fonts, ready to paste into terminals, READMEs, and source comments.

Image optimiser and converter Resize, crop, rotate, and re-encode images as JPEG, PNG, WebP, or AVIF with a before-and-after comparison; strip EXIF; extract a palette; and build favicon and app-icon sets.

Label maker for Niimbot printers Design labels from templates — title, text and QR codes with captions, big text, bins and drawers, barcodes, asset tags, cable flags, Wi-Fi, if-found, food dates, filament spools, warnings, addresses — see them dot for dot, number a run or paste rows from a spreadsheet, and print straight to a Niimbot label printer over Bluetooth or USB.

Media toolbox (ffmpeg) ffmpeg compiled to WebAssembly, in your browser — convert, trim, crop, resize, rotate, re-time and watermark video; make GIFs and animated WebP; extract audio; split video into frames or build video from images; join clips; or run any ffmpeg command.

OCR: text from images and PDFs Read text from photos, screenshots, scans and PDFs with Tesseract compiled to WebAssembly — clean up the image (threshold, deskew, upscale), pick a region, see every word's confidence, and export text, hOCR, TSV or JSON.

Pixel and bitmap editor Draw sprites, tiles, and screens with real hardware palettes — Amiga, C64, NES, Game Boy, ZX Spectrum, Atari 2600, PICO-8, and 1-bit OLEDs — then export C arrays, bitplanes, CHR tiles, sprite data, PNG, or animated GIF.

QR and barcode tool Make QR codes for links, Wi-Fi, contacts, email, SMS, phone numbers, and locations — with colours, logos, PNG and SVG — and read QR codes and barcodes from images or your camera.

Receipt printer Print to-do lists, shopping lists, notes, job cards, daily agendas, recipes, Wi-Fi guest cards, pictures and free-form receipts on a cheap thermal printer — ESC/POS 58 and 80 mm printers over USB, serial or Bluetooth, and the little Bluetooth "cat printers" — with a dot-for-dot preview of the paper strip.

Shader playground Write GLSL fragment shaders and watch them run as you type — WebGL2 with a WebGL1 fallback, compile errors on their lines, Shadertoy's iTime/iResolution/iMouse/iFrame, sliders and colour pickers for your own uniforms, pause, step and scrub, PNG and WebM export, .frag export for Shadertoy, glslViewer and other hosts, share links, and nine examples with lessons from UV gradients to raymarching and a Boing ball.

SVG toolkit Optimise SVGs with SVGO, convert them to PNG, data URIs, CSS backgrounds, and React/JSX components, and combine icons into a <symbol> sprite.

WebGPU compute playground Write WGSL compute shaders and run them on your GPU — compile errors on their lines, buffers set up from the @group/@binding declarations, a pass script for dispatches, loops and uniform writes, results read back into tables and plots, GPU timestamps, and nine examples with lessons from invocation IDs to a parallel scan, tiled matrix multiply, atomics, bitonic sort, particles and a Mandelbrot set.

Video and YouTube

2 Audio loudness meter · YouTube creator tools

Audio loudness meter Measure an audio or video file's loudness in your browser — integrated, short-term and momentary LUFS (ITU-R BS.1770 / EBU R128), loudness range, true peak, sample peak, RMS, DC offset and clipping — compare it with YouTube, Spotify, Apple, podcast and broadcast targets, and export a normalised WAV.

YouTube creator tools Grab a video's thumbnails and check your own at the sizes YouTube shows; build and validate chapters; make share links and privacy-enhanced embeds; count title, description, and tag limits; convert and fix SRT, WebVTT, and SBV captions and clean transcripts; time a script and run a teleprompter; and look up upload bitrates.

AI and machine learning

21 Agent trace viewer · AI cost and energy economics · AI datacenter power and cooling · AI hardware calculator …

Agent trace viewer Open agent traces — Claude Messages API and OpenAI Chat Completions or Responses logs, OpenTelemetry GenAI spans, Claude Code session JSONL — and see every turn, model call and tool call on a timeline and in a tree, with latency, tokens split into cache reads and writes, cost per step, failed tool calls and retries, and full-text search; nothing leaves the browser.

AI cost and energy economics What a token, a training run and a gigawatt datacenter cost: cost per million tokens, 6·N·D training cost, datacenter TCO against GPU life and power price, generation mix and overbuild, PPA prices and energy bills, embodied vs operational carbon, GPU depreciation, and an educational export-control and EU AI Act check.

AI datacenter power and cooling What an AI datacenter's power and cooling add up to: PUE, WUE, CUE and ERE over a year; I²R busbar loss at 12, 48 and 800 V; rack → Scalable Unit → hall in MW; the cooling ladder and die heat flux; coolant flow from Q = ṁ·cp·ΔT with pump pressure ∝ Q²; central-UPS vs 48 V power trains; N+1 and 2N backup; and what a better PUE saves.

AI hardware calculator How much GPU memory an LLM needs and how many accelerators that takes; the roofline model with a batch slider and overlaid chips; training compute, MFU, isoFLOP loss valleys and the EU AI Act line; inference speed, batching, KV hand-off, energy and cost per token; and a sourced table of accelerators from H100 to Groq, Cerebras, Apple silicon and Jetson.

Attention and the KV cache, visually How an LLM's KV cache works and what it costs — one decode step ("read five, compute one") and O(N²) vs O(N) work, MHA/GQA/MQA/MLA head sharing with the live cache size in decimal and binary units, a PagedAttention allocator simulation, FlashAttention's tiles and online softmax with HBM traffic, and long-context cache size, compression and attention FLOPs.

Classic machine learning, step by step Classic machine learning on 2-D data you can edit — a decision tree growing split by split with its best-split search, a random forest's bootstrap trees and vote map, gradient boosting round by round, k-NN, logistic regression, a soft-margin linear SVM and Gaussian naive Bayes side by side — and an optimiser lab racing SGD, momentum, Nesterov, AdaGrad, RMSProp, Adam and AdamW over Rosenbrock, Beale, a saddle and an ill-conditioned bowl with learning-rate schedules.

Collectives and cluster topology Ring and tree all-reduce one step at a time, the α–β time model with the ring/tree crossover and SHARP, the scale-up vs scale-out bandwidth cliff, how an NVL72 rack's 72 GPUs and 18 NVSwitch chips are wired, fat-tree and rail-optimised switch counts, and on-chip ring, mesh and torus hop counts and bisection.

Compute in orbit Size an orbital AI datacenter from first principles: the radiator area to reject the chips' heat by radiation alone (εσA(T⁴ − T_env⁴)), the solar array at 1,361 W/m², the eclipse fraction of the orbit and the battery it needs, and the mass and launch cost.

Embedding explorer Load embeddings (CSV, TSV, JSON, GloVe text, the TensorFlow Projector's vectors.tsv + metadata.tsv) or embed sentences in the browser with all-MiniLM-L6-v2, then project them with PCA, t-SNE or UMAP in 2-D or 3-D, colour and search them, list nearest neighbours by cosine or Euclidean distance, cluster with k-means or DBSCAN, score how faithful the map is, and try word analogies.

Failures, checkpoints and goodput Why a cluster of reliable GPUs fails every few hours (system MTBF = per-GPU MTBF ÷ N, with Llama 3's 419 interruptions in 54 days), the Young/Daly checkpoint interval and the goodput it buys, checkpoint size at 12/14/16 bytes per parameter with synchronous and asynchronous stalls, and inference availability — hot, warm and cold standby and the blast radius of a replica layout.

Links, optics and energy per bit Bandwidth and energy per bit for PCIe 4–7, NVLink 4–6, NVLink-C2C, CXL, UALink, InfiniBand and Ethernet, one way or both; watts per port to pJ/bit and fleet megawatts for copper, pluggable, linear-drive and co-packaged optics; PAM4 symbol rate and Nyquist frequency; transfer times; and the HBM → DDR → CXL → NVMe memory ladder.

LLM eval harness Grade LLM outputs against a dataset — exact match, regex, contains, JSON Schema, numeric tolerance, BLEU (sacreBLEU), ROUGE-L, embedding similarity or an LLM judge — with bootstrap confidence intervals, per-tag breakdowns and run comparisons by paired bootstrap and McNemar's test; paste outputs or call Claude, OpenAI or a local model with your own key.

LLM serving planner The arithmetic of serving an LLM: time per token and throughput against batch size (where the KV cache fills HBM and compute starts to bind), static vs continuous batching animated, pod requests per second and cost per million tokens, a per-request latency waterfall, the prefill-to-decode KV hand-off, speculative decoding, reasoning cost, and prefix-cache economics.

Mixture-of-experts router How a mixture-of-experts router really works: per-token, per-layer top-k with renormalised gates, expert capacity and dropped tokens, auxiliary-loss vs DeepSeek bias vs Expert Choice balancing, active vs total parameters of real models, experts touched per batch, and the all-to-all traffic of expert parallelism.

Model evaluation workbench Evaluate a classifier or regressor from its predictions — paste or upload a CSV, or generate a seeded synthetic model — with confusion matrices (micro, macro and weighted precision, recall and F1, MCC, κ), ROC and precision–recall curves (trapezoid AUC against average precision), lift and gain, a cost-matrix threshold chooser, calibration (reliability diagram, ECE, Brier, Platt and isotonic), class imbalance, per-group fairness, and regression residuals.

RAG chunking playground Drop in text, Markdown, HTML or PDF and chunk it five ways — fixed token windows with overlap, sentences, LangChain's recursive splitter, Markdown headings and semantic breakpoints — see every boundary and overlap on the text, then compare BM25, embedding and hybrid retrieval across the chunkers with recall@k and MRR against passages you mark.

Reinforcement learning gridworld A gridworld you paint — walls, pits, goals, wind and slippery ice — solved by value iteration and policy iteration, and learned by Q-learning, SARSA and Expected SARSA with ε-greedy exploration; value heatmap, policy arrows, Q-values per cell, the reward curve, the cliff-walking race between Q-learning and SARSA, and every Bellman backup written out with the live numbers.

Tokenizer explorer Real tokenizers side by side in your browser — GPT-4/GPT-4o byte-level BPE (cl100k_base, o200k_base), BERT WordPiece, T5 SentencePiece Unigram and Llama 2 SentencePiece BPE with byte fallback — with coloured token boundaries and ids, UTF-8 bytes and split characters, BPE merges step by step, Unicode normalisation, cost per 1k tokens, the common pitfalls, and a tiny BPE you train yourself.

Train a tiny transformer Train a character-level, decoder-only transformer from scratch in your browser — one to four layers, written in plain JavaScript with a hand-written backward pass checked against finite differences — on Shakespeare's sonnets, nursery rhymes, Carroll and Lear, or your own text, and watch the loss fall, the samples turn into words, the attention heads specialise and the character embeddings sort themselves out.

Training memory and parallelism planner How much memory each GPU needs to train a model under data, tensor, pipeline, expert and context parallelism with ZeRO 0–3 / FSDP and activation recomputation, what each axis sends over the network, the pipeline bubble with a 1F1B timeline, MFU vs HFU, an animated activation-checkpointing walk-through, and the memory and FLOPs of PPO, GRPO and DPO.

Yield, chiplets and weights-in-silicon Why big chips are expensive and why AI accelerators are built from chiplets: Murphy, Poisson and negative-binomial die yield, dies per wafer and cost per good die, splitting a design into chiplets with known-good-die testing against the 858 mm² reticle, and the silicon a model needs when its weights are etched into mask ROM.

Electronics

43 Active filter designer · ADC accuracy · Audio oscilloscope · Battery life and power budgets …

Active filter designer Design Butterworth, Bessel, Chebyshev, and Linkwitz–Riley op-amp filters — low-pass, high-pass, band-pass, and notch — as Sallen–Key or multiple-feedback stages with standard resistor and capacitor values, then check the Bode plot, group delay, step response, tolerance spread, and a SPICE netlist.

ADC accuracy Work out effective bits from SINAD or measured noise, build a worst-case and RSS error budget from the reference, gain, offset, INL, and divider tolerances, check whether a divider settles the ADC's sample capacitor in time, and plan oversampling.

Audio oscilloscope A live oscilloscope for your computer's audio inputs — triggered scope with cursors and measurements, XY (Lissajous), spectrum and spectrogram, and a tuner — plus a monitor to listen to the input and a two-channel signal generator for loop-back tests. Audio never leaves the page.

Battery life and power budgets Duty-cycle battery life for IoT devices (sleep, radio bursts, sensor reads, hourly and daily events) with regulator quiescent current, temperature derating, and a daily energy budget; battery chemistries, series/parallel pack builder, charge time, and solar panel and battery sizing.

Battery pack builder Design a lithium battery pack — 18650, 21700, 26650, LiFePO₄ prismatic, or pouch cells in series and parallel (4S2P…) — with its voltage range, capacity, energy, continuous current, weight and size, the BMS and fuse it needs, and the resistance and heating of the nickel-strip links.

Brushless motors — inside and how they are driven How a brushless motor works and how an ESC drives it: Kv, Kt and flux linkage in every convention, torque–speed and efficiency maps, heating, measuring a motor yourself, slot/pole windings drawn with their pattern and winding factor, six-step with Hall sensors and sensorless zero crossings, Clarke/Park, FOC current loops, SVPWM, field weakening, inverter losses, DShot frames and eRPM telemetry — animated and simulated.

Capacitors and impedance Capacitor energy and charge, rectifier ripple and hold-up sizing, supercapacitor backup time, MLCC DC-bias derating, ESR heating and electrolytic life, series stacks with balancing resistors, a comparison of capacitor types — and |Z| and phase of real capacitors, inductors, and resistors, LC tanks, and decoupling networks.

Circuit calculators Ohm's law and power, series and parallel networks of R, C, and L, voltage dividers with standard-value design, LED resistors, Wheatstone bridges, current dividers, and ADC scaling.

Circuit simulator Draw a schematic on a grid and simulate it in the browser — DC operating point with node voltages on the drawing, a transient "oscilloscope" with pulse and sine sources, and AC sweeps with Bode plots — then cross-check it against real ngspice (WebAssembly) or run any SPICE netlist.

Coils and inductors Design and analyse air-core coils (Nagaoka with Rosa's round-wire correction, and Wheeler), multilayer coils, and toroids from their AL value — with turns for a target inductance, wire resistance, skin effect, Q, self-resonance, peak flux, and stored energy.

Connector pinouts Pin-outs for over 100 connectors, each with its source — modern ones (USB-C with CC resistor values, RJ45 and PoE, RS-232, SWD/JTAG, VGA, HDMI, TRRS, Qwiic, OBD-II) and retro computer ports: Amiga Zorro and CPU slots, floppy, video, serial and keyboard; Atari 8-bit SIO, PBI and cartridge; Atari ST ACSI, MIDI and cartridge; C64 expansion, user and IEC ports; the Apple II slot, ZX Spectrum, MSX, BBC Micro, NES/SNES/Mega Drive pads, SCART, ISA, IDE and floppy.

Crystal oscillator Size the load capacitors for a microcontroller's crystal from its load capacitance and the board's stray capacitance, estimate the frequency error of the capacitors you fit, and check the oscillator's gain margin and the crystal's drive level.

Current sensing Choose a current-sense shunt (drop, power rating, error), the gain of a current-sense amplifier into an ADC (INA180 A1–A4), the INA219's calibration register and LSBs, and scale a Hall-effect sensor such as the ACS712.

Decibels and gain chains Convert levels between dBm, dBW, dBV, dBu, dBmV, dBµV, watts, and volts (rms, peak, peak-to-peak) at any impedance; turn decibels into power and voltage ratios; and cascade gain, noise figure, and IP3 through a receiver chain to get its sensitivity and dynamic range.

Digital filter designer Design FIR (windowed sinc, Parks–McClellan, frequency sampling) and IIR (Butterworth, Chebyshev I/II, elliptic) low-, high-, band-pass and band-stop filters for a sample rate, with the order estimated from your ripple and attenuation; see magnitude, phase, group delay, poles and zeros, impulse and step; round the coefficients to Q15/Q31 to see what breaks; export C, CMSIS-DSP and scipy code; and listen to it running on noise, a sweep, your microphone or a file.

Digital logic simulator Build digital circuits by dragging gates, switches, clocks, LEDs and 7-segment displays, watch the signals light up, and go further with flip-flops, counters, adders, an ALU, RAM and ROM, your own sub-circuits, truth tables with minimised expressions, expression-to-circuit, a timing diagram with real gate delays, and a tiny CPU that runs a program.

Discharge curves Simulate how cells and packs discharge under constant-current, constant-power, resistive, and pulsed loads (Li-ion, LiFePO₄, NiMH, alkaline, coin cells, lead-acid), size supercapacitor hold-up, time bleeder resistors, and analyse measured discharge logs.

Electronics handbook A searchable electronics quick reference — Ohm's law to op-amps, filters, biasing and the diode equation, each with a calculator; E series, wire gauge with NEC ampacity, IPC-2221 trace current and clearances, logic levels, IC pinout drawings, decoupling, batteries, connectors and schematic symbols — plus a MOSFET/BJT switch calculator.

Electronics parts inventory and BOM manager A private electronics parts inventory in your browser — scan Digi-Key, Mouser and LCSC bag labels with the camera, identify chips, boards, modules and code-less parts from a photo — by their markings or how they look (on your device), import orders, carts and KiCad BOMs, search by value ("10k 0603 1%"), plan builds for N boards, and get per-supplier purchase lists with price breaks; with storage locations, QR labels printed on sheets or straight to a Niimbot label printer, photos, and optional Digi-Key/Mouser/Nexar API lookups.

Gerber viewer and DFM check Open a zip of Gerbers and drill files, see the copper, mask, silkscreen, paste and outline stacked or as a realistic top or bottom board, measure, and check the design against JLCPCB, PCBWay or OSH Park's published limits — trace width, spacing, drills, annular rings, edge clearance, mask slivers, silk on pads — with every problem marked on the board.

H-bridge and DC motor driver Work out a brushed DC motor's stall and running current, the PWM current ripple for sign-magnitude and locked-antiphase drive, the PWM frequency you need, the H-bridge's conduction, switching and dead-time losses, and what coasting, braking and plugging do.

Interactive assembly BOM Hand-assemble a KiCad board from its .kicad_pcb: the BOM grouped by value and footprint with placed and sourced ticks, the parts of the row you are on lit up on front and back drawings (click a part to find its row), side and DNP filters, progress kept per board, keyboard-driven, stock and bins from your Parts inventory, and a standalone HTML copy to keep with the board.

KiCad board viewer Open a KiCad board (.kicad_pcb, KiCad 6–9) in the browser and look round it — every layer toggled, tracks, vias, zones, pads and footprints drawn as KiCad places them, the back seen from underneath, a net lit up with a click (its pads and track length), measure, find a part, board facts with the smallest clearance, export the visible layers as SVG or PNG, and send the outline to the enclosure maker.

KiCad BOM rollup Turn a KiCad schematic (.kicad_sch with its sub-sheets), XML netlist or BOM CSV into a rollup for N boards: grouped by value and footprint or MPN, plus attrition and spares, checked against your Parts inventory stock, priced at Digi-Key with price breaks, and exported as a Digi-Key order CSV.

KiCad footprint and symbol checker Open KiCad footprints (.kicad_mod, a whole .pretty folder) and symbol libraries (.kicad_sym), see each footprint's pads, courtyard, fab and silkscreen drawn, and get a list of problems with a severity and a one-line reason — courtyard, pin 1, silk on pads, holes and annular rings, paste, origin, naming; and for symbols off-grid and overlapping pins, duplicate numbers, power pin types, hidden power pins, reference, footprint and datasheet fields.

LED drivers Arrange LEDs in series strings with ballast resistors and compare every arrangement, weigh resistors against LM317, two-transistor, and switching constant-current drivers, and plan PWM dimming with gamma-corrected brightness tables for your code.

LED strip and pixel planner Lay out LED strips, frames, rings and matrix panels in millimetres, watch patterns run on them, and get the current, supply, voltage drop and power injection points, feeder wire and fuses, data outputs and frame rate — then export a WLED ledmap and segments, ESPHome YAML, a FastLED XY map and a bill of materials.

Logic levels and level shifting Check whether one chip's output can drive another's input — noise margins and over-voltage across TTL, HC/HCT, LVC, LVCMOS, ESP32, RP2040, STM32, and AVR — pick a level shifter by speed and bus type, design a divider and see its speed limit, and size open-drain pull-ups by rise time.

PCB stackup and impedance Build a PCB layer stackup (or start from typical 2-, 4-, and 6-layer boards), size microstrip, stripline, differential pair, and coplanar traces for 50, 85, 90, and 100 Ω, check them with a built-in 2-D field solver, and budget delay and skew.

PCB traces, vias, and wiring IPC-2221 trace width and current, trace and via resistance, AWG and metric wire tables, cable voltage drop, fuse sizing, and an approximate microstrip impedance.

Pick-and-place file fixer Turn KiCad's position file (or the .kicad_pcb itself) and BOM into the placement file JLCPCB, PCBWay or Seeed want — the right columns, mm or inches, top/bottom naming, origin, bottom-side mirroring, an editable table of per-footprint rotation offsets, DNP left out — with a drawing of every part and its pin 1, and a JLCPCB BOM with LCSC numbers from a field or your Parts inventory.

PID loop simulator Simulate a PID controller on a first- or second-order plant with dead time — step response, overshoot, settling time, a load disturbance, output limits and anti-windup — get gains from Ziegler–Nichols, Cohen–Coon or SIMC tuning rules, copy the controller as C code, and play with a toy glucose loop to see what sensor and actuator delays do.

Power supply design Size the inductor, capacitors, and currents for buck, boost, and inverting buck-boost converters, check linear regulator heat, and budget power, injection, and wiring for WS2812/NeoPixel LED strips.

Reflow profile designer Design a reflow profile from editable zones and check it against the solder paste's window (SAC305 from Indium8.9HF's data sheet, Sn63Pb37 from Kester EP256's) and the J-STD-020E limits for your most sensitive package — ramp, soak, time above liquidus, peak and cooling — on a plot; overlay and compare oven thermocouple logs, and export JSON or CSV.

Resistor colour codes and component markings Read and make resistor colour bands (3 to 6 bands), find the nearest E-series value or the best two-resistor combination, and decode SMD, capacitor, and inductor markings.

RF and wireless calculator Convert dBm, watts, and microvolts; cut antennas for any band; work out free-space path loss, link margin, and Fresnel clearance; calculate LoRa time-on-air and duty cycle; and look up Wi-Fi, BLE, and Zigbee channels.

SMD marking codes Identify a tiny part from the code printed on it — a cited list of common SOT-23, SOD and SMA transistor, MOSFET and diode markings with pinout drawings, EIA-96 and 3- / 4-digit resistor codes, and ceramic, EIA two-character and tantalum capacitor codes.

SMD packages and footprints Chip resistor and capacitor sizes from 01005 to 2512 with power and voltage ratings, the smallest size for a given dissipation, imperial versus metric codes, and a searchable table of diode, transistor, power, SOIC/TSSOP/QFP, QFN/DFN, and BGA packages with body sizes, pitch, and how hard they are to hand-solder.

Thermal design Junction temperature through θJC, interface, and heatsink; MOSFET, regulator, resistor, and diode losses with temperature feedback; finned heatsink performance in still or moving air; PCB copper as a heatsink; pulsed heating from Foster networks; airflow for enclosures; and chip heat flux with the coolant flow liquid cooling needs.

Thermistors and RTDs Convert NTC thermistor resistance and temperature with the Beta model or a Steinhart–Hart fit from three points, design the divider into an ADC with its resolution per degree and self-heating, and convert PT100/PT1000 readings with the Callendar–Van Dusen equation.

Timing, filters, and analog design RC, RL, and LC time constants with charge curves; filter cutoffs with Bode plots; reactance and resonance; 555 timers; op-amp gain and resistor choice; Zener regulators; and linear-regulator heat.

Transistor and MOSFET switches Size the base resistor for a BJT switch, work out a MOSFET's conduction and switching losses and junction temperature from its datasheet, check whether 3.3 V or 5 V drive is enough, design a high-side P-channel switch with an NPN driver, and handle inductive loads.

Wire harness designer Design a wire harness — connectors from a library of common families (JST, Dupont, Molex, Deutsch DT, XT30/60/90, M8/M12, RJ45, D-sub, screw terminals), wires with colours, gauges, lengths, pairs and shields, splices and sleeves — and get the WireViz-style diagram, pin-outs with face views, a BOM with housings and crimp terminals, a cut list, a voltage-drop check, and cable flags for the label maker. Imports and exports WireViz YAML.

Radio and RF

15 Amateur satellite passes · Antenna designer · Digital modes · Feedline and SWR …

Amateur satellite passes Predict passes of the ISS and amateur satellites over your location, with AOS, maximum elevation and LOS times, a sky plot, and Doppler-corrected uplink and downlink frequencies.

Antenna designer Starting dimensions for half-wave dipoles and inverted-Vs, quarter-wave verticals and ground planes, J-poles, Moxon rectangles (W4RNL's equations), a 3-element Yagi and the end-fed half wave — with harmonic checks against the amateur bands and turns for 1:1 to 64:1 baluns and ununs.

Digital modes Decode FT8, PSK31, RTTY, CW and SSTV from a microphone, line-in, an audio file or the SDR receiver — FT8 with UTC slot timing, SNR, DT and frequency; make PSK31, RTTY and SSTV audio; and map WSPR and PSK Reporter spots for a callsign.

Feedline and SWR Convert between SWR, reflection coefficient, return loss, mismatch loss and reflected power; work out coax loss for RG-58, RG-8X, RG-213, LMR-240/400/600, Ecoflex 10, Aircell 7 and RG-6 at any length and frequency, including the extra loss from SWR and the SWR the transmitter sees; and electrical lengths for stubs and phasing lines.

Ham radio toolkit Look up any frequency in the ITU, US, UK, and IARU Region 1 band plans; find a callsign's country, zones, and beam heading; convert Maidenhead locators and work out distance and bearing; and check repeater offsets, CTCSS and DCS tones, Q-codes, and phonetics.

Impedance matching networks Design L-networks (both topologies, both solutions), Pi and T networks for a chosen Q, single shunt-stub matches and quarter-wave transformers for any load, with component values at the frequency, the loaded Q and bandwidth, and a check of the resulting input impedance.

LoRa airtime and duty cycle Time on air for any LoRa packet, LoRaWAN data rate or Meshtastic preset, and what it means: messages per hour under the EU duty-cycle sub-bands, the US 400 ms dwell time and TTN's fair-use policy, sensitivity and range per spreading factor, an airtime chart and a battery estimate.

LoRaWAN frame decoder Decode a LoRaWAN PHYPayload — join requests and accepts, uplinks and downlinks with every FHDR field — check the MIC, decrypt the payload with your session keys, decrypt join accepts and derive the session keys, read MAC commands, and decode CayenneLPP.

Meshtastic packet decoder Decode Meshtastic packets from hex, base64 or a live MQTT feed — ServiceEnvelopes, MeshPackets, Data and raw over-the-air frames — decrypting channel traffic with your keys, with a byte-by-byte field view and a list and map of the nodes heard.

Meshtastic toolkit Connect to a Meshtastic node over Bluetooth or USB to see its nodes, telemetry, channels and config and send messages; decode and make channel URLs and QR codes; plan LoRa links for every modem preset with a terrain profile; simulate flooding through a mesh; and map nodes from MQTT.

Morse code trainer and decoder Learn Morse with the Koch method and Farnsworth spacing, send text as sound or a flashing light, and decode CW from the microphone or an audio file in the browser.

Propagation and logbook The greyline on a world map now or at any time, solar flux and Kp from NOAA, a simple MUF and band-opening estimate for a path, beam heading and distance, an ADIF logbook with dupe checks, statistics, a contact map and POTA/SOTA activations, and APRS — decoded from packets, KISS or a live APRS-IS feed — on a map.

RF filters and attenuators Design Butterworth and Chebyshev LC ladder filters (low-pass, high-pass and band-pass) with the order for your stop-band spec and the response computed from the component values, and resistive attenuator pads — Pi, T, bridged-T and minimum-loss — with the power in each resistor and the nearest standard values.

SDR receiver A software-defined radio in the browser — an RTL-SDR dongle over WebUSB, an rtl_tcp server, a recorded IQ file or a built-in test band — with a spectrum and waterfall, click-to-tune, WBFM, NBFM, AM, USB, LSB and CW, squelch, band presets, bookmarks, and audio and IQ recording.

Smith chart An interactive Smith chart: plot a load (or click to place one), add series and shunt inductors, capacitors and resistors, lengths of line and stubs, and watch the impedance move towards the centre — with the admittance grid, the VSWR circle, a table of every point and CSV/JSON export.

FPGA and HDL

3 FPGA calculators · FPGA playground · HDL trainer: learn Verilog by doing

FPGA calculators Setup/hold slack with a timing diagram, clock-domain crossing patterns with Verilog and synchroniser MTBF, iCE40 and ECP5 PLL settings that match icepll and ecppll, FIFO depth, VESA/CTA-861 video timings with a Verilog generator, UART divisors, BRAM/DSP counts, parallel CRC and LFSR generators, and pin-constraint files for eleven boards.

FPGA playground Write Verilog, simulate it with Icarus Verilog, synthesise with Yosys and build a bitstream for Lattice iCE40, ECP5, CrossLink-NX, MachXO or Gowin FPGAs — or synthesise for Xilinx and Intel and export a Vivado or Quartus project — with the real open-source FPGA tools in your browser, and 44 documented examples.

HDL trainer: learn Verilog by doing Learn Verilog by writing it: 23 lessons from gates to UARTs, VGA timing, FIFOs and pipelines, each checked by a hidden testbench that simulates your module and shows the waveform and every mismatch — plus a sandbox simulator and a logic-sim → Verilog converter.

IoT and embedded

25 ARM Thumb assembly playground · Battery-life estimator · Bluetooth LE explorer · Board pinouts …

ARM Thumb assembly playground Write Cortex-M assembly and step through it on a simulated microcontroller: a GNU-syntax assembler for Thumb and Thumb-2 with literal pools and IT blocks, every 16- and 32-bit encoding split into its fields bit by bit, registers and NZCV with changes highlighted, memory and stack views, breakpoints, LEDs and switches on GPIO, a UART terminal, SysTick interrupts through a vector table, and Cortex-M0 or M3 cycle counts.

Battery-life estimator How long a microcontroller project runs on its battery — a duty cycle built from datasheet currents for the ESP32, ESP32-C3, ESP32-S3, nRF52840 and RP2040 (each cited to its table), capacity derating for temperature, ageing and cut-off, self-discharge, and an LDO's quiescent current or a switcher's efficiency — with a one-cycle current timeline, where the charge goes, and what-ifs.

Bluetooth LE explorer Connect to a Bluetooth Low Energy device from the browser, browse its GATT services, read, write, and subscribe to characteristics with decoders for standard sensors, graph live values, and look up UUIDs.

Board pinouts Interactive pinouts for 36 boards — ESP32, -S2, -S3, -C3, -C5, -C6, -H2 and -P4 (Espressif DevKits, XIAO, Adafruit QT Py and Feather V2, ESP32-CAM, Nano ESP32), ESP8266, Raspberry Pi Pico and Pico 2, Arduino Uno R3/R4, Nano, Mega and Leonardo, Pro Micro, Teensy 4.0, STM32 Blue and Black Pill, and the Raspberry Pi header — with a pin planner, board comparison, and ESPHome/Arduino/MicroPython export.

Boing Lamp effect lab Write effects for the Boing Ball lamp in JavaScript, the way the firmware's are written — render(ctx, out) over the lamp's 128 cells — watch them on a 3-D ball with the lamp's real cells and on a flat map, stream them to the lamp over Bluetooth, or run them as a full-screen screensaver that shuffles the effects and bounces the ball.

Boing Lamp over Bluetooth Control the Boing Ball lamp from the browser over Bluetooth — the lamp's own control page (effects, brightness, playlist, clock and weather, LED calibration, WiFi set-up) with every request carried over BLE, plus a console for its text commands.

Bus protocols, simulated Type a transaction (bytes, addresses, read or write) for SPI, I²C, UART, 1-Wire, SD card SPI-mode init or JTAG and get a zoomable, animated timing diagram with every phase labelled. Step through it bit by bit with an explanation of each one, inject errors to see how a decoder reacts, or paste a capture and decode it.

CRC and checksum calculator Compute any of 40 standard CRCs (CRC-8 to CRC-64) or define your own, identify an unknown CRC from an expected value, generate C code, and calculate checksums, NMEA, Luhn, and Modbus RTU frames.

ESP firmware image inspector Open an ESP32-family .bin — app image, bootloader, partition table, NVS partition, or a full-flash dump — and see its header, segments, app description, checksum and SHA-256 verification, partitions, OTA state, and every NVS key and value.

ESP flasher Flash, erase, verify, and back up ESP8266 and ESP32-family chips from the browser over Web Serial — offsets from file names or an ESP-IDF build folder's flasher_args.json, merged images, security state, region erase and read-back.

ESP32 crash decoder Paste a Guru Meditation, abort, assert, watchdog, or brownout log from an ESP32, S2, S3, C3, C6, or H2 and get the cause explained, the registers annotated, the backtrace resolved against your ELF, and the reset reason decoded.

ESP32 partition table editor Design ESP-IDF and Arduino-ESP32 partition tables visually — add OTA, NVS, SPIFFS, LittleFS, and FAT partitions, check alignment and overlaps, and export the CSV or a flashable partitions.bin.

ESPHome config builder Build ESPHome device YAML from a board and a catalogue of sensors, switches, lights, and buses — with live output, a secrets.yaml template, and a linter for pin conflicts, strapping and flash pins, ADC2 with Wi-Fi, I²C address clashes, and ESP8266/ESP32 differences.

I²C address finder Pick the devices on an I²C bus and see the 7-bit address map with clashes and reserved addresses, the address-pin strapping that makes them fit, and a TCA9548A multiplexer plan when they can't share one bus — for 53 common sensors, displays, expanders, ADCs, RTCs and EEPROMs.

Logic analyser Open VCD, Saleae, or sigrok captures (or raw bytes) in the browser, zoom and measure the waveforms with cursors, and decode UART, I2C, SPI, and 1-Wire traffic into bytes, text, and a searchable event list.

Microcontroller timing calculator Baud-rate register values with error for AVR, STM32, and ESP32 UARTs; timer prescaler and period solver; ESP32 LEDC PWM resolution; I²C pull-up sizing with an address directory; and SPI clock dividers.

Modbus and CAN bus workbench Build and decode Modbus RTU, ASCII, and TCP frames, decode registers in every word order, draw CAN bit streams with stuff bits and CRC-15, calculate MCP2515, ESP32 TWAI, STM32, and SJA1000 bit timing, estimate bus load, and decode DBC signals, candump logs, OBD-II PIDs, and J1939 IDs.

MQTT client Connect to an MQTT broker over WebSockets, subscribe with wildcards, watch messages as a live log and topic tree, and publish text, JSON, or binary — for testing IoT devices and Home Assistant setups.

Peripheral protocols, simulated Compose PS/2 keyboard and mouse traffic, WS2812 pixel data, IR remote codes (NEC, RC5, RC6, Sony), DMX512 packets, MIDI bytes and Centronics printer handshakes, and step through the timing diagram bit by bit — with error injection, decoders for pasted captures and Flipper/IRremote files, VCD export and a hand-off to the logic analyser.

PIC microcontrollers Pinouts and specifications for 16 popular Microchip PICs from the PIC10F200 to the PIC18F45K22, a configuration-bits generator and decoder (XC8, pic-as, MPASM), timer, PWM, baud-rate, I²C and A/D clock calculators, a PIC16F84A assembler and simulator with LEDs, buttons and a 7-segment display, and an Intel HEX inspector.

Pico hardware bench Turn a Raspberry Pi Pico (or an ESP32) running stock MicroPython into a bench tool driven from the browser — GPIO and PWM, an I²C scanner with register reads, SPI with flash JEDEC ID decoding, a UART bridge, 1-Wire thermometers, a live ADC plot, a PS/2 keyboard sniffer, and a PIO logic capture that opens in the logic analyser. No custom firmware.

PlatformIO project helper Build, explain, and lint platformio.ini files — resolve extends, [env] inheritance, and ${…} interpolation per environment, pick boards with real IDs, and get the pio and Arduino CLI commands for each environment.

RISC-V assembly playground Write RV32IM assembly and step through it: an assembler with pseudo-instructions and %hi/%lo, the machine code beside each line with every format's fields decoded bit by bit, registers with changes highlighted, memory and stack views, breakpoints, RARS-style ecalls, LEDs and switches on a memory-mapped device, and a 5-stage pipeline diagram of what ran, with stalls, forwarding and flushes.

Sensor register decoder Turn raw I2C register bytes from BME280/BMP280, MPU-6050, INA219, ADS1115, SHT3x, DS3231, and DS18B20 into calibrated readings using the datasheet formulas, and build the configuration registers and I2C transactions to set them up.

Serial monitor and ESP flasher A Web Serial terminal and live plotter for Arduino, ESP32, ESP8266, and Pico boards, plus an ESP firmware flasher built on esptool-js — all in the browser, no drivers or IDE.

Medical engineering

16 Batch, tolerance and shelf life · Biosignal analysis · CT and MRI lab · DICOM viewer and de-identification check …

Batch, tolerance and shelf life Break-even between making processes on a log quantity axis, worst-case and root-sum-square tolerance stack-up, Cp and Cpk from pasted measurements with a histogram, surface roughness by process against a bacterium and the 0.8 µm hygienic line, and ASTM F1980 accelerated-ageing times.

Biosignal analysis Load an ECG, PPG or EMG recording (CSV, PhysioNet WFDB, EDF) or a synthetic sample, filter out wander and mains, detect ECG beats with Pan–Tompkins and correct them, compute RR intervals and HRV, see why a PPG ratio-of-ratios is not an SpO₂ reading, and find EMG onsets — analysis of recordings for learning, not a medical device.

CT and MRI lab CT reconstruction from scratch (projections, sinograms, Poisson noise, back-projection, FBP and SART), Hounsfield units with window/level, k-space masking, MRI spin-echo contrast, and how a segmentation threshold moves a measured dimension.

DICOM viewer and de-identification check Open DICOM files or a folder of slices in the browser — every tag including private ones, flagged against the PS3.15 Annex E de-identification profile; Hounsfield units, window presets, distances in mm and region statistics; what the slice thickness can support; and an anonymised copy with a list of what changed.

Diffusion, dialysis and clearance Diffusion time t ≈ x²/2D and surface-to-volume 3/r; fit a diffusion coefficient from your own dye-in-agar measurements; dialyser clearance and Kt/V; a week of kidney filtration against haemodialysis; and an animated co-current against counter-current exchanger. Educational simulation only.

Half-lives, decay and steady state A one-compartment model of an invented drug — single or repeated doses, accumulation, steady state after 4–5 half-lives, bioavailability and a loading dose against an invented window band — plus fraction-remaining tables, F-18 and Tc-99m decay with the FDG SUV decay-correction exercise, and hormone half-lives read as time constants.

Health data and medical software Orientation for health software: place an app in the IMDRF SaMD table, work out k-anonymity from cell counts or a CSV, check the 18 HIPAA Safe Harbor identifiers, build and validate a FHIR Observation (LOINC code, UCUM unit, status, time, subject), explore an HL7 v2 message, tamper with a hash-chained audit log, and fill in a STRIDE table.

Heart, vessels and oxygen Cardiac output, ejection fraction, MAP and pulse pressure; ΔP = Q × R for the systemic and pulmonary circuits with a pressure cascade; Poiseuille's r⁴ for a vessel, a stenosis or a strap; Dalton, Henry and cylinder arithmetic; and the oxygen–haemoglobin dissociation curve with temperature, CO₂ and pH shifts. Educational simulation only.

Labels, alarms and the senses Size letters for a viewing distance and a user's acuity (or find how far a label can be read), visual angle in arcminutes, dioptres and reading adds by age, the blind spot, whether an alarm is heard over room noise at a distance, the 3-dB exposure rule, ear-canal resonance and middle-ear gain, two-point discrimination, and a colour-vision and blur check of a photo of your label.

Levers, moment arms and contact Drag an idealised elbow model and watch the perpendicular moment arm, the cord force (with and without the forearm's own weight) and the cord travel change through the sweep, with the lever class and every assumption listed — plus average contact pressure with everything it cannot tell you, and the energy of a fall.

Project worksheets for medical makers The reusable worksheets from Human Biology for the Medical Maker as one fillable, versioned project file — brief with a need-statement checker, evidence separation, task map, constraints sweep, hazard chain ranked by judgement (no scores), requirements with a de-adjective helper, test and version records with change impact, a traceability matrix that shows the gaps, learning objective with a Bloom check, bench-result sentence and handover checklist. Saves in your browser; exports Markdown, CSV and JSON; prints cleanly.

Test accuracy and risk A diagnostic test's 2×2 table from counts or from sensitivity, specificity and prevalence, drawn as 1,000 people; PPV and NPV against prevalence; ROC curves with a threshold slider and AUC; alarms as a low-prevalence test; relative versus absolute risk and NNT; and why reference ranges flag healthy people.

Test lung and breathing mechanics A simulated test lung: pressure, flow and volume waveforms from the equation of motion in volume and pressure control, time constants and breath stacking, a lung-volumes spirogram, dead space, airway radius to the fourth power, and Laplace's law. Educational simulation only.

Tissues, materials and temperature Tissues against engineering materials on one log scale of stiffness and strength, with the stress-shielding ratio; polymer glass-transition and service temperatures against laundry and steam-sterilisation temperatures, with the evidence gaps each figure leaves; and thermal expansion with the borosilicate versus soda-lime glass comparison.

Ultrasound, Doppler and dose numbers Pulse-echo depth, wavelength, depth limit and frame rate; reflection at impedance boundaries; the Doppler shift and how an angle error moves the velocity; ultrasonic ranging in air; effective dose against natural background; Beer–Lambert, inverse square, and √N counting noise.

Unit-safe clinical arithmetic Clinical unit arithmetic that refuses a number without its unit — glucose, creatinine, BUN, HbA1c and any substance by molar mass; % w/v to mmol/L to mOsm/L; pressure; creatinine clearance with a unit-error demonstration; an infusion error drill on invented scenarios; insulin strengths; and body surface area per kilogram.

Chemistry

7 Chemistry: formulas and the periodic table · Isotope patterns and exact mass · Molecule viewer (SMILES) · Solutions and lab maths …

Chemistry: formulas and the periodic table Molar mass and percent composition from any formula (hydrates, ions, nested brackets), mass ↔ moles ↔ particles, empirical formulas, an equation balancer that handles ionic and redox equations, an interactive periodic table, and electrochemistry: galvanic cell EMF from standard electrode potentials and Faraday's law for plating and corrosion.

Isotope patterns and exact mass Monoisotopic, average, and nominal mass for any formula; the isotope distribution as a stick spectrum at unit or fine resolution; m/z for common ESI adducts; and ppm mass error.

Molecule viewer (SMILES) Type a SMILES string, a molecular formula or a name (about 630 molecules built in, plus PubChem search) to draw the 2D structure and get the formula, masses, rings, H-bond donors and acceptors, rotatable bonds, TPSA, cLogP and the Lipinski and Veber rules — plus, with RDKit in WebAssembly, canonical SMILES, InChI/InChIKey, exact descriptors, SMARTS substructure search and fingerprint similarity. Load a protein from the Protein Data Bank by ID (1A3N haemoglobin, 4INS insulin) in 3-D and export it as an STL for printing.

Solutions and lab maths Make up solutions by weight, convert between molarity, % w/v, % w/w, ppm, molality and normality, plan dilutions and serial dilutions, calculate pH, design buffers, solve the ideal gas law and limiting-reagent problems, work out osmolarity and tonicity (van 't Hoff factor, permeant solutes), and do the available-chlorine arithmetic for disinfectant tablets.

Spectroscopy and calibration curves Beer–Lambert solver with absorbance ↔ transmittance, a calibration-curve fitter (linear, through zero, or quadratic) with R², LOD/LOQ and back-calculated unknowns, and light conversions between wavelength, wavenumber, frequency, and photon energy with the visible colour.

Thermochemistry Reaction enthalpy, entropy and Gibbs free energy from standard formation data, with ΔG and K against temperature, Hess's law solved automatically, ΔG° ↔ K and van 't Hoff, calorimetry, and bond-enthalpy estimates.

Titration curves Simulate acid–base titration curves exactly for strong, weak, polyprotic, and mixed acids and bases, find equivalence and half-equivalence points and buffer regions, choose an indicator by titration error, and analyse your own pH-meter data by derivative and Gran plots.

Biology

8 DNA, RNA, and protein sequences · Genetics: Punnett squares and Hardy–Weinberg · Growth curves · Identify plants, birds and insects …

DNA, RNA, and protein sequences Paste a sequence or FASTA: composition and GC%, complements, translation in six frames with any genetic code, ORFs, codon usage, restriction sites and virtual digests, primer Tm (nearest-neighbour), and protein MW, pI, extinction coefficient, and hydropathy.

Genetics: Punnett squares and Hardy–Weinberg Punnett squares for mono-, di-, and trihybrid crosses with phenotype and genotype ratios (complete, incomplete, or codominance), X-linked crosses, Hardy–Weinberg with a χ² test, carrier frequency from incidence, recessive-disease pedigree risk, and recombination frequency ↔ map distance.

Growth curves Fit logistic, Gompertz, and Baranyi growth models to OD time courses from a plate reader, get lag time, μmax, doubling time, and maximum OD for every well with replicate summaries, and plan cell-culture passaging with seeding densities and split ratios.

Identify plants, birds and insects Point your camera (or open a photo) at a plant, bird or insect and get the five most likely species — recognised on your device by Google's AIY Vision classifiers (2,101 plants, 964 birds, 1,021 insects), or rank your own labels with OpenAI's CLIP. Pictures never leave the page.

Lab calculations for biology Haemocytometer counts and seeding, doubling time, centrifuge RPM ↔ ×g, PCR master mixes, A260 quantification and purity, copy number, ligation ratios, oligo resuspension, OD600 → cells, unit conversions, and growth arithmetic: PCR efficiency, exponential growth, tumour doublings, and log reduction, D-values and the sterility assurance level.

Plasmid map Paste a GenBank record or FASTA and get a circular plasmid map with feature arcs and single/double cutters, edit and auto-annotate features, run virtual digests on a simulated gel, and export SVG, PNG, GenBank, or FASTA.

Sequence alignment Global (Needleman–Wunsch), local (Smith–Waterman), and semi-global alignment of DNA or protein with BLOSUM/PAM matrices and affine gaps; colour-coded output, identity and similarity, the DP matrix with its traceback, and a dot plot.

Survival analysis Kaplan–Meier curves with Greenwood confidence bands, median survival, a number-at-risk table, log-rank (and Gehan–Breslow, Tarone–Ware) tests for two or more groups, and Mantel–Haenszel hazard ratios — from a time, event, group CSV.

Physics and units

16 Beams, columns and trusses · Earthquakes, live · Fluid flow and pipe pressure drop · Lasers and fibre optics …

Beams, columns and trusses Beam solver for simply supported, cantilever, propped, fixed and overhanging beams with point, uniform, triangular and moment loads — shear, moment, slope and deflection diagrams, stresses from a section-property calculator, steel, aluminium, wood and 3D-printed materials — plus Euler and Johnson column buckling and a drawable 2-D truss solver with tension, compression and member buckling.

Earthquakes, live Earthquakes from the USGS live feeds (past hour to past 30 days) or any date range from its catalogue, on a world map with plate boundaries — sized by magnitude, coloured by depth or age — with a filterable list, details (PAGER alert, felt reports, tsunami flag, ShakeMap), distance from you and when the P and S waves reach you, a Gutenberg–Richter plot with the b-value, and what each step of magnitude means in energy.

Fluid flow and pipe pressure drop Reynolds number and Darcy–Weisbach pressure drop with Colebrook, Swamee–Jain, or Haaland friction factors and fitting losses; Hagen–Poiseuille laminar flow with an r⁴ sensitivity plot; pipe sizing from flow and velocity; Bernoulli solver; hydrostatic pressure and buoyancy; pump power and orifice flow — with unit-aware inputs.

Lasers and fibre optics Gaussian beams (waist, Rayleigh range, divergence, w(z), R(z), Gouy phase, M²), focusing to a spot and beam expanders, ABCD q-parameter propagation through a train of lenses with an animated full-screen envelope plot, two-mirror cavity stability on the g₁g₂ diagram, fibre NA, V number, modes, cutoff and Marcuse mode field diameter, a dB link budget, modal and chromatic dispersion, approximate laser-safety MPE and NOHD, and photon arithmetic.

Lens design bench A sequential lens design bench: build a prescription of spherical and conic surfaces in N-BK7, N-SF11, F2, N-SK16, fused silica, CaF₂ and plastics (Sellmeier data), trace paraxial and real rays, get the cardinal points, Seidel aberrations and longitudinal colour, spot diagrams, ray fans and an MTF estimate, bend a singlet, design an achromatic doublet, and export the prescription as CSV or JSON — with a full-screen layout.

Linkages and mechanisms Mechanisms you can play with — an animated four-bar linkage with the Grashof check, its type, the coupler curve and the transmission angle; slider-cranks with stroke and quick return; disc cams with uniform, harmonic, cycloidal and 3-4-5 motion, pressure angle and undercut check; a 2- or 3-link robot arm you drag by the hand, with both inverse-kinematics solutions; and differential-drive kinematics and odometry for small robots.

Model rocketry Simulate a model rocket's flight from real motor thrust curves — altitude, speed and acceleration, apogee, the right ejection delay, launch-rod speed and descent under the parachute — check its stability with the Barrowman centre of pressure and a side-view drawing, size the parachute, and look up motor classes and the NAR/Tripoli safety codes.

Orbital mechanics An n-body gravity simulator with presets (Sun–Earth–Moon, inner planets, the figure-eight three-body orbit, a binary star, a Jupiter Trojan), plus Hohmann transfer, Kepler's-law, escape-velocity, and orbital-element calculators.

Physics calculators Physical constants and calculators for kinematics, projectiles with air resistance, oscillations, forces on an incline, collisions, waves and sound, lenses and refraction, the eye in dioptres (far point, accommodation by age, reading add), heat, gases, and orbits.

Polarization Polarised light, interactively: the polarisation ellipse from a Jones vector, an optical train of polarizers, waveplates and rotators you drag and turn (Jones calculus), Malus's law and the three-polarizer paradox, Stokes parameters on a draggable 3-D Poincaré sphere, the Fresnel equations with Brewster's angle and total internal reflection, calcite's double image, waveplate thickness, computed interference colours with a Michel-Lévy chart, photoelastic stress fringes, and how sunglasses, LCD pixels and 3-D glasses work.

Room acoustics and sound Decibel addition and background correction, inverse-square distance loss, room modes with a chart, RT60 by Sabine and Eyring from a materials table, speed of sound and wavelength, note ↔ frequency with adjustable A4, and a tone, noise, and sweep generator.

Skew-T sounding A Skew-T log-P diagram for any place from Open-Meteo's forecast, or for a radiosonde sounding pasted from the University of Wyoming — temperature and dewpoint, dry and moist adiabats, mixing-ratio lines, wind barbs, a surface, mixed-layer or most-unstable parcel with CAPE and CIN shaded, LCL, LFC and EL, lifted index, precipitable water, freezing level, shear, storm motion and helicity, a hodograph, and a plain-English reading.

Spectrum analyser Generate, load, or record a signal and analyse it: waveform, FFT spectrum with window functions and averaging, peak detection, an STFT spectrogram, and THD / THD+N / SINAD for a test tone — plus synthetic ECG, EMG, EEG and PPG with mains hum, baseline wander and noise, and a signal-averaging demo.

Telescopes and optics Telescope and eyepiece arithmetic (magnification, focal ratio, exit pupil, true field, useful power, Dawes and Rayleigh limits, limiting magnitude, Barlows and reducers), a camera on a telescope (arcseconds per pixel and sampling), binoculars, an interactive ray-tracing bench where you drag lenses and mirrors and watch images form, the lensmaker's equation and Snell's law with total internal reflection.

Unit converter Convert between hundreds of units — length to radiation dose — or type a query like “3.5 ft·lbf to N·m” and let dimensional analysis do the rest.

Wave optics lab An interactive wave-optics lab: Young's slits and gratings, thin-film colours of soap bubbles and coatings computed spectrally (transfer-matrix method, CIE 1931 colour), Michelson and Fabry–Pérot interferometers, Newton's rings, the slit and Airy patterns with the Rayleigh criterion, any aperture's diffraction pattern by 2-D FFT (draw your own), Fresnel diffraction with the Cornu spiral, a grating spectrometer, and a ripple tank simulation.

Mathematics

34 Algebra step by step · Boolean logic · Calculus, visually · Complex numbers, visually …

Algebra step by step Solve linear equations, inequalities, quadratics and simultaneous equations with every step explained; divide and factor polynomials; explore a quadratic in four synchronised views with a draggable vertex, watch its roots move through the complex plane, draw sign charts for quadratic and rational inequalities; slide a, b, h and k to transform a graph; and practise with generated problems that check your answers.

Boolean logic Truth tables with a column for every sub-expression, push negations inward one named law at a time, brute-force SAT on CNF clauses, Quine–McCluskey minimisation with Karnaugh maps and gate diagrams, equivalence checks, and register bitfields.

Calculus, visually Drag a secant into a tangent, play the ε–δ game, build f′ from slopes, race Riemann sums, the trapezoid and Simpson's rules on a log–log error plot, paint the area under a curve, and watch Taylor polynomials, linearisation and optimisation work — with every number beside the picture.

Complex numbers, visually Drag z and w to see addition as vectors and multiplication as rotate-and-scale; modulus and argument with the arctan quadrant trap; Euler's formula with its power series as a spiral of arrows; De Moivre and nth roots; z ↦ wz and z ↦ z² acting on shapes and grids; quadratic roots leaving the real axis; AC phasors and three-phase; and the Mandelbrot set with orbits and the limits of double precision.

Conics, pixels and metrics Coordinate geometry you can drag: conics from a focus, a directrix and an eccentricity slider (and from slicing a cone), a parabolic reflector, Bresenham, DDA and anti-aliased lines stepped pixel by pixel with the decision value D, Lᵖ unit circles and A* heuristics, the inscribed angle and Thales, a line meeting a circle via the discriminant, and world-to-screen mapping.

Control systems Enter a plant as a transfer function — polynomials or poles, zeros and gain, continuous or sampled — or pick a DC motor, mass–spring–damper, inverted pendulum, thermal or dead-time preset, add a P, PI, PID or lead/lag controller, and see the step and impulse responses with rise, overshoot, settling and steady-state error, the Bode plot with gain and phase margins, the Nyquist plot, a root locus you drag the gain along, and the closed-loop pole–zero map, with Ziegler–Nichols, IMC and SIMC tuning.

Counting, visually Counting you can see: Pascal's triangle to row 64 coloured mod 2, 3 or 5 with parents and hockey sticks, the binomial theorem as "pick x or y", draggable stars and bars, lattice paths and MISSISSIPPI, an enumerator that shows when a construction counts something twice, derangements and 1/e, next permutation step by step, a backtracking tree with pruning, product-rule stages with password keyspaces, and birthday and hash collisions.

Eigenvectors at work: Markov chains, PCA, SVD Eigenvectors doing real jobs — a Markov chain editor with its steady state and spectral gap (and PageRank), power iteration, Fibonacci by matrix powers against Binet's formula, the Leslie population model, PCA by rotating a line through a cloud, SVD image compression of your own photo with its rank-1 layers, and latent semantic indexing.

Fourier series See how sums of sines build any periodic function: coefficients and partial sums for square, sawtooth, triangle, custom, or hand-drawn waves, the Gibbs phenomenon and Fejér smoothing, amplitude and phase spectra, rotating epicycles, a draw-any-shape complex Fourier demo, the DFT as arrows that line up or cancel, and the N² against N log N cost of the FFT.

Geometry: triangles, circles, polygons, solids Solve any triangle from three values (including both answers of the ambiguous SSA case) with a drawing; arcs, chords, and rise; circle through three points; regular polygons with mitre angles; volumes and surface areas of solids; and coordinate geometry with shoelace area.

Graph algorithms Draw a graph (or open one of the book's) and step through the classic algorithms one move at a time: degrees, components and Euler trails; the adjacency matrix and walk counts; BFS racing DFS through a maze; Dijkstra and Bellman–Ford (with a negative edge and currency arbitrage); Kahn's topological sort and the critical path; Kruskal and Prim; greedy and bipartite colouring; Hamiltonian tours by brute force against nearest neighbour; and PageRank by random surfers and power iteration.

Graphing calculator Plot functions, parametric and polar curves with live parameter sliders; find roots, extrema, and intersections; show derivatives and integrals; and use a scientific calculator.

Kalman filter playground Tune a Kalman filter live and watch it work — a 1-D value, 2-D tracking with constant-velocity and constant-acceleration models, an extended Kalman filter for a range–bearing sensor, GPS + accelerometer fusion, and complementary filter against Kalman for tilt (with your phone's sensors) — stepping through predict and update with every matrix shown, covariance ellipses, innovations and NIS/NEES consistency against chi-square bounds.

Linear systems, visually Enter a system of linear equations and see it — lines in 2-D, planes in 3-D — then solve it yourself with exact row operations (swap, scale, add a multiple) with undo, hints and "show me", while the picture updates. Classifies one / none / infinitely many solutions, and shows Cramer's rule and least squares. Plus linear programming with a sliding objective line, and an ill-conditioning demo.

Maths practice gym Practise the skills from arithmetic to intro calculus — a skill tree of 33 skills, generated problems checked by equivalence, step-by-step checking that names your mistakes, timed drills, an adaptive placement test, and spaced-repetition review, with progress kept in your browser.

Matrix calculator Linear algebra with exact fractions or decimals — products (stepped row × column), determinant, inverse, rank, RREF step by step, Ax = b, null space, LU, QR, eigenvalues and eigenvectors (with the 2×2 procedure by hand), norms, and condition number.

Matrix transformations See what a 2×2 or 3×3 matrix does: the grid, the unit square or cube, the basis vectors and a shape move live as you edit entries or drag the columns — animated from the identity, with the determinant as signed area or volume, eigenvectors, composition, the inverse, presets, the SVD as rotate–stretch–rotate, rotation about a pivot with 3×3 homogeneous matrices, and a neural-network layer folding the plane with ReLU.

Neural network designer Build a multi-layer neural network from a palette, see every tensor shape and parameter count, draw it, train small ones live in the browser, and generate runnable PyTorch, Keras 3, JAX/Flax or plain NumPy code.

Number theory Arbitrary-precision integer tools — primality, factorisation, divisor functions, GCD and modular arithmetic, the Chinese remainder theorem, bases, repeating decimals, continued fractions, big factorials, and Roman numerals.

Number theory step by step The working behind the answers — Euclid as a trace table and as square tiles, extended Euclid with back-substitution, the two-jug puzzle, an animated sieve, trial division, clock arithmetic and its cardioids, mod-m tables, % on negative numbers, square-and-multiply against naive powers, repeating decimals, LCGs, check digits, Diffie–Hellman and RSA.

ODE solver and phase portraits Solve systems of ordinary differential equations with Euler, RK4, or adaptive Dormand–Prince RK45; see time series and phase portraits with direction fields, nullclines, clicked trajectories, classified equilibria, and a rotatable 3-D view. Plus a slope field with Euler's method against the exact solution, and an integrator shoot-out showing energy drift.

Probability: dice, cards, Bayes Exact dice distributions with a chart; exact permutations and combinations; poker and lottery odds; the birthday problem; binomial, hypergeometric, geometric, and Poisson; Bayes with a natural-frequency tree and icon array; Bloom filters; a naive-Bayes spam filter; series/parallel reliability; expected value and Monte Carlo.

Root finding, step by step Bisection, Newton, secant and fixed-point iteration side by side, one step per click, with tangents, secants, a cobweb diagram, an iterate table and a log error plot; Newton's failures (flat tangents, cycles, divergence), basins of attraction, the complex z³ − 1 fractal, and Babylonian square roots digit by digit.

Sampling and simulation Watch probability and statistics happen: the central limit theorem from any distribution (even one you draw), the law of large numbers, confidence-interval coverage, A/B test planning and the cost of peeking, the bootstrap, permutation tests, Simpson's paradox, multiple comparisons, Monty Hall, two-dice events, balls into bins, coupons, inverse-transform and reservoir sampling — all on a seeded generator, so every picture can be linked.

Sets, relations and quantifiers Paint a three-set Venn diagram from an expression (or find the expression from a painting), linked to its truth table, with inclusion–exclusion counts; explore relations on up to eight dots — reflexive, symmetric, antisymmetric and transitive with witnesses, closures, equivalence classes and Hasse diagrams; and play the ∀∃ against ∃∀ game over a finite domain.

Spaced-repetition flashcards Flashcards for Mathematics, Reconnected, Human Biology for the Medical Maker and the AI Acceleration primer — definitions, formulas, mastery checks and glossaries, each linked to its chapter — plus Big-O and coding interview decks that go with this site's tools — scheduled with FSRS (or SM-2), with cloze cards, your own decks, CSV and Anki import and export, and statistics, kept in your browser.

Statistics Paste data and get descriptive statistics, histograms and box plots, regression with R² and residuals, correlation matrices, distribution calculators, and hypothesis tests with plain-language results.

Surfaces, gradients and gradient descent Type f(x, y) and see a rotatable 3-D surface, contours and a heat map, linked; partial derivatives as slices; the gradient field and a directional-derivative dial; the tangent plane and its error; critical points classified by the Hessian; Lagrange multipliers with λ as a shadow price; a double integral as columns that refine; and an optimiser race of gradient descent, momentum and Adam.

Symbolic algebra A computer algebra system in the browser: simplify, expand, factor, solve equations and systems, differentiate, integrate, take limits and Taylor series, partial fractions, and substitution — with LaTeX output, a step history, and a plot.

The maths of machine learning The mathematics under machine learning, hands on — least squares with draggable points (residual squares, outliers, L1 vs L2, normal equations vs gradient descent and SGD), logistic regression and its cross-entropy bowl, a computation graph with forward and backward passes against dual numbers and finite differences, TF-IDF and BM25 search, entropy with a Huffman tree builder and KL divergence, and softmax temperature with an attention matrix.

Unit circle and waves Drag round the unit circle and watch it unwrap into sin and cos, with quadrants, reference angles and exact values; find every solution of sin x = k; see radians as arc length and sin θ/θ → 1; fit A sin(B(x − C)) + D to the book's daylight and tide data; watch simple harmonic motion as the shadow of circular motion; and aim a turret with atan, atan2, y-down screens and the degrees bug.

Vectors playground Drag vectors in 2-D or a rotatable 3-D view and watch sums, linear combinations, dot and cross products, norms and Lᵖ circles, span and linear independence, and change of basis update live — with every number beside the picture — and see why random directions in high dimensions are nearly perpendicular.

Where floating point bites Watch rounding error happen: the V-shaped error of forward, central and complex-step derivatives in float16, float32 and float64; the quadratic formula losing digits and its stable rewrite; (1 + 1/n)ⁿ collapsing to 1; summation order and Kahan's cash register; Horner versus naive evaluation; forward versus backward recurrences; an ill-conditioned 2×2 system; partial pivoting; and Runge's phenomenon.

Z3 solver playground Microsoft Research's Z3 SMT solver running in the page — an SMT-LIB editor with readable models, puzzles that show the SMT-LIB they generate (Sudoku, N-queens, SEND+MORE=MONEY, magic squares, job scheduling, exam timetabling), and a small C-like language for proving bit tricks and finding overflow bugs.

Woodworking

19 Bending wood · Board feet and lumber · Closet organiser · Cut list optimizer …

Bending wood Kerf spacing, depth and count for a radius (with the deflection test), bent laminations with ply thickness from each species' strength and stiffness, springback and form compensation, steam bending times and the tightest radius with and without a strap, and arcs from chord and rise for laying out forms — all drawn to scale.

Board feet and lumber Board feet and cubic metres, nominal versus actual sizes for dimensional lumber and hardwood sold in quarters, prices per board foot, linear foot, piece, or m³, a lumber list with waste factor and totals, and approximate weight.

Closet organiser Plan a reach-in or walk-in closet as sections — double hang, long hang, medium hang, shelves, drawers and shoe shelves — with rod heights from published closet guidance, rod and shoe capacity, elevations, plan and isometric, a cut list for the towers, shelves and drawer boxes, a shopping list, and install steps.

Cut list optimizer Lay out parts on sheet goods or boards with kerf, edge trim, grain direction, and materials; see each sheet drawn to scale, the waste, the cost, and export a CSV or a printable cut sheet.

Deck and pergola planner Joists, beams, posts and footings from the American Wood Council's DCA 6 span tables by species, grade and spacing, ledger fastener spacing, decking and guards, a framing plan, section and isometric, cut and shopping lists, build steps, and an optional pergola — a planning aid, not engineering.

Drawer boxes and cabinet doors Drawer box sizes from the opening and the slide maker's published clearances (Blum TANDEM and MOVENTO, Accuride 3832), joinery allowances and fronts; cabinet doors full overlay, half overlay or inset with reveals, Euro hinge cup boring and hinge count, and shaker rail, stile and panel sizes — with drawings, cut list, steps and a print view.

Epoxy and resin pour calculator How much epoxy a pour needs — rectangles, rounds, river tables, or an outline traced on a photo — minus embedded objects, split into part A and B by volume or weight, with layers, colourant, cure, and cost.

Epoxy pour planner Plan an epoxy pour from start to finish — volume from a river-table outline, a rectangle, a cylinder, or area × depth; mix by volume or weight; the product's maximum pour depth turned into pours and waits; waste, kits and cost; the melamine form with a cut list; plan, section and isometric drawings; and step-by-step instructions.

Finishes and paint How much finish to buy for a list of projects, shellac pound cuts and dilution, a stain colour mixer previewed on different woods, sanding progressions, and dry and recoat times.

French cleat tool wall Lay out a French cleat wall — size, cleat rows, spacing and bevel, screws into the studs or a plywood backer — and a library of holders (screwdriver rack, drill holder, shelf, bin, clamp rack, saw till), each with its own cut list, drawn in elevation, section and isometric, with a shopping list and build steps.

Furniture designer Design a bookcase, a base or wall cabinet carcass, or a workbench from its size, sheet thickness and joinery (screws, pocket screws, dados, rabbets) — joint allowances added to the cut lengths, back panel, fixed and adjustable shelves with shelf-pin holes, face frame, toe kick — with drawings, a side-panel layout, a cut list, sheet and board layouts and a shopping list from the cut list optimizer, shelf-sag checks and illustrated steps.

Garage shelving and tote rack designer Design 2x4 garage shelving — bays of tote rails (totes hang by the lip and slide out like drawers) and fixed plywood or OSB shelves, mixed per level, free-standing or screwed to the studs — with front, side and isometric drawings, a cut list, a shopping list packed by the cut list optimizer, span checks and illustrated build steps.

Joinery layout Dovetail spacing with a drawn layout and marking positions, box-joint finger counts, mortise-and-tenon proportions, dowel and Domino sizing and spacing, and drawbore offsets.

Shelf sag calculator How far a shelf sags under books or a point load, for solid woods and sheet goods by stiffness, with optional front and back stiffening strips, compared against the 0.02-inch-per-foot guideline, with a drawn deflection curve.

Stair stringer calculator Risers and treads from the total rise, checked against IRC R311.7 (and AWC DCA 6 for deck stairs) — stringer layout with the throat check, headroom and stairwell opening, side elevation, plan and isometric drawings, cut and shopping lists, build steps, and a 1:1 printable step template.

Wood movement How much a board or panel will swell and shrink across its width from species shrinkage coefficients and moisture change, flatsawn versus quartersawn, equilibrium moisture content from temperature and humidity, and gaps for panels, tops, and breadboards.

Wood species A searchable reference of 100+ hardwoods, softwoods and sheet goods — Janka hardness, density, radial, tangential and volumetric shrinkage, decay resistance, workability, gluing and finishing notes, health cautions, CITES and IUCN status, uses and substitutes — with a picker that ranks species for what you are making and a side-by-side comparison.

Wood turning Segmented turning from a vessel profile — rings by height, segments per ring, mitre angle, segment lengths and widths, strip length with kerf, a staggered brick pattern, feature rings, ring plans, a side view and a printable cut list — plus lathe speed by diameter, stave construction angles for straight and tapered vessels, and turning blanks from a log.

Woodworking angles and fractions A tape-measure fraction calculator, polygon frame miters, compound miters for splayed boxes, crown moulding angles, stair risers and treads, and arcs from chord and rise.

Metalworking

12 Bolt circle and hole patterns · Bolt torque and preload · Fits, tolerances, and threads · Gears, belts, and chains …

Bolt circle and hole patterns X/Y coordinates for bolt circles, partial arcs, rows, and grids — with a drawing, chord distances, CSV export, and a ready-to-run G81/G83/G73 drilling program.

Bolt torque and preload Tightening torque and clamp force for metric (coarse and fine) and UNC/UNF bolts in ISO, SAE, socket-head, and stainless grades — by nut factor or by thread and under-head friction — plus the preload a given torque really gives, and a table for the whole series.

Fits, tolerances, and threads ISO 286 hole and shaft limits computed from the standard — H7/g6, H7/k6, H7/p6 or any class to 500 mm — with clearance, transition or interference drawn as tolerance zones; a size-range table; the ANSI B4.1 classes; thread dimensions for metric, UNC/UNF, BSP and NPT; a thread identifier; ISO 273 clearance holes; and the IT grade your 3D printer really holds.

Gears, belts, and chains Involute spur gears with a live meshing preview, contact ratio and undercut checks, and SVG/DXF export; gear-train search for any ratio; and length, centre distance, and speed for timing belts (GT2, HTD, T, MXL, XL, L), V-belts, and roller chain.

Lathe and metal shop Change gears for screw cutting on any lathe — simple and compound trains from your own gear set, the 127-tooth gear for metric on an inch leadscrew, and the error in ppm — thread-cutting passes and the 29.5° compound, clean knurling diameters, taper turning and Morse tapers, hardening and tempering O1, A2, D2, W1, 1045 and 4140 with temper colours, and a casting calculator for shrinkage, metal to melt and crucible size.

Metal weight calculator Weight and cost of bar, tube, sheet, and structural shapes — round, square, hex, flat, tube, angle, channel, I-beam, tee — in 27 metals and plastics, plus steel, galvanised, stainless, and aluminium gauge tables.

Sheet-metal bending Bend allowance, bend deduction, and setbacks; K-factors from a material table or a test bend; multi-bend flat patterns with a drawn profile and bend-line positions; press-brake tonnage and V-die sizing.

Speeds and feeds Spindle speed, feed rate, chip load, metal removal rate, and power for milling (with radial chip thinning), turning, drilling and reaming, and tapping — 18 materials with HSS, carbide, and coated carbide.

Spring calculator Helical compression, extension, and torsion springs — rate, stresses with the Wahl and curvature factors, allowable stress from the wire's real strength, solid height, buckling, natural frequency, hook stress, arbor clearance, and coils for a target rate.

Taps, drills, and threads Tap drill sizes with % thread engagement for metric, UNC/UNF, BSP and NPT (cutting and forming taps); clearance holes, counterbores, and countersinks; a searchable number/letter/fractional/metric drill chart; pitch diameter and three-wire measurement.

Tube coping and mitre templates Wrap-around templates for coping (fish-mouthing) round tube onto round or box-section tube — any angle down to 15°, offset branches, and several branches into one node fitted against each other — cut to the inside, mean or outside diameter; mitres for round, square and rectangular tube; hole-saw sizes, notcher angle, offset and clocking for each pass; a 3-D preview; printed at real size (tiled PDF or print), SVG and DXF.

Welding settings and reference Starting settings for MIG, TIG, and stick welding by material and thickness; electrode class decoder; filler metal for same and dissimilar metals; heat input in kJ/mm; joint types and weld symbols.

CNC and 3D printing

40 2.5D CAM · 3-D printer farm dashboard · 3D print cost quoter · 3D print troubleshooter …

2.5D CAM Turn an SVG or DXF drawing into G-code for a CNC router — pockets (offset or zig-zag), inside / outside profiles with tabs and lead-ins, drilling with pecks, engraving and V-carving — with a tool library fed from the router chip-load table, GRBL / LinuxCNC / Marlin output, a 3-D toolpath preview, a material-removal simulation and a time estimate.

3-D printer farm dashboard One page for every Klipper (Moonraker), OctoPrint and Bambu Lab (LAN mode) printer on your network — state, job, progress, time left, layer, temperatures with a graph, webcam, filament, and for Bambu printers the AMS spools and decoded HMS messages — with pause, resume, cancel and start, alerts when a print finishes, fails or a printer sits idle, and a job queue. Through a small relay you run, directly, or as a simulated demo farm.

3D print cost quoter Quote 3D prints from the slicer's G-code (PrusaSlicer, OrcaSlicer, Bambu Studio, Cura), a sliced Bambu / Orca 3MF (one line per plate) or a model's volume — material and waste, electricity and heat-up, machine wear, failure allowance, setup and post-processing labour, extras, markup, a minimum charge and tax — with saved printer and material profiles and a printable quote.

3D print troubleshooter Find a 3D printing problem by what it looks like — stringing, warping, ringing, layer shifts, under-extrusion, resin failures and more — then work through its causes, most likely first, with the fix and a quick test for each.

3D printer calibration Extruder e-steps (Marlin) and rotation_distance (Klipper), belt and lead-screw steps/mm, flow from a single-wall print, scale compensation, Z offset from a measured first layer, pressure-advance and input-shaping notes, and for Bambu Studio / OrcaSlicer the flow dynamics K, flow ratio, max volumetric speed and retraction tests.

Anodizing and electroplating calculator Anodizing and electroplating numbers: current from current density and the part's area, anodizing time by the 720 rule and a Faraday estimate, Type II / III ranges, dye and seal notes; plating mass, thickness and time by Faraday's law for copper, nickel, zinc, tin, silver and gold; surface area from simple shapes or an STL — with the safety notes, and no cyanide.

Bambu 3MF inspector Open a Bambu Studio or OrcaSlicer .3mf or .gcode.3mf and see every plate — thumbnail, print time, filament per slot with colours in grams, metres and cost — the objects with their parts and modifiers, the printer, process and filament settings, and each plate's G-code, which opens in the G-code viewer or costs out in the filament job planner.

Bambu HMS and error codes Look up a Bambu Lab HMS code (XXXX_XXXX_XXXX_XXXX) or print error (XXXX_XXXX) and see it taken apart — module, AMS unit, part or slot, severity — with a short meaning and what to do for about 210 common codes, and a link to Bambu's wiki page. Paste a printer report and every code in it is decoded.

Bed mesh visualiser Paste a bed mesh from Klipper, Marlin (bilinear or UBL), Prusa G81, or printer.cfg and see it as a heatmap and a rotatable 3D surface, with flatness statistics, tilt from a plane fit, how far to turn each levelling screw, and a before/after comparison.

Box and enclosure maker Finger-jointed laser/CNC boxes with kerf compensation, dividers, and eight lids — including living, knuckle, side-pivot, and bought hinges with magnet catches — nested onto sheets as SVG or DXF; and 3D-printable enclosures with PCB standoffs, connector cut-outs, and a snap, friction, screw, or hinged lid (print-in-place, snap-fit, filament pin, flexure) as STL — with a 3D preview that opens the lid and flags collisions.

CNC router feeds and speeds Chip load by material and bit size → feed rate, plunge, stepdown, and stepover for router bits; trim-router speed-dial settings; and V-bit depth and width geometry.

DXF checker for laser and CNC Check a DXF before it goes to the laser or router — units and inch/mm mix-ups, open contours with their gap sizes, duplicate and overlapping lines, tiny segments, splines and ellipses, text that is not exploded, blocks, layers and colours, and features too small for the bit or kerf — then fix what can be fixed and export a clean R12 DXF or SVG.

Embroidery file viewer and converter Open a machine embroidery file (DST, PES, PEC, JEF, EXP, VP3, XXX) and see it stitched — stitch count, colours, trims, jumps, size, whether it fits your hoop, thread per colour and sewing time, a stitch-by-stitch replay — then recolour, rotate, mirror, scale or split long stitches and save it as DST, PES, JEF or EXP.

Filament and print cost How much filament is left on a spool, length ↔ weight for any material and diameter, the full cost of a print — material, electricity, wear, and failures — a job planner that reads a slicer's G-code and costs a batch across plates with labour, and a materials reference table.

Fusion 360 parameter tables Build a set of Fusion 360 user parameters with each expression checked the way Fusion reads it (units, functions, if()), a configurations table of variants, hole and shaft sizes for ISO fits or printed clearances, and export them as the CSV Fusion's Change Parameters dialog imports, a ParameterIO file, or a Python script.

G-code generators Generate CNC programs for surfacing, rectangular and circular pockets, drill patterns with pecking, and profile cut-outs with tabs — plus 3D-printer first-layer, retraction, and e-steps calibration programs — with a live preview.

G-code sender Stream G-code from the browser over Web Serial to a GRBL, grblHAL or FluidNC CNC router or laser, or a Marlin 3D printer — with jogging, work zero, overrides, a live toolpath preview, a bounds check, and a console.

G-code viewer and simulator See a CNC or 3D-printer G-code file in 3D — rapids, cuts, extrusion, travel — scrub through it, step layer by layer, and get dimensions, distances, a time estimate, filament, tools, and speeds.

Geodesic dome and polyhedron calculator Icosahedral geodesic domes 1V–6V (class I) — whole spheres, 3V 3/8 and 5/8, 2V/4V/6V halves, or any hub ring — with strut types, chord factors, lengths and counts, hub types and the angles at them, dihedral angles, floor size, height, surface and volume, panel templates (fabric seam allowance or ply edge bevels), a cut list packed into your stock lengths, and a 3-D preview coloured by strut; plus Platonic solids and the truncated icosahedron as fold-up lamp-shade templates.

Glaze chemistry calculator Glaze recipe ↔ unity molecular (Seger) formula with a cited materials database — Si:Al, flux balance, the Stull chart, Appen thermal expansion for crazing checks, cone 6 and cone 10 limit formulas, a target formula solved back into a recipe, batches, and line and triaxial blends.

Grid maker The full Gridfinity designer — every gridfinity-extended generator with all its parameters, and tool inserts with pockets traced from a photo of your tools (or drawn, or picked from a parametric parts catalogue), rendered by real OpenSCAD in your browser and exported as STL, 3MF, or SVG / DXF sheet layers for foam, plywood and MDF.

Kiln and firing calculator Orton cone chart at 15, 60 and 150 °C per hour; a firing-schedule builder with a graph, total time, cone reached and energy cost; clay shrinkage and absorption with size-to-make; plaster and water for moulds; and slip specific gravity, water to add and deflocculant.

Laser test patterns Power × speed test grids as GRBL G-code (settings and labels built in) or colour-coded SVG with a legend, a kerf comb and kerf calculator, a slot gauge for press-fit joints, and a focus (Z) ramp — for CO₂ and diode lasers.

Laser-cut patterns Living hinges (straight, wave, diamond, honeycomb, spiral, serpentine) with a bend-radius estimate and an animated bend; the saw-kerf bending formula; finger, T-slot, egg-crate and snap-fit joints with kerf compensation and fit; a press-fit coupon, kerf test, polygons, stars and gear outlines; and nesting on sheets — as SVG with LightBurn, xTool or Glowforge layer colours, or DXF R12.

Lithophane, relief and sign maker Turn a photo into a printable lithophane — flat, curved, a cylinder lamp shade, a globe band, a heart or a framed shape — with a backlit preview, or into an embossed relief; make raised or engraved signs and nameplates in Google Fonts with the layer to change filament at; and extrude an SVG into coloured solids. STL and 3MF out, closed and manifold.

Mesh repair Fix STL, 3MF and OBJ models that are not closed solids — weld, clean, remove debris, orient, split non-manifold edges, stitch slits, fill holes, union overlapping shells, or rebuild by voxel remesh — with the problems shown in 3-D, a step-by-step report, a before/after deviation map, and a hand-over to the mold maker and model splitter.

Model splitter Split a model that is too big for your printer into pieces that fit — suggested cuts (fewest pieces, small seams, no slivers, little support, cuts at narrow waists) or your own planes placed with a gizmo — with pins, keys, dovetails, a lip, magnets or bolts on the cut faces, every piece laid flat and numbered, and STL / 3MF plates plus an assembly README.

Mold maker Turn an STL, 3MF, OBJ or STEP part into what you need to cast it — pick the process first: a printed rigid mould (automatic parting, keys, sprue, risers, vents, bolts, inserts), a silicone mould (a fitted pour box, a printed master, or brush-on silicone in a printed mother mould), a plaster slip-casting mould with printable case moulds, or a metal-casting pattern (lost-PLA investment pattern with sprue, feeder and flask, or a split sand pattern with match plate and core box) — with step-by-step instructions and quantities, exported as STL, 3MF, OBJ, STEP and DXF, laid flat on your printer's bed.

Motion hardware Size the moving parts of a printer, CNC or robot — closed-loop and open timing belts (GT2/GT3/HTD/T5/MXL), lead and ball screws (efficiency, back-driving, torque, critical speed, buckling), DC motors and gearbox ratios from Kt/Kv and stall figures, hobby servo torque at an arm, and whether an axis will move at your acceleration.

OpenSCAD in the browser Write OpenSCAD code and render it right in the page — the real OpenSCAD engine compiled to WebAssembly — with a 3D preview, a Customizer built from your parameter comments, BOSL2 and MCAD libraries on demand, and STL, 3MF, OBJ, OFF, AMF, SVG and DXF downloads.

Parametric parts Printable parts from a few numbers — Gridfinity bins and drawer-filling baseplates to the spec, PCB enclosures from a size or a KiCad / DXF outline (standoffs, snap / screw / sliding lids, USB-C, RJ45 and other cut-outs, vents, lid text), knobs for D, knurled and round shafts, ISO and UNC/UNF threads with print clearance, nuts, bolts and screw-lid boxes — previewed in 3-D and exported as STL, 3MF or STEP.

Post-processor G-code checker Paste or open a CNC program posted from Fusion and check it against the controller it will run on — GRBL, grblHAL, Marlin, LinuxCNC or a Haas/Fanuc-style mill: unsupported codes, arcs it will reject, modal state the program relies on, feeds of zero, cutting with the spindle off, fast plunges, low rapids, moves past the machine's travel, and a run-time estimate.

Print tolerances and fits Hole and peg sizes for press, snug, sliding, and free fits by process (FDM, resin, SLS), slicer compensation fitted from a measured test print, a downloadable clearance test (STL and OpenSCAD), and hole sizes for heat-set inserts, screws, and nut traps.

Sheet nesting for laser, CNC and plasma Nest DXF and SVG parts (or built-in shapes) true-shape onto sheets and remnants — quantities, gap and kerf, rotations, mirroring, grain lock, small parts inside holes — with a genetic search you can stop at any time, utilisation and cut length, and each sheet exported as SVG or R12 DXF with the original arcs.

Stained glass and mosaic pattern maker Turn a photo into a stained-glass pattern whose pieces you can actually cut — a minimum size and width, no deep inside curves or holes — with smooth lead or foil lines, numbered pieces and a colour key, glass area per colour with waste, came and foil lengths, an editor to merge, split, move and recolour pieces, and a real-size cartoon plus a pattern copy drawn at the pattern-shear width; or into a mosaic of square tesserae (grid, brick or following the edges) in your own tile colours, with counts and a printable map.

STEP and IGES viewer Open a STEP, IGES or BREP file in the browser — the assembly tree with each part's visibility and colour, measuring (distances, CAD edge lengths, hole diameters from round edges, face areas), a section plane, an exploded view, size, volume and mass — and export STL or GLB, or hand parts to the mesh tools.

Stepper motors Steps per mm for belts, lead screws, and gear reductions with microstepping; the resolution you can rely on; the reference voltage for A4988, DRV8825, and TMC2208/2209 drivers; and a corner-speed and step-rate check against your controller.

STL, OBJ, and 3MF viewer and analyser Open a 3D model to check its size, volume, surface area, and whether it is watertight; estimate print weight and cost; scale, rotate, mirror, or flip it; and export STL.

Vinyl cutter helper Text in a Google Font or an SVG, ready for a vinyl cutter — weeding box and weeding lines, a contour outline for stickers, mirroring for HTV, a layer per colour with registration marks, drag-knife blade offset with corner swivels and overcut, tiling across the roll — exported as SVG or HPGL, or sent straight to a USB-serial cutter.

X-Carve setup and GRBL settings Every GRBL $-setting for an X-Carve (500/750/1000 mm, X-Carve Pro), a Shapeoko or a generic GRBL router, computed and explained, compared with your controller's $$ and written back one at a time — plus calibration: steps/mm, squaring, tram, switches, touch plate, spoilboard surfacing and bit feeds.

Resin

5 Candle and soap calculator · Concrete, GFRC, plaster and Jesmonite casting · Foundry: metal casting calculator · Resin casting calculator …

Candle and soap calculator Candles: wax, fragrance and dye for a jar, tin or pillar mould by wax type (soy, paraffin, beeswax, coconut, palm, gel), pouring temperatures, cure time, a wick band by diameter and the burn test. Soap: a lye calculator with 36 oils and fats — NaOH or KOH, superfat, water by concentration, ratio or % of oils, recipe in grams, ounces and per cent, batch sized to a mould, quality numbers from fatty-acid profiles, fragrance, and lye safety.

Concrete, GFRC, plaster and Jesmonite casting Mix and bag counts for cast concrete and its relatives — volume from a countertop with a sink cut-out, a round or square planter, a sphere, a block or an STL — with mix designs by weight and volume for concrete, mortar, wet-cast countertop mix, GFRC face and backer coats, hypertufa, gypsum plasters by consistency, Jesmonite AC100 and Forton MG; water and water/cement ratio, US and UK bags, pigment loading, reinforcement, a strength curve, release agents for each mould material, sealers and a printable plan.

Foundry: metal casting calculator Metal casting for a hobby foundry — an alloys table with pouring temperatures, shrink and hazards; metal needed from a volume, an STL or a pattern's weight (the wax-to-metal rule) with crucible size and number of melts; sand-casting allowances, Bernoulli choke area, pouring time, gating ratios and Chvorinov risers, flask and sand mix; investment powder and water and wax or PLA burnout schedules on a graph; lost foam; the energy, fuel and time to melt; a crucible-furnace build; and a printable safety checklist.

Resin casting calculator Resin for parts cast in a mould — volume from a shape, an STL, water displacement or a fill test, minus inserts; polyurethane, epoxy, UV and polyester classes with A and B by weight and volume; cold casting with metal or stone powder by weight and by volume; fillers and pigment; per part, per batch, kits and cost per part; how many moulds one mix fills before it gels; cure time against temperature; exotherm and shrinkage checks; slush and rotational shells; and a printable plan.

Silicone and urethane mould making How much rubber a mould takes — one- and two-part block moulds, cut moulds, brush-on glove moulds and poured blanket moulds, from the part's size, a shape or an STL — with A and B by weight and volume, pot life and demould times, an inhibition checker, release agents for each pair of materials, degassing and pressure notes, mother mould materials, and a printable step list.

Makerspace

6 Laser and CNC materials library · Machine booking calendar · Machine inductions and sign-offs · Machine QR cards …

Laser and CNC materials library Is it safe to cut? A materials table for CO₂, diode and fibre lasers and CNC routers with the reason for each rating, how to identify an unknown plastic without burning it, and a settings library per machine — starting points for 40–80 W CO₂ and 5–20 W diode lasers, scaling by wattage, JSON, CSV and LightBurn .clb export, and printable test cards.

Machine booking calendar Book the laser, the printers and the CNC at a makerspace — day and week views, drag to book, opening hours, slot length, longest booking and a gap between bookings per machine, clashes refused, repeating maintenance blocks, who's on now and next, a printable day sheet for the door, and .ics in and out. Runs on one shared tablet; sync another device by file.

Machine inductions and sign-offs Induct members on a makerspace's machines — a checklist the inductor ticks with them, a shuffled quiz with a pass mark, and a dated sign-off that expires when the machine says — with a register of who is signed off on what, expiring and expired sign-offs, CSV export, printable sign-off cards and member passports, a machine page for QR codes, and an editor for the space file.

Machine QR cards Printable safety cards and posters for each machine in a makerspace — A4 and A5 posters, A6 cards four to a sheet, or small Niimbot labels — with ISO 7010-style signs for PPE, hazards and rules, allowed and banned materials, key settings, who to ask, and a QR code that opens the machine's page and induction.

Project cost quote Price a job for a member or a customer — sheet goods by area, filament and resin by weight, consumables, machine time at each machine's member and non-member rate (the laser estimated from cut length and speed), labour, design time, setup, waste and markup, discount, VAT or sales tax and a deposit — and print the quote with its line items and terms. Saved quotes, duplicates, any currency.

Tool library checkout A lending desk for a makerspace's tool library — a catalogue with asset tags, check out by scanning the tool's QR code or typing its tag, due dates in the space's time zone, returns with a condition note, an overdue list, history per tool and per member, asset tags for the label maker and a QR sheet. Runs on one shared tablet; sync another device by file.

Workshop services

4 Compressed air sizing · Dust collection planner · Sharpening angles · Shop power planner

Compressed air sizing Size a shop's compressed air: the SCFM your tools need with their duty cycles, your compressor against it with tank pump-down and recovery times and starts per hour, pipe pressure drop for copper, black iron, aluminium or PEX-AL-PEX (Darcy–Weisbach and a rule of thumb), how much water the air drops and its dew point, and the motor's current and circuit.

Dust collection planner Lay out a dust-collection duct system as a tree — mains, branches and machines with their recommended airflow — and see the air speed in every run, the static-pressure loss from friction (Darcy–Weisbach with Colebrook) and fittings, the worst machine with one or two gates open, and the operating point where the system curve meets your collector's fan curve.

Sharpening angles Primary and micro-bevel angles for chisels, plane irons, gouges, knives, axes, scissors and drills by steel (O1, A2, PM-V11, D2, HSS, carbon, VG-10, stainless); a honing-guide projection calculator with the geometry derived and calibration from your guide's chart; a printable projection jig and laser-cut angle gauge (SVG and DXF); JIS / FEPA / micron grit conversion; and knife-sharpener rod angles.

Shop power planner Plan a workshop's circuits — US 120/240 V split-phase or UK/EU 230/400 V three-phase — with breakers, wire and run lengths, and the machines on each (table saws, dust collectors, compressors, welders, kilns, lasers, 3-D printers, heaters, lights): what can run at once under the 80 % continuous rule, which motor starts will trip the breaker, voltage drop running and on start, three-phase currents, and a load schedule to print. A planning aid, not a substitute for an electrician.

Camera and sensors

6 Bluetooth sensor dashboard and trainer control · Compass and level · Measure from a photo · Phone seismograph …

Bluetooth sensor dashboard and trainer control Connect several Bluetooth sensors at once — heart-rate straps, power meters, speed and cadence sensors, running pods, smart trainers, thermometers, Xiaomi LYWSD03MMC, scales — with big live numbers and graphs, one timeline logged in the browser and exported as CSV, and ERG workouts and free rides on an FTMS trainer.

Compass and level Your phone as a compass — magnetic or true north, with the declination worked out for where you are by the World Magnetic Model — and a spirit level: a bullseye for flat surfaces, a tube for edges, two-sided calibration, a target angle that beeps, and the slope in degrees, percent, inches per foot and mm per metre.

Measure from a photo Photograph something next to a bank card or a sheet of paper, drag four handles onto the reference, and measure lengths, rectangles, and areas on that surface — perspective-corrected, with a magnifier, pinch-zoom, undo, and an annotated PNG to save.

Phone seismograph Your phone's accelerometer as a seismograph: a live three-axis trace with gravity and tilt filtered out, a helicorder (drum) view, an STA/LTA trigger with an event log, peak ground acceleration in g with the approximate Modified Mercalli intensity, a spectrum to see what is shaking (footsteps, a washing machine), and recordings saved as CSV or WAV. A demo mode makes synthetic earthquakes on a desktop.

See it on your wall Photograph a wall, then lay pictures, a TV, a shelf, or a photo of furniture over it — moved, scaled, pinned by four corners onto an angled wall, or placed at its true size by measuring against a sheet of paper or a door in the shot.

Sensor data logger Log a sensor for a science project from an Arduino, ESP32, Pico or micro:bit over USB (Web Serial) or Bluetooth, or from a simulated source: CSV, name:value, JSON and Serial Plotter lines plotted live with zoom and scroll, markers, per-channel statistics, units and calibration, the sample rate, recordings saved in your browser, CSV/JSON export, and example programs to copy.

Photography

9 Depth of field and lenses · EXIF statistics: how you shoot · Exposure calculator · Film development timer …

Depth of field and lenses Depth of field with near and far limits, hyperfocal distance and a diagram; circle of confusion by sensor from phones to 4×5; two set-ups side by side; field of view and framing; equivalent focal length, aperture and ISO across formats; megapixels for a print; diffraction against pixel pitch; and macro with extension tubes.

EXIF statistics: how you shoot Drop a folder of photos — JPEG, HEIC, DNG or camera RAW — and see which focal lengths, apertures, shutter speeds and ISOs you really use, which lenses and cameras, and when you shoot; export the table as CSV. Read in your browser; nothing is uploaded.

Exposure calculator The exposure triangle with EV at ISO 100 — lock any two of aperture, shutter and ISO and see the third — plus stops arithmetic in ⅓ and ½ stops, Sunny 16 and a light-level table, ND filters with a long-exposure countdown, reciprocity failure for film, and the shutter speed that freezes a moving subject or a shaky hand.

Film development timer Film + developer + dilution + EI → development time from Ilford and Kodak datasheets, corrected for temperature and continuous agitation, with push and pull; your own combinations; and a step timer for pre-soak, developer with agitation prompts, stop, fix and the Ilford wash, with sound and vibration — plus C-41 and E-6.

Flash calculator Guide number, distance, aperture and ISO solved from any three; flash power in ⅓ stops from 1/1 to 1/128; inverse-square falloff to the background; several flashes together; the light lost to high-speed sync, with flash balanced against the ambient; and key:fill lighting ratios, softbox size and distance, and a top-down diagram of where the lights go.

Night-sky photography The longest shutter speed for pinpoint stars — the 500 rule against the NPF rule, from your sensor's pixel pitch, aperture, focal length and where you point — a star-trail planner (frames, gaps, total time, arc swept, card space), and when the Milky Way's core is up in a dark sky, tonight and through the year.

Print size and DPI Pixels ↔ print size at any ppi; the resolution the eye can use at a viewing distance (1 arcminute acuity); a photo cropped to a paper's shape with an overlay on your own image; how much upscaling a print needs; and mat window, borders and the standard frame that fits.

Sun and moon planner Plan the light for a place and date: sunrise and sunset, golden and blue hour, civil, nautical and astronomical twilight, the sun's azimuth and elevation through the day, and moonrise, moonset, phase and illumination — with a day chart and a sky compass, in the place's own time zone.

Timelapse planner Event duration ↔ clip length ↔ interval at your frame rate; frames, card space and batteries; shutter angle and the ND filter for natural motion blur; and a day-to-night exposure ramp laid over the real sunset and twilight times for a place and date.

Bikes and cycling

5 Bike gearing calculator · Bike maintenance log · Bike tyre pressure · Cycling power, climbing and zones …

Bike gearing calculator Gear inches, development, gain ratio and speed at any cadence for chainrings × cassette (or an internal hub) on your wheel and tyre; compare two drivetrains gear by gear with their steps; cross-chaining warnings; and a chain-length estimate.

Bike maintenance log A wear and service log for your bikes: parts with install date and distance, rides typed in or imported from GPX, FIT or CSV, reminders by distance and time, chain-stretch checks against the 0.5% / 0.75% rule, service history and costs — kept in your browser, with JSON backup.

Bike tyre pressure Starting front and rear tyre pressures from your weight, the bike, the weight split, tyre width, construction and surface — from Frank Berto's 15% tyre-drop measurements, with every step of the working shown and the rim and tyre limits applied.

Cycling power, climbing and zones Power for a speed and speed for a power — with position (CdA), surface (Crr), gradient, wind, air density from altitude and temperature, and drivetrain loss; the time for a climb, VAM and W/kg; energy; and Coggan power and heart-rate training zones from FTP and LTHR.

Spoke length calculator Spoke lengths for each side of a wheel from the rim's ERD, the hub's flange diameters and centre-to-flange distances, spoke count, lacing and hole size — with rounding advice, bracing angles, the left/right tension ratio, rim offset, and an ERD-from-measurement helper.

Cooking and baking

17 Artisan bread · Baking ratios and substitutions · BBQ cook planner · Bread and baker's percentages …

Artisan bread A bake-day studio for bread: a library of about ninety breads from pain de campagne to injera, bagels and panettone — each with its formula, timed process, techniques, shaping and bake — a sourdough tab (starter types, a bulk-time model with the aliquot target, converting recipes to and from sourdough, rye sours, discard), braid, bagel, pretzel and pita drawings, hearth-style formulas from baguette to 100 % rye, preferments worked out from a straight dough (poolish, biga, pâte fermentée, levain, scalds) with their timing by temperature, a printable bake-day plan with fold timers and an aliquot-jar bulk target, shaping and scoring drawings, steam and oven set-ups, crumb troubleshooting and a flour guide.

Baking ratios and substitutions Classic baking ratios by weight as sliders that give the whole recipe in grams for any batch, with what each ingredient does and what pushing it changes; substitutions for eggs, dairy, sugars, fats, chocolate, flours, leaveners and yeast with their adjustments; high-altitude changes by elevation; and a check of the baking powder, soda and acid in a recipe.

BBQ cook planner Plan a smoker cook: meats and weights give estimated cook-time ranges at your pit temperature (rules of thumb — the probe decides), the stall and when to wrap, rest and hold; a timeline worked back from dinner across all the meats and the smoker's space; live alarms; and the USDA FSIS safe temperatures kept apart from quality targets like 203 °F brisket.

Bread and baker's percentages Write a bread formula in baker's percentages and get grams for any number and size of loaves, with the true hydration (counting the levain and the water in milk, eggs and butter), yeast conversions and a time-and-temperature rule of thumb, and the water temperature for your desired dough temperature.

Brines and cures Dry cures and equilibrium brines by weight: Cure #1 or Cure #2 dosed to a nitrite target in ppm and never above the US limit for the product, salt and sugar by weight with the salt in the cure subtracted, presets for bacon, ham, corned beef, pastrami, sausage, dry-cured whole muscle and gravlax — plus plain brines by strength — with safety notes and sources.

Cake pans and batter Move a cake recipe to another pan shape or size by batter volume — with the fill depth, a bake time scaled from the batter's thickness, the oven temperature and doneness tests — and plan layer and tiered cakes, frosting, filling and ganache, with a table of standard US and metric pans.

Coffee brewing calculator Coffee-to-water ratios per brewing method, a recipe timer that calls out each pour with the weight the scale should read, and the extraction yield from a TDS reading, plotted on the SCA brewing control chart with brew-ratio lines.

Fermentation salt and timing Salt by weight for a ferment three ways — % of the vegetables (dry-salted kraut), % of the brine, or % of everything including the water — with the NCHFP's tested sauerkraut and dill-pickle proportions as percentages, NCHFP fermentation times by temperature with calendar check-ins, and a batch log of pH readings against the 4.6 line.

Home bar Tick the bottles and ingredients you have and see which of 200-odd classic, tiki, low-ABV and alcohol-free drinks you can make now and which are one or two away; rank the next bottle by how many drinks it unlocks; scale or party-batch any drink with dilution water, with its strength in standard drinks; syrup recipes, favourites and notes.

Home canning times Tested home-canning processes only: pick a product from the USDA Complete Guide to Home Canning as published by the NCHFP, your canner (boiling water, dial or weighted gauge), jar, pack and elevation, and read the process time and pressure exactly as published — with the whole table, the recipe's own page, and plain warnings about untested recipes and low-acid foods in boiling water.

Homebrew calculator All-grain and extract beer recipes: OG, FG and ABV, IBU by Tinseth or Rager, colour by Morey with a swatch, mash and sparge volumes and strike temperature, efficiency and attenuation from your readings, priming sugar and keg pressure, and brewing-salt additions toward a water profile with an approximate mash pH.

Kitchen conversions Cups and spoons to grams by ingredient from a cited density table (with Diamond Crystal, Morton kosher and table salt kept apart), oven temperatures in °C, °F, gas mark and fan, sugar stages, butter sticks, egg sizes in the US, EU/UK and Canada, and pan areas and volumes.

Meal timing planner List the dishes with their prep, cook and rest steps and oven temperatures, say when to serve, and get a timeline of when to start each step — with oven-clash hints and preheat reminders — then run it live with alarms, notifications and the screen kept on. Plans are saved in your browser, with JSON export and import.

Pastry lab Plan laminated doughs — croissant, pain au chocolat, Danish and puff — with the butter block and détrempe, each fold's roll size and the layers drawn, butter temperatures and croissant cutting sizes; process cards for choux, meringues, custards, curd and caramel; sugar stages at your altitude with an Italian meringue syrup planner; chocolate tempering curves with a step timer; and shortcrust sized to your tart tin.

Pizza dough Pizza dough for any number of balls or pans by style — Neapolitan, New York, Detroit, Roman tonda and teglia — with hydration, salt, oil and sugar, the yeast worked out for same-day, 24-hour or 48–72-hour cold fermentation, an optional poolish or biga, and oven notes.

Sourdough starter and levain planner Feed a sourdough starter at any ratio, build exactly the levain a recipe needs (counting the starter's own water), estimate when it will peak at your kitchen's temperature — calibrated to your starter — and plan bake day backwards from when the loaf goes in the oven, with a printable timeline, calendar file and reminders.

Sous-vide and roasting Doneness and USDA safe temperatures; sous-vide heating, pasteurisation and cooling times by thickness from Douglas Baldwin's published tables; FDA and FSIS core-temperature hold times; and roasting time estimates from the USDA FSIS timetables, with carry-over cooking — and the thermometer as the judge.

Astronomy

7 Eclipses and meteor showers · Observing planner · Planet details · Planet events and alignments …

Eclipses and meteor showers Every solar and lunar eclipse from 2020 to 2050 with its times and how much you'll see from your place — contacts, magnitude, obscuration, the path of totality on a world map — and the meteor showers of the IMO list, with the rate you can expect tonight after the radiant's height, your sky and the moon.

Observing planner What's worth looking at tonight: the Messier and Caldwell objects and some showpiece stars ranked for your place, sky and telescope through the dark hours, each with an altitude chart; the night's cloud, transparency and dew forecast; a saved observing list, a session log you can download, and the Messier marathon's best night and running order.

Planet details The planets in your eyepiece, drawn to scale at your magnification and flipped the way your telescope shows them: Jupiter's four big moons and their transits, shadows, eclipses and occultations, and when the Great Red Spot crosses; Saturn's ring tilt and its moons; Mars's central meridian and markings; Venus's and Mercury's phases.

Planet events and alignments Conjunctions of planets with each other, the Moon and bright stars, planet "parades", oppositions, greatest elongations, stations and retrograde loops, Mars's closest approach and lunar occultations — for the next year or twenty, filtered to what you can actually see from your place, each with a picture of the sky at the best moment and an .ics file for your calendar.

Sky darkness Convert between the Bortle class, sky brightness in mag/arcsec² (an SQM reading), naked-eye limiting magnitude and how much brighter than natural your sky is; see what each class shows and a simulated star field at that darkness; and estimate tonight's limiting magnitude by altitude with the Moon up.

Sky tonight A star chart for your place and time — the whole sky as a dome or a zoomable view, with stars to magnitude 6.5, constellations, the Milky Way, Messier objects, the planets and the Moon's phase; a time slider, search, rise/transit/set for anything you tap, a red night mode, and a mode that shows what your phone is pointing at.

Telescope mount Polar alignment (where Polaris or σ Octantis sits on your polar-scope reticle right now, and drift alignment), setting circles (RA/Dec to altitude and azimuth and back, hour angle, sidereal time), and a GoTo controller over Web Serial for Celestron NexStar, Sky-Watcher SynScan and Meade LX200 mounts — connect, read where it points, slew, sync, nudge and stop. It refuses to slew near the Sun.

RC planes

8 Can I fly? · FPV channel planner · FPV quad: build, rates, CLI diff and blackbox · LiPo manager …

Can I fly? For your flying fields: the hourly forecast — wind and gusts at 10 m and the wind at 80 and 120 m, rain, cloud and an estimated cloud base, visibility, temperature — and the geomagnetic Kp index, judged against each aircraft's limits as a go / marginal / no timeline for 48 hours or 7 days, with the reasons, the best windows and the runway crosswind.

FPV channel planner Choose 5.8 GHz video channels for a group of pilots — analogue bands, HDZero, DJI and Walksnail — keeping them apart and away from intermodulation products, with a frequency table and a range estimate for video and ExpressLRS links.

FPV quad: build, rates, CLI diff and blackbox Plan a quad build (all-up weight, thrust-to-weight, hover throttle, flight time, prop clearance), compare and convert Betaflight rates and test them with your transmitter, diff two Betaflight CLI dumps into a script, and open a blackbox log to plot gyro, PIDs and motors with a noise spectrum.

LiPo manager Keep a register of your LiPo packs — cells, capacity, C rating, chemistry, age, cycles, and internal resistance over time on a chart — with a quick log after each charge or flight, warnings for rising IR, out-of-balance cells, old and puffed packs, calculators for charge current and time, storage voltage, parallel charging and airline watt-hour limits, and QR labels that open a pack's record.

Model plane designer Design a model plane's wing: straight, tapered, swept, multi-panel, delta or flying-wing planforms → area, aspect ratio, MAC drawn on the planform, neutral point with the tail, CG range by static margin, wing and cube loading, stall speed; NACA 4/5-digit or pasted .dat airfoils; laser-cut ribs with spar notches, sheeting and lightening holes as SVG, DXF or a 1:1 PDF.

RC car gearing and setup sheets Pinion and spur to final drive ratio, rollout and theoretical top speed from Kv or motor turns; a pinion × spur table with a target highlighted; gear mesh centre distance against the motor-mount slot; shock oil, diff oil and spring rate conversions; and setup sheets per car that you can compare, export and print.

RC power setup — motor, prop and battery Work out what a motor, propeller and LiPo will do together — RPM, current, voltage sag, power, efficiency, static thrust, pitch speed, thrust-to-weight, hover or cruise throttle and flight time — with warnings for the motor, ESC and battery, a throttle sweep chart and up to three setups side by side.

Servo and control surfaces Servo arm, horn and hinge offset → surface throw in degrees and mm at the trailing edge (solved exactly, with a linkage drawing), and the arm or horn for a target throw; end points, rates and expo curves; elevon, V-tail, flaperon and crow mixes shown live from sliders or a USB transmitter; and the servo torque a surface needs.

US electrical

11 Available fault current (point-to-point) · Box fill (314.16) · Conduit bending · Conduit fill (Chapter 9) …

Available fault current (point-to-point) Available fault current by the point-to-point method — transformer or utility figure, then conductor runs — with the formulas shown, motor contribution, and a check against equipment ratings (110.9, 110.10, 110.24).

Box fill (314.16) Count a box's fill the NEC 2023 way (314.16): pick a metal box from Table 314.16(A) or enter a plastic box's marked volume, add conductors by size, loops, clamps, studs, devices and grounds with big +/− buttons, and see the cubic inches needed against the box, with a bar and the boxes that would fit.

Conduit bending Conduit bending marks for offsets, rolling offsets, saddles, 90° stubs, back-to-back 90s, kicks, segment bends and parallel offsets — drawn to scale, in inches to 1/16, with the 360° rule between pull points.

Conduit fill (Chapter 9) Conduit fill by NEC 2023 Chapter 9: choose the raceway (EMT, IMC, RMC, PVC 40/80, ENT, FMC, LFMC, LFNC…) and add conductors by insulation and size — the fill against 53, 31 or 40 % (60 % for a nipple), the smallest trade size of each type, a drawing of the cross-section, the jam ratio for three conductors, and an Annex C-style table of how many fit.

Dwelling service load calculation What service a one-family house needs under NEC Article 220: standard and optional methods, an existing house adding an EV charger or heat pump, the neutral, and a printable step-by-step worksheet like the Annex D examples.

Electrician's quick reference A searchable phone cheat sheet: US wire colours (incl. 277/480 V), NEMA receptacle faces and ratings, GFCI and AFCI locations, working space, breaker/wire pairings and torque.

Grounding and bonding sizes Size the grounding and bonding conductors by NEC 2023 Article 250: the equipment grounding conductor from the breaker (Table 250.122, upsized in proportion when the hots are upsized), the grounding electrode conductor from the service conductors (Table 250.66) with the rod, concrete-encased and ring limits, and the main, system and supply-side bonding jumpers (Table 250.102(C)(1) and the 12.5 % rule) — each with what it does and why.

Motor branch circuit (Article 430) Size a motor circuit by NEC Article 430: full-load current, conductors, breaker or fuses by Table 430.52, overloads, disconnect, grounding conductor, starting kVA and voltage dip, a feeder for several motors, and a one-line summary card.

Panel schedule and load balancing Lay out and balance a 120/240 V, 208Y/120 V or 480Y/277 V panel: circuits, poles and breakers, per-phase VA, amps and neutral, imbalance, demand against the main, checks, and a printable schedule or CSV.

Transformers and three-phase Transformer kVA and amps, 450.3(B) protection, 240.21(C) secondary conductors, buck-boost selection with a wiring diagram, delta/wye and the high-leg delta, and the power triangle with PF correction.

Wire size and voltage drop The smallest US conductor (NEC 2023) for a load, rule by rule — 125 % of continuous load at the terminations, ambient and bundling corrections, the breaker it must be protected by, the 14/12/10 AWG limits, parallel sets — and voltage drop by the K-factor or Chapter 9 Table 9 method, with the rule that governs highlighted. Or the reverse: what a given wire will carry and how far.

Building trades

7 Drywall, paint and tile · Framing and roofing · Gas pipe sizing · HVAC ducts and airflow …

Drywall, paint and tile Plan a tiled floor or wall to scale — straight, ½ or ⅓ offset, herringbone or diagonal — with the layout shifted to avoid slivers, every cut size, the starting lines to snap, tiles and boxes, thinset and grout; plus drywall sheets chosen for the fewest butt joints with screws, mud and tape, paint by surface and coat, and plank or sheet flooring.

Framing and roofing Roof pitch ↔ angle ↔ rise/run; common, hip, valley and jack rafters with the birdsmouth, ridge reduction and speed-square marks drawn to scale; gable studs; rafter, ceiling-joist and header sizes from the IRC span tables; a stud-by-stud wall take-off with headers; and shingles, sheathing, underlayment, drip edge and ridge cap for the roof.

Gas pipe sizing Draw a tree of gas pipe sections and appliances and get a size for every section — natural gas or propane, schedule 40 steel, CSST, copper or polyethylene, at the usual supply pressures, by the longest-length or branch-length method — computed from the IFGC/NFPA 54 sizing equations and held at or under the code's tables, with the pressure left at each appliance and a capacity table laid out like the code's.

HVAC ducts and airflow Airflow from heating and cooling loads, room airflow in proportion to room loads (imported from the heat-loss tool if you like), trunk-and-branch duct sizing by the equal-friction method in the manner of Manual D, round and rectangular sizes, velocities, registers and grilles, the static-pressure budget and a fan-curve check — with the layout drawn.

Pipe offsets and takeoffs Pipefitting arithmetic: set, run and travel for 11¼° to 90° offsets, rolling offsets drawn as a box, parallel pipes through an offset or round a corner, cut lengths from centre-to-centre measurements less fitting takeoffs (copper, PVC/ABS DWV, threaded steel, PEX), drain slope over a run, and the volume and weight of a pipe full of water — in inches to 1/16 with millimetres.

Plumbing sizing Size drains, stacks and building drains from drainage fixture units, vents by developed length, trap arms, drain slope, water supply pipe from fixture units (Hunter's curves, Hazen–Williams loss and the available-pressure method) and the water heater — by the 2021 IPC or the 2021 UPC, with each table cited.

Pumps, tanks and hot water Size a thermal expansion tank from the heater volume, temperatures and pressures; a well pressure tank for a minimum pump run time; a well pump's total dynamic head with its curve against the system curve; a hot-water recirculation pump's flow and head from the loop's heat loss; water-heater recovery and a rough first-hour figure for gas, electric and heat-pump heaters; and a tankless heater from flow and temperature rise.

Energy and off-grid

4 Generator sizing · Off-grid solar system sizing · RV and boat DC power · Solar ROI calculator

Generator sizing List what must run in an outage — fridge, well and sump pumps, furnace, AC and heat pump by tonnage, EV charger, lights, tools — with running watts and starting surge from the code letter or locked-rotor amps (and soft starters); find the start order with the lowest peak, the generator size after derating for altitude, heat and fuel, fuel per hour and runtime from your tank, leg balance, and what NEC 702 asks of the transfer switch.

Off-grid solar system sizing Size a stand-alone solar system from a list of what you run — cabin, van, boat or tiny house — and your location's month-by-month sunshine (Open-Meteo, or your own peak sun hours): the PV array for the worst month or the year, how to string the modules (cold Voc under the controller's limit, NEC 690.7; 1.25 × Isc, 690.8), MPPT or PWM, the LiFePO4 or lead-acid bank in series and parallel, the inverter, a month-by-month balance with generator hours, and a single-line diagram.

RV and boat DC power Plan the 12/24/48 V side of a camper van, RV or boat: wire size by voltage drop (3 % critical, 10 % non-critical, ABYC E-11 style) and ampacity with engine-room and bundling derates, the fuse that protects it and how close to the battery it must sit, a battery bank in series and parallel with balanced wiring and the main fuse its short-circuit current needs, alternator DC-DC and shore chargers, a busbar and fuse-block layout, and a daily amp-hour budget.

Solar ROI calculator Size a rooftop solar system from your electricity use and location, then see payback, NPV, IRR, the cost per kWh of solar energy, financing, and a year-by-year cash flow over its life.

Cars and EVs

8 12 V and 24 V vehicle wiring · Engine calculator · EV charging · OBD-II car diagnostics …

12 V and 24 V vehicle wiring Wire a car, van, truck or motorbike: cable size in mm² and AWG from the current, the round-trip length and the voltage drop you allow, with insulation rating, under-bonnet heat and bundling; the fuse that protects it; relay circuits drawn as schematics with the 30/85/86/87/87a pins and the flyback diode; crimp terminals and connectors; parked battery drain and the alternator's load; a second battery on a DC-DC charger; and the DIN 72552 terminal numbers.

Engine calculator Displacement from bore, stroke and cylinders; static and dynamic compression from the chamber, gasket, deck, piston and the cam's intake closing; rod ratio and piston speed; airflow and horsepower–torque; and gearing — speed at rpm in every gear with a shift chart, rpm at cruise, and which final drive to pick.

EV charging How long a charge takes and what it costs — Level 1, Level 2 or DC fast with a taper curve, the car's on-board charger limit, losses, flat or time-of-use prices — the range it adds per hour, the cost per mile against petrol, and the home charger circuit: 125 % breaker, wire size and receptacle under NEC 2023.

OBD-II car diagnostics Plug an ELM327 adapter into the car and read it from the browser over Bluetooth LE or USB — live gauges and graphs with CSV logging, stored, pending and permanent trouble codes with descriptions, the freeze frame, readiness monitors, the VIN, and clearing codes — or try it all on a simulated car.

Small engines Workshop sums for small petrol engines and more: two-stroke fuel mix in litres, gallons and fluid ounces; antifreeze strength and freezing point for ethylene and propylene glycol, and how much to drain to get there; rejetting a carburettor for altitude and temperature by air density; reading spark plugs and a compression test; identifying chainsaw chain by pitch, gauge and drive links; mower blade tip speed and belt length; displacement and power; and a seasonal maintenance and winter storage checklist.

Turbocharger matching Match a turbo to an engine: pressure ratio and corrected air flow (lb/min and kg/s) at every rpm plotted on an illustrative compressor map — or your own surge and choke lines — with surge and choke margins, compressor-outlet and intake temperatures and estimated power; the turbine side from the power balance (back-pressure, drive ratio, wastegate flow and size, A/R and twin-scroll notes); injectors and fuel pump for the power; and the intercooler.

Tyre size calculator Compare two car tyre sizes — metric, P- and LT-metric, or flotation like 33x12.50R15 — for diameter, width, sidewall and revs per mile, see the speedometer error at each speed and the ride-height change, draw them to scale, check rim widths, and work out wheel offset, backspacing, poke and inner clearance.

Vehicle log A log for your cars, vans and motorbikes: fuel-ups with economy worked out properly across partial fills (mpg US or UK, L/100 km, km/L), EV charging sessions and mi/kWh, service reminders by distance and time with overdue alerts, repairs and parts, cost of ownership per mile or km with charts — plus a VIN decoder (check digit, model year, maker, and an NHTSA vPIC lookup), JSON backup and CSV import and export.

Music and audio

6 Chords and scales explorer · Instrument tuner · MIDI monitor, controller and step sequencer · Piano and guitar trainer …

Chords and scales explorer Any scale or mode in any key on a piano and a guitar fretboard (any tuning, left-handed, CAGED and three-notes-per-string patterns), the key's chords with Roman numerals and functions, a chord namer that handles inversions and slash chords, guitar voicings found and scored for playability, the circle of fifths, common progressions to play along to, and a transposer and capo helper.

Instrument tuner Tune a guitar, bass, ukulele, violin, cello, mandolin or banjo with your phone or computer's microphone — automatic string detection in standard and alternate tunings, a cents needle and a strobe, a steadiness meter, A4 from 415 to 466 Hz, historical temperaments for harpsichord and organ, and reference tones.

MIDI monitor, controller and step sequencer Watch every message on your MIDI ports decoded (notes, controllers, programs, pitch bend, clock and BPM, MTC, SysEx with the maker's name and identity replies), play a keyboard with wheels and assignable sliders, send raw bytes and SysEx files, and program a 16-step drum or melodic sequencer — with a built-in synth when there's no device.

Piano and guitar trainer Learn songs on the piano or guitar: notes fall onto a keyboard with finger numbers and the staff scrolls along, or the song appears as tab, on a fretboard and as chord charts with a strumming pattern. Watch it, let it wait for you, or play along and get scored — with a MIDI keyboard, the computer keys, touch, or the microphone — and import your own MIDI and MusicXML files.

Speaker box designer Design a loudspeaker enclosure from a driver's Thiele/Small parameters — sealed, vented (QB3, B4, BB4, C4 or your own tuning) or 4th-order band-pass — with SPL, cone excursion against Xmax, group delay, impedance and port air speed plotted, the port length worked out, and the box turned into panel sizes and a cut list.

Synthesizer A polyphonic subtractive synthesizer in the browser — three oscillators with pulse-width modulation, noise and unison, a resonant 12 or 24 dB filter with its own envelope, two LFOs, glide and mono legato, distortion, chorus, delay and reverb, an arpeggiator, 26 original presets, and an "explain" mode that says what each section does. Play it on screen, from the computer keyboard or a MIDI keyboard.

Aviation

9 Air routes and great circles · Aviation weather: METAR and TAF decoder · E6B pilot calculators · Flight tracker …

Air routes and great circles Great-circle distance, initial and final course, and midpoint between airports; multi-leg routes drawn on a map across the date line; a flight-time estimate by aircraft type; a per-passenger CO₂ estimate; and an airport lookup with runways and elevation.

Aviation weather: METAR and TAF decoder Fetch METARs and TAFs by station or for airports near you, or paste them, and read them in plain English — wind and gusts, visibility, RVR, weather, cloud and ceiling, temperature, altimeter, remarks, and TAF FM/BECMG/TEMPO/PROB groups on a timeline — with VFR/MVFR/IFR/LIFR colours, runway crosswind, and density altitude.

E6B pilot calculators The flight computer on your phone: wind triangle and wind finding, runway crosswind, pressure and density altitude, true airspeed and Mach, time/speed/distance and fuel with reserves, climb and descent planning, weight and balance with a CG envelope chart, glide range, and unit conversions. Not for navigation.

Flight tracker Live aircraft near you or any airport — on a map or an offline radar scope, in a sortable table, and as an "overhead now" list — from public ADS-B feeds or your own receiver's aircraft.json, with trails, altitude colours, emergency-squawk alerts and a watchlist.

Jet engines and gas turbines How jet engines work and what their numbers mean: an animated cutaway of turbojet, turbofan, turboprop, turboshaft, ramjet and afterburning engines with numbered stations; ideal and real Brayton cycle analysis at any Mach and altitude — thrust, TSFC, efficiencies, T–s and P–v diagrams and trade studies; compressor stages, draggable velocity triangles and a compressor map with surge margin; approximate figures for real engine families; and fuel, run time and start-up for model turbojets.

Mode S and ADS-B decoder Decode 1090 MHz Mode S and ADS-B messages field by field — CRC and parity, callsign, altitude, CPR positions with the maths shown, velocity, Gillham codes and Comm-B — from pasted hex, AVR or Beast frames, or live from your receiver over a WebSocket.

Nav log and VFR planner Plan a VFR cross-country: waypoints from airport codes, coordinates or a tap on the map; great-circle course and distance; magnetic variation from the World Magnetic Model; winds aloft per leg (typed or the US forecast from aviationweather.gov); wind correction angle, true and magnetic heading, ground speed, time and fuel per leg with climb, descent, taxi and reserve; checkpoints; and a printable kneeboard nav log.

Plane spotter "What's that plane?" — point your phone at the sky and see the aircraft labelled where they are, with callsign, type, altitude and distance, using your location, the phone's compass and tilt, and optionally the camera; a sky plot and a list work everywhere else.

Weight and balance Weight and balance for your own aircraft: a profile with empty weight and arm, loading stations, fuel tanks and normal/utility CG envelopes, kept in your browser with JSON export; zero-fuel, take-off and landing weight and CG on the envelope with the fuel burn line and every limit checked; lb/in, kg/mm or kg/m; a printable sheet. Examples for the Cessna 172S, Piper Archer III and Cirrus SR22.

Home automation and devices

7 ADB for Android and Fire TV · Energy usage analyser · Floor plan and building layout · Garden planner …

ADB for Android and Fire TV Android Debug Bridge in the browser — over WebUSB or the network (port 5555 through the gitwebsite app): device info, logcat, a shell, APK install, apps, files, screenshots and recordings, and a TV remote for Fire TV and Android TV.

Energy usage analyser Import your smart-meter data (Green Button XML or CSV, Octopus, Home Assistant, or any interval CSV) in the browser; see every hour as a heatmap, daily and monthly use, baseload and peaks; price it on flat, tiered and time-of-use tariffs you can edit; and try an EV, a heat pump, solar and a battery against your own hours.

Floor plan and building layout Draw a building floor by floor — walls with clean joins, doors, windows, stairs, rooms with their areas, dimensions, labels and scale-true furniture — over an imported plan image you calibrate and trace by hand or with automatic wall detection, see it in 3D, and export SVG, PNG, DXF (a layer set per floor) or JSON, or print it to scale.

Garden planner Frost dates (yours, or NOAA normals for a city), a sowing calendar for each crop from an extension-service planting guide — start indoors, transplant, sow, fall sowing, harvest — succession sowings, square-foot beds with plant counts, companion hints labelled evidence or folklore, and a printable plan, kept in your browser.

Heat loss and HVAC sizing A room-by-room heat-loss and cooling-load estimate in the style of Manual J (not Manual J): U- or R-values and areas, air leakage, design temperatures for a few US cities with sources, window solar gain from the sun's position, and heat-pump sizing with the balance point — in imperial or metric.

Smart-home toolkit Home Assistant from the browser (entities and history, a service caller built from each service's schema, a template tester, the event bus), an automation YAML linter and explainer, Shelly, Tasmota and Hue controls, and a Matter setup-code decoder and encoder.

TV remotes: LG webOS, Roku, Samsung A phone-sized remote for LG webOS (SSAP and its pointer socket), Roku (External Control Protocol) and Samsung Tizen TVs on your network — apps, inputs, volume, text entry and toasts — plus developer-mode notes for each.

Oceanography

1 Ocean lab

Ocean lab Predict tides from NOAA harmonic constituents and check them against NOAA's own predictions; solve the wave dispersion relation, grow wind waves, shoal and break them; compute TEOS-10 seawater properties with a T–S diagram and CTD profiles; work out Coriolis, Ekman and geostrophic currents; and plot NDBC buoy observations.

Everyday

11 Bookshelf · Dictation scratchpad (speech to text) · Google Docs connector · Loan and mortgage calculator …

Bookshelf A catalogue of the books you own, made for a phone at the shelf or in a bookshop — scan barcodes (a whole shelf at a time), look books up at Open Library and Google Books, sort them onto rooms, bookcases and shelves, track reading, loans and a wishlist, ask "do I own this?" in a shop, and sync phone and computer by file or through your own GitHub gist.

Dictation scratchpad (speech to text) Dictate into notes kept in your browser. Speech is recognised locally with OpenAI's Whisper running in the page — the audio never leaves your device — or with the browser's own speech recognition, with live words as you speak.

Google Docs connector An experiment in connecting browser tools to Google Docs — sign in with Google, pick or create a document, read it, and append notes from a scratchpad (at the end, under a heading, or into a section a tool keeps up to date). The app can only see documents you pick or create here.

Loan and mortgage calculator Loan and mortgage payments with a full amortisation schedule and chart, extra and lump-sum payments, refinance break-even, affordability by debt-to-income ratio, and APR with fees.

Markdown résumé builder Write your résumé in Markdown, see it typeset live in five themes on A4 or Letter, and print it to PDF or save it as HTML, plain text, Markdown, or JSON Resume.

Recipe scaler Paste any recipe and scale it by servings, a factor, a pan size, or the amount of one ingredient you have; convert between US and metric, cups to grams; and see baker's percentages and dough hydration.

Sewing, knitting and crochet calculator How much fabric — pattern pieces packed on the fabric width (folded or single, nap, seam allowance) — plus quick estimates for skirts, curtains and cushions, bias and binding, knitting and crochet gauge and resizing, CYC yarn weights and yarn quantities, increasing or decreasing evenly across a row, and grading measurements between sizes.

Tab sets Turn the tabs open in Chrome into a shareable link — drag tabs or bookmarks in, paste them, or load Chrome's bookmarks export, no extension needed — then edit titles, notes, a group name and colour, and re-share or open them.

Text to speech Read text or Markdown aloud on your own device — with your system's voices (word-by-word highlighting, rate, pitch, volume) or Kokoro, a neural voice model that runs in the browser — and download the speech as a WAV file.

Timers, Pomodoro and talk timer A talk timer for a list of talking points — each with its own Markdown notes and time, adding up to the length of the talk, run point by point from any starting point — plus a Pomodoro timer with a session log, named countdowns, a stopwatch with laps, and an interval timer for Tabata and HIIT.

Work log and tasks A private work log and task list in your browser — tasks nested as deep as you like with due dates, effort and recurring rules, a timestamped journal, timers and timesheets that roll up by project, and a “what’s on my plate” view — with quick-add typing, undo, and JSON, Markdown and CSV import and export.

Games

10 Boing pinball · Box Rally · Brick tunnel · Cube Serpent …

Boing pinball A 3-D pinball table of my own, Comet Tour, played with a red-and-white chequered Boing ball — flippers, slingshots, pop bumpers, drop targets, a spinner, a ramp, a skill shot, multiball, five missions and a dot-matrix display — on keyboard, touch or gamepad.

Box Rally A 3D paddle game down a glowing box, seen from behind your paddle: move as you hit to put spin on the ball and bend its path, play the computer at four levels or a friend on a split screen, with curve, split and shrink power-ups. First to 11.

Brick tunnel A brick-breaker down a 3-D tube — your paddle runs round the rim, the chequered ball rides the wall and bounces off the far end, and the bricks sit on rings receding into the depth — with multi-hit, metal and explosive bricks, spinning rings, five power-ups, boss rings, ten built-in levels and seeded generated ones.

Cube Serpent A snake game on the six faces of a cube: run over the edges, eat gems, use portals, dodge walls — or ride light cycles against one to three AI rivals. Keyboard, touch and gamepad.

Lander 3D Land on the Moon, on windy Mars and on a small asteroid — generated terrain with craters, three pads worth ×1, ×2 and ×5, a main engine and RCS thrusters for pitch and roll, limited fuel, a touchdown check on speed and attitude, and a replay of every landing.

Marble tilt Roll a steel marble through a maze on a tilting 3D board — holes, railed and narrow bridges, moving platforms, bumpers and checkpoints — by tilting your phone, dragging, or with keys or a gamepad. Twelve designed levels, endless levels from a seed, and best times.

Mine Sphere Minesweeper on a globe of hexagons and twelve pentagons — five sizes, three densities, chording, a first click that is always safe, and an optional no-guess board that a built-in solver proves can be cleared by logic.

Neon Runway An endless 3D runner on a neon road above a grid: three lanes, curves, hills and gaps, walls to dodge, bars and gaps to jump, orbs and boost pads, a synth soundtrack written as you drive — and a table of your best distances.

Stack tower A falling-block puzzle on the outside of a round tower: 16 columns that wrap all the way round, an original set of three- and five-square pieces, hold, ghost, ring clears, and three modes — Marathon, Rising rubble and a Dig challenge.

Vector Drift A wireframe rock-field shooter in a cube of space that wraps on every side — a drifting ship with thrust and a risky hyperspace jump, rocks that split, two kinds of saucer — and between waves the debris you missed falls on the cities below, to be stopped with interceptors.

Retro computing

60 6502 assembler · 68000 assembler and disassembler · 68000 cycle counter · 8086 assembly playground …

6502 assembler Assemble and disassemble 6502 and 65C02 code in the browser, with labels, local labels, expressions, and an optional undocumented-opcode set; download raw binaries, Atari binary-load files, or C64 PRGs; search the full opcode table with cycles and flags.

68000 assembler and disassembler Assemble Motorola 68000 code in the browser and export S-records (S19/S28/S37), Intel HEX, raw binary, a C array, an Amiga hunk executable or an Atari ST .PRG; disassemble hex, binaries, S-records or Intel HEX with a byte-exact reassembly check; inspect and convert S-record files.

68000 cycle counter Paste 68000 assembly and see the clock cycles and bus reads/writes of every instruction from Motorola's timing tables, the total for a block or loop, and how much of an Amiga or Atari ST frame it takes.

8086 assembly playground Write 8086 assembly in NASM syntax and step through it as a DOS .COM program: every instruction's bytes split into prefix, opcode, ModR/M, displacement and immediate with each field explained, registers and flags with changes highlighted, segment:offset addresses with the 20-bit physical address, Intel's clock count for every instruction (8086 or 8088), an 80 × 25 colour text screen at B800:0000, BIOS and DOS interrupts, and the keyboard.

A chess program for the Z80 A small chess program I wrote in Z80 assembly, playing on an emulated ZX Spectrum 48K at 3.5 MHz — 0x88 board, legal moves with castling, en passant and promotion, alpha-beta search with quiescence. Watch the Z80 think (nodes, emulated time, the line it's searching, a routine profile, a debugger), check its move generator with perft, and download a .TAP for a real Spectrum.

Acorn Electron: emulator, BBC BASIC, assembler and debugger An Acorn Electron in your browser — the Electron ULA with MODEs 0–6, its palette registers and the RAM contention that slows the CPU in MODEs 0–3, the single sound channel, the keyboard matrix and UEF tapes through the ULA's cassette interface — with your own Acorn ROMs or an open stand-in OS. Type BBC BASIC, write 6502 assembly and debug it with breakpoints beside the code.

Amiga ADF disk images Explore Amiga .adf and .adz floppy images in the browser — bootblock, root block, block map, directory tree with dates, protection bits and comments — extract files or the whole disk as a ZIP, verify checksums, and create new OFS or FFS disks with your own files.

Amiga archives: LHA, LZX, DMS and Zip Open Amiga archives in the browser — LHA/LZH (-lh0- to -lh7-), LZX, DMS disk images (every packing mode, including obfuscated ones) and Zip — list them with sizes, dates, protection bits and comments, check CRCs, extract files or everything as a ZIP, and send a DMS disk or an ADF inside an archive to the ADF explorer.

Amiga blitter lab Work out Amiga blitter set-ups: minterms from a truth table, Venn diagram or Boolean expression (and LF back to the shortest expression), cookie-cut, masked, XOR, clear, rectangle and area-fill blits stepped word by word with shifts, masks and modulos, line mode with octants and the Bresenham registers, the DMA cost, and the register set-up as C or assembler.

Amiga custom chip registers Every OCS, ECS and AGA custom chip register at $DFF000, searchable; bit-field decoders for DMACON, INTENA, BPLCON0–4, ADKCON, POTGO and more; a display-window and data-fetch calculator; a blitter minterm calculator; and a copper list assembler and disassembler.

Amiga dev bench Write 68000 assembly, build it with the real vasm assembler and vlink linker compiled to WebAssembly, and boot it on an emulated Amiga 500 (vAmiga) with the free AROS Kickstart, or your own ROM. Includes examples, a listing, a hunk view, downloadable ADFs, and the vAmiga debugger.

Amiga DMA slot timing See who owns every colour clock of an Amiga scanline — refresh, disk, audio, sprites, bitplanes, copper, blitter and the 68000 — and how screen depth, resolution, overscan and blitter-nasty steal chip-RAM time, with per-frame and per-second budgets for PAL and NTSC.

Amiga emulator An Amiga in your browser — vAmiga compiled to WebAssembly, booting the free AROS Kickstart or your own ROM. Boot your own ADF disks on an A500 or an A1200.

Amiga hunk executables and 68000 disassembler Inspect Amiga executables — hunk header, CODE/DATA/BSS hunks with CHIP and FAST flags, relocations, symbols, LINE debug info, and overlays — disassemble 68000 code with labels, turn hex into 68000 instructions, and look up any 68000 instruction's flags and cycle timings.

Amiga library reference Every AmigaOS library, device, resource and BOOPSI class function from the 3.2 NDK — its LVO, registers, C prototype, and the Kickstart version that added it — with a decoder that names the jsr -nnn(a6) calls in a disassembly and generators for LVO includes, FD files and SAS/C pragmas.

Amiga sprites and BOBs Draw Amiga hardware sprites (3 colours, or 15 as an attached pair) and blitter objects of any depth, animate them frame by frame, import a PNG onto the palette, and export the data words with SPRxPOS/SPRxCTL, or the BOB's planes, mask and cookie-cut blitter set-up, as assembler or C.

AmigaGuide viewer Read Amiga .guide hypertext in the browser — nodes, links, bold, italic and pens, @wordwrap and @smartwrap, macros — with the Contents, Index, Help, Retrace and Browse buttons, straight from a file, an ADF disk image, or an LHA, LZX, DMS or Zip archive.

Amstrad CPC emulator and Z80 IDE An Amstrad CPC 464 and 6128 in your browser with the original firmware and Locomotive BASIC, a Z80 assembler and debugger with the firmware's jumpblock names, live views of the Gate Array, CRTC, PPI, AY and floppy controller, and DSK, CDT and SNA support.

Apple II: emulator, assembler and debugger An Apple II+ or IIe in your browser — text, lo-res and hi-res with NTSC artifact colour or a monochrome monitor, the speaker, and a Disk II that reads .DSK, .DO, .PO, .2MG and .NIB images as real GCR nibbles. Write 6502 assembly and debug it with breakpoints beside the code, stepping, registers, memory and the soft switches. Load your own ROMs; without them a stub monitor written for this site runs.

Atari 2600 IDE Write Atari 2600 (VCS) programs in 6502 assembly — DASM-style, with vcs.h and macro.h built in — assemble them to a 2K, 4K or 8K cartridge, and run them in an emulator with a debugger: step by instruction, scanline or frame, breakpoints, registers, RAM, TIA state, the beam position, and a frame-timing check.

Atari 8-bit computer: emulator, BASIC, assembler and debugger An Atari 800, 800XL or 130XE in your browser (atari800 in WebAssembly, the free Altirra OS and BASIC) — run disks, programs, cartridges and tapes; type and save BASIC; write 6502 assembly and run it, or call it from BASIC with USR; and debug anything that runs with breakpoints, stepping, registers, memory, the ANTIC/GTIA/POKEY/PIA registers and the display list.

Atari 8-bit disk images Open ATR and XFD disk images from the Atari 400/800/XL/XE — header, VTOC map, Atari DOS 2.0/2.5 and MyDOS directories, sector chains, binary-load segments, ATASCII text, and a sector hex viewer.

Atari BASIC lister List tokenised Atari BASIC programs as text, convert ATASCII to and from text, compose 40×24 text screens and export them as bytes, and pick colours from the GTIA palette with ready-to-type POKE values.

Atari ST disk images Open .ST and .MSA floppy images in the browser — boot sector and BPB, FAT12 cluster map, folders, PRG headers — extract files, convert between ST and MSA, create blank disks, and add files.

Atari ST emulator An Atari ST or STE in your browser — Hatari compiled to WebAssembly, booting the free EmuTOS. Put disk images in A: and B:, programs on an emulated hard disk C:, autostart a program, play with keys or a gamepad, save states, and convert MSA ⇄ ST images.

Atari ST pictures View and convert Degas (PI1–3, PC1–3), NEOchrome (NEO), and Spectrum 512 (SPU) pictures with ST and STE palettes and colour-cycling info; export PNG, or convert any image back to PI1, PC1, or NEO.

BBC Micro: emulator, BBC BASIC, assembler and debugger A BBC Micro Model B in your browser — 6845 CRTC and video ULA (MODEs 0–7 with MODE 7 teletext), both 6522 VIAs, the SN76489, UEF tapes and SSD/DSD discs through an emulated 8271 — with your own Acorn ROMs or an open stand-in OS. Type BBC BASIC (inline [ ] assembler included), write 6502 assembly, and debug with breakpoints beside the code, stepping, OS call labels and chip views.

C64 BASIC and PETSCII Commodore 64 BASIC V2 tokeniser and detokeniser (PRG ↔ listing with {clr}/{red} control codes), PETSCII ↔ Unicode for both character sets, and a 40×25 PETSCII screen editor that exports screen and colour bytes, a BASIC PRINT program, or 6502 assembler.

C64 disk images (D64) Open Commodore 1541 .D64 images — BAM, disk name and ID, the directory as the C64 lists it, file types, track/sector chains, a block map, a sector hex viewer, PRG load addresses, file and ZIP extraction — and build new disks with your own files.

CHIP-8 IDE and emulator Write, assemble, run and debug CHIP-8, SUPER-CHIP 1.1 and XO-CHIP programs in an Octo-style assembly language — an interpreter with the well-known quirks as switches, 60 Hz timers, sound and XO-CHIP's audio patterns, a keypad, breakpoints, registers, memory and a disassembler, with eight example programs. Load your own .ch8 files.

Commodore 64: emulator, BASIC, assembler and debugger A Commodore 64 in your browser — the cycle-stepped chips emulator in WebAssembly, booting the free MEGA65 Open ROMs (or your own). Run PRG, D64, T64 and TAP files; type and save BASIC; write 6502 assembly and run it, or call it from BASIC with SYS; and debug anything that runs with breakpoints beside the code, stepping, registers, memory, and the VIC-II, SID and CIA registers.

Commodore PET: emulator, BASIC, assembler and debugger A Commodore PET in your browser — the 2001, 3032 and 4032 with the 40-column screen, or the 80-column CBM 8032; graphics or business keyboard, green, white or amber phosphor, the CB2 beeper, the 6520 PIAs and the 6522 VIA. It boots Microsoft's open-source BASIC 1.1 on a KERNAL written for this site, or your own ROMs; loads PRG, D64 disks and TAP tapes, and saves to them. Write 6502 assembly and debug it beside the code.

Commodore VIC-20 and PET: emulator, assembler and debugger A Commodore VIC-20 (PAL or NTSC, with memory expansions and cartridges) or PET 2001 / 3032 / 4032 / 8032 on one page — the VIC chip's video and sound, the 6522 VIAs and 6520 PIAs, the keyboards, PRG, D64 and TAP files. Boots Microsoft's open-source BASIC 1.1 on a KERNAL written for this site, or your own ROMs. Write 6502 assembly and debug it with breakpoints beside the code.

Commodore VIC-20: emulator, BASIC, assembler and debugger A Commodore VIC-20 in your browser — PAL or NTSC, unexpanded or with 3 to 35 KB of expansion, the VIC chip's 22 × 23 screen, colours, multicolour and custom characters, its three voices and noise, both 6522 VIAs, keyboard and joystick (gamepad too). It boots Microsoft's open-source BASIC 1.1 on a KERNAL written for this site, or your own ROMs; loads PRG, D64 disks, TAP tapes and cartridges, and saves to disk and tape. Write 6502 assembly and debug it beside the code.

Copper and blitter playground Write an Amiga copper list and watch it run against the PAL or NTSC beam — raster bars, split palettes, per-pixel colour changes, animated with expressions — and run real blits with shifts, masks, minterms, and area fill on bitmaps you draw.

Copper gradients and raster bars Design colour gradients and shaded raster bars, see them quantised to Amiga OCS/ECS, AGA, Atari ST or STE colour depth with optional dithering, and export a copper list with the line-255 wrap handled, a UCopList in C, an HBL colour table, a palette ramp, or a sine table.

Dragon 32/64 and TRS-80 Color Computer: emulator, 6809 assembler and debugger A Dragon 32, Dragon 64 or TRS-80 Color Computer 2 in your browser — a cycle-counted Motorola 6809, the SAM 6883, the MC6847 VDG with every text, semigraphics and graphics mode (and NTSC artifact colours), both 6821 PIAs, the 6-bit DAC, joysticks, CAS tapes, cartridges — with your own BASIC ROMs or an open 6809 monitor. Write 6809 assembly and debug it with breakpoints beside the code.

FS-UAE and WinUAE configuration builder Build FS-UAE and WinUAE / Amiberry configurations for any Amiga from the A1000 to the CD32 — CPU, chipset, memory, Kickstart, floppies, hard drives, RTG and input — with checks for combinations that will not boot, and identify Kickstart ROM files by CRC and header.

Gamepad and joystick tester Test a game controller in the browser — every button and axis live, stick drift and a suggested dead zone, a circularity score, trigger range, button chatter, polling rate and rumble — and build an SDL GameControllerDB mapping for pads the browser doesn't know.

IFF ILBM pictures and 8SVX sounds View Amiga IFF pictures — ILBM with HAM6, HAM8, EHB, hires and interlace, masks and pixel aspect — play 8SVX samples, browse the chunk tree of any IFF file, export PNG, and convert your own images to ILBM.

Jupiter Ace emulator and Forth workbench The Jupiter Ace — the 1982 home computer that booted into Forth — in your browser on its own ROM: type Forth through its line editor, watch the dictionary grow, call Z80 code from Forth with a debugger, and load and save .TAP tapes and .ACE snapshots.

Kickstart and TOS ROM identifier Identify an Amiga Kickstart or Atari TOS ROM image — version, model, header fields, checksum (and fix it), CRC32, SHA-1 and MD5 — merge split hi/lo EPROM dumps, undo byte swapping, and decrypt Amiga Forever ROMs with their rom.key. Nothing is uploaded.

Memotech MTX emulator and Z80 IDE A Memotech MTX500, MTX512 or RS128 in your browser — Z80 at 4 MHz, the TMS9929A video chip, the SN76489 sound chip, the Z80 CTC's interrupts, the IOBYTE memory paging, the keyboard matrix and .MTX tapes — running your own Memotech ROMs for MTX BASIC, or an open stand-in monitor, with a Z80 assembler, examples and a debugger with breakpoints beside the code.

MSX emulator and Z80 IDE An MSX1 in your browser — TMS9918A video (every mode, sprites, fifth-sprite and collision flags), AY-3-8910 sound, slots, mapper cartridges with Konami SCC, and .CAS tapes — booting the open-source C-BIOS (or your own MSX BIOS for BASIC), with a Z80 assembler, MSX examples and a debugger with breakpoints beside the code, VDP, PSG and slot views.

Oric-1 and Atmos: emulator, assembler and debugger An Oric Atmos or Oric-1 (16K or 48K) in your browser — the ULA's 40×28 text and 240×200 HIRES with serial attributes, the 6522 VIA, the AY-3-8912, the keyboard matrix, and .TAP tapes loaded and saved at once through ROM traps. Write 6502 assembly and debug it with breakpoints, stepping, registers, memory and chip views. Load your own BASIC ROM; without it a stub monitor written for this site runs.

Paula audio, MOD tracker and player Compose ProTracker MOD music in the browser — pattern editor with the ProTracker keyboard, on-screen piano and MIDI, sample editor with WAV/8SVX import, recording and chip waveforms — plus Paula period/note/rate conversion, Paula periods and sample rates on PAL or NTSC, see the complete ProTracker period table with finetunes and DMA timing, and inspect and play MOD files.

POKEY sound designer Design Atari 400/800/XL/XE POKEY sounds — four channels of AUDF/AUDC with every distortion mode and volume-only output, AUDCTL 16-bit linking, 1.79 MHz clocking, high-pass filters and 9-bit poly — hear them through a POKEY model, and export Atari BASIC SOUND, POKEs, assembler or PAL/NTSC note tables.

ProTracker MOD player and editor Play and edit Amiga ProTracker MOD files with a replayer that follows ProTracker 2.3D tick by tick — every effect and E-command, the period table with finetunes, PAL/NTSC clocks, the A500/A1200 output and LED filters, stereo separation — with a scrolling pattern view, per-channel scopes, mute and solo, keyboard pattern editing, a sample editor with WAV import, and .MOD and WAV export.

Retro bitmap font editor Draw and edit 8-pixel-wide bitmap fonts for the Amiga, C64, Atari 8-bit and ST, or any microcontroller — transform glyphs, preview text on classic screens, rearrange into C64 screen-code or Atari order, and export raw ROM images, .64c, .fnt, PSF, PNG sheets, C or assembler tables, or an Amiga TextFont.

Retro disk and tape images One toolkit for retro disk and tape images — Amiga ADF, C64 D64/D71/D81/T64/TAP, Atari ATR and ST/MSA, Amstrad CPC and Spectrum +3 DSK, ZX TAP/TZX, BBC SSD/DSD, Apple II DOS 3.3 and ProDOS, MSX and PC FAT — auto-detected; browse, view files as hex, text in the machine's own character set, listed BASIC or pictures; add, delete and rename; create blank disks, convert, and open them in the emulators.

Retro image converter Convert a modern picture for an Amiga (OCS/ECS, EHB, HAM6, HAM8, AGA, sliced palettes with a copper list), Atari ST (incl. Spectrum 512), C64 (hires, Koala, FLI), ZX Spectrum, NES, Game Boy, CGA/EGA/VGA, Atari 8-bit or MSX — with the machine's real constraints, a live before/after view, dithering, and native files to download.

Retro raster timing PAL and NTSC raster maths for the Amiga, Atari ST, Atari 8-bit, and C64 — cycles per line and frame, frame rates, µs per scanline, unit conversions, a per-frame cycle budget, and the cycles DMA steals.

SAM Coupé emulator and Z80 IDE A SAM Coupé in your browser — the 6 MHz Z80 with memory contention, all four screen modes, the 128-colour palette, line interrupts, LMPR/HMPR/VMPR paging, SAA1099 stereo sound, the keyboard and mouse, and MGT/SAD/DSK disks through a VL1772 — booting SAM ROM 3.0 to SAM BASIC, with a Z80 assembler, examples (mode 4 palette cycling, raster bars, SAA1099 music) and a debugger.

SID sound designer Design Commodore 64 SID sounds — three voices with triangle, saw, pulse and noise (and combinations), real ADSR rates, ring modulation, hard sync, the 6581/8580 filter — play them from the keyboard, and export the $D400–$D418 registers as BASIC POKEs, assembler, or PAL/NTSC note tables.

Sinclair QL emulator A Sinclair QL in your browser — a 68008 at 7.5 MHz, the ZX8301 and ZX8302, the IPC's keyboard and BEEP sound, and two microdrives — booting the open-source Minerva ROM into SuperBASIC. Type in or paste listings, read and write .mdv cartridge images, and assemble 68000 code with a debugger.

TRS-80 emulator and Z80 IDE A TRS-80 Model I or Model III in your browser — the 64 × 16 screen with its 2 × 3 block graphics, the memory-mapped keyboard, the clock interrupt, cassette sound, .CAS tapes and .CMD programs — booting GW-80, an open monitor ROM written for this page (or your own Level II ROM for BASIC), with a Z80 assembler, examples and a debugger.

Workbench icon editor (.info) Open, draw and save Amiga Workbench icons — classic planar .info images in the 1.3 or 2.0+ colours, NewIcons hidden in the tooltypes, and OS 3.5 ColorIcons — with the icon type, default tool, tooltypes, stack and drawer window, PNG import and a byte-level file layout.

YM2149 / AY sound designer Design sounds for the Yamaha YM2149 and AY-3-8910 (Atari ST, ZX Spectrum 128, Amstrad CPC, MSX) — three tones, noise, all 16 envelope shapes, the mixer, live registers and code export — and play or inspect .YM music files (LHA-packed YM3/YM5/YM6) and SNDH headers.

ZX Spectrum emulator and Z80 IDE A ZX Spectrum 48K and 128K and a Timex Sinclair TS2068 / TC2068 in your browser, with the original ROMs, a Z80 assembler and a debugger — assemble and run example programs (including Timex hi-res and hi-colour), set breakpoints, step through code, and inspect registers, memory, bank maps and screen addresses. Loads TAP, TZX, SNA, Z80 and DCK files.

ZX81 emulator and Z80 IDE A Sinclair ZX81 (1K or 16K) in your browser running the original ROM, with a Z80 assembler that builds REM-statement programs, a debugger with breakpoints and single-stepping, and .P file loading and saving.