Build an atom by adding and removing protons, neutrons and electrons, and watch how they arrange themselves: a periodic table of all 118 elements, ions and isotopes, electron configuration with its 20 real exceptions, and a folding view that goes from the orbital to the valence band.

Independent dice tables with numeric and symbolic dice. Roll all at once or per table.

Compares two texts line by line and shows differences with colour highlighting (added/removed).

Generate fake data for testing: names, emails, phones, IPs, UUIDs, dates, IBAN and more.

Markdown editor with real-time preview in split or preview-only mode.

Simulate the monthly cost of using different AI models based on your request volume and prompt size.

Build a quantum circuit with qubits and gates (H, X, Y, Z, CNOT, Toffoli...) and watch superposition, entanglement, the Bloch spheres and measurement live. Bell, GHZ and Grover demos.

Simulate your Makefile in the browser: build a pretend project with its timestamps, touch a file and see exactly what make would rebuild, in what order and WHY — with the recipe already expanded. It warns about what actually bites: the tab character, the cd that does not survive into the next line, the dollar sign make eats, and the missing dependency that only blows up under -j. It runs nothing.

Test regular expressions in real time and visualize all matches with their position.

Convert between JSON, YAML, Properties, ENV and CSV with automatic input format detection.

Calculate the contrast ratio between two colours and verify WCAG 2.1 AA and AAA compliance for normal and large text.

Visualize and edit Basic, Bearer/JWT and OAuth2 (Authorization Code and PKCE) as step-by-step sequence diagrams. Here you see the protocol/flow; the JWT is one step — to inspect the token in detail see the JWT inspector.

Write SQL against a real Postgres in the browser: schema-aware autocomplete, live validation, warnings and optimization suggestions (indexes, SARGability). No server.

A simulated file explorer that, instead of moving files, shows you the command that would do it: double-click a folder and the «cd» appears, right-click to copy, rename or delete, and the script builds up below ready to copy. The same gesture in Linux, macOS, PowerShell and CMD, with names properly quoted and real errors. It runs nothing and never touches your disk.

Convert colors between HEX, RGB and HSL with live preview.

Apply filters (kernels) to an image and see the resulting feature map: edges (Sobel), blur, sharpen, emboss… the basic operation of a convolutional network (CNN). Edit your own kernel, upload an image and watch the "filter bank" that mimics a CNN's first layer.

Visualize CSV data as line, bar, area, pie, or scatter charts. Export as PNG.

Encodes with parity bits and corrects 1-bit errors; includes SECDED (detects 2), interactive error injection, parity coverage and a noisy-channel simulator.

Paste one or more skaffold.yaml and see the dependency graph (requires). It validates cross-references: a requires pointing to a misspelled config name shows in red. Rename a config and its requires update. No server.

Merge PDFs, extract pages, add watermarks and view document metadata.

Calculate capital growth with monthly contributions and annual compound interest.

Write a list of options and pick one at random with animation. Saves result history.

See how models learn: a ball rolls down a loss surface with SGD, Momentum, RMSProp or Adam. Change the learning rate and momentum and watch the animated trajectory; try local minima and Rosenbrock.

Extract the text from an image (photo, screenshot, scan) right in your browser, without uploading anything to any server. Upload, drag or paste the image and get the text with each word's box colored by its confidence. Pick the language, fix the uncertain words and copy or download it. Tesseract engine downloaded from the CDN and cached (offline afterwards).

Generate the Nginx config or Apache .htaccess to correctly serve a Single Page Application with client-side routing.

Simulate rate limiting algorithms (Token Bucket and Fixed Window) with a visual timeline of accepted and rejected requests.

Transform text between camelCase, snake_case, PascalCase, kebab-case and more.

Look up full information for any character: codepoint, UTF-8/16, HTML entity and ASCII table.

Configurable Pomodoro timer with session counter and work, short break and long break phases.

Ohm's law, series and parallel resistors, and resistor color code decoder.

Turn on your camera and detect objects live with a 10 MB model running in your browser: it warns you when something appears —or when it STOPS being there—, counts appearances and gives you the log as CSV. You can have several rules at once, each with its own object, threshold and zone drawn over the image, all watching the same video. Neither the video nor the detections leave your device, and there is a network-request counter in plain sight so you can check it.

Paste a log or open a file and actually understand it: it groups exception stack traces as ONE event (not forty lines), mines the patterns that repeat, points at the root cause, reviews your logging hygiene, and shrinks it to a token budget you can paste into an AI. Java, Python, Node, Go, .NET, JSON, logfmt and syslog. 100% in your browser.

Build URLs with UTM parameters for marketing campaigns or decode an existing URL to extract its parameters. Specialized in campaigns (utm_*); to break down any URL see URL Parser.

Calculate BMI, ideal weight, basal metabolic rate (Harris-Benedict) and recommended bedtimes.

Evaluates advanced mathematical expressions and shows the result as rendered LaTeX.

chmod (octal/symbolic permissions with special bits), chown and a users & groups command builder (useradd, usermod, groupadd) with warnings and a per-flag explanation.

Convert a docker run command with its flags to an equivalent docker-compose.yml file.

A real Postgres database in your browser: write SQL, see tables and relationships as a diagram, and query sample data. No server.

Calculate the real cost of a meeting (one-off and annual if recurring) based on attendees, hourly rate and duration.

Project high-dimensional data (or embeddings) to 2D with PCA, t-SNE and UMAP, and watch them organize live. Compare the linear method (PCA) with the non-linear ones, try the swiss roll and tune perplexity/neighbors. It teaches the algorithms with generic data; to project real sentences see the Semantic map.

Statistics calculator (descriptives, charts), interactive distributions and probability simulators to understand data and uncertainty.

Generate SHA-256, SHA-384 and SHA-512 hashes directly in the browser using Web Crypto API.

Generate and validate cron expressions with a visual builder, text humanisation and next execution times.

Analyse and explain in plain language the CORS headers your server sends. Shows what is missing to allow a cross-origin request.

Diagram software/hardware architectures (CI/CD, cloud, AI/MCP agents, data flows) with typed components and simulate load in real time: queues, latency, throughput and bottlenecks. No server.

Drag points and see the least-squares fit live. Raise the polynomial degree to watch overfitting and use regularization (ridge = MAP with a Gaussian prior) to control it. MSE = maximum likelihood with Gaussian noise.

Converts between bits, bytes and their multiples according to SI (kilo/mega) and IEC (kibi/mebi) standards.

See the diffusion process behind generative AIs like Stable Diffusion: a structured point cloud dissolves into Gaussian noise step by step, and the reverse process rebuilds it.

Calculate days between dates, exact age in years/months/days, day of the week and date operations.

Walk a Markov chain and watch the visit distribution converge to the stationary one; or train a Markov text generator. The basis of MDP, PageRank, MCMC and classic text generation. It teaches chain theory; to train a language model with your text see Mini-LLM.

Generate secure passwords with configurable options and cryptographically secure UUIDs v4.

Prepare the work for an AI and check what it hands back. Write the spec (what changes and, above all, what does NOT) and review it against the rules that make it satisfiable; split permissions into three buckets; export to SPEC.md, Kiro or CLAUDE.md. And from the other side: measure the loop trace, separate what is backed by a source from what is merely asserted (an arXiv paper is a preprint, not a peer-reviewed article) and build an eval bank that reviews itself before giving you any percentage. Includes the system prompt builder.

Calculate the fixed monthly payment (French amortization) and generate the full amortization schedule.

Escape and unescape text to embed it in SOURCE CODE: JavaScript, JSON, SQL, Regex, HTML, URL and CSS. To encode for transport (Base64/URL/HTML) see Encoder/Decoder.

Decode, verify and sign JWT tokens (header, payload, expiration, algorithms). It is the token inspector; to see the full authentication flow (OAuth2/Bearer) see Auth flows.

Open and explore CSV, logs or JSONL of tens or hundreds of GB without loading them into memory: virtual scroll, go to line, "tail" and streaming text/regex search. 100% local.

Turn audio into text with Whisper running in your browser: open a file or record from the microphone and get the transcript with timestamps, ready to export as TXT, SRT, VTT or CSV. Your audio is never uploaded anywhere, and there is a network-request counter in plain sight so you can check it. It also brings the metric a transcript is really judged by — the word error rate — so you can measure it on your own audio and compare two models word by word.

Scoreboard for matches with multiple players, customizable scoring and integrated timer.

See the attention mechanism inside transformers (BERT, GPT): type a sentence and watch which words each token "looks at", with the token-to-token attention matrix, multiple heads and the causal mask of generative models. Interactive: click a word to see its attention arcs.

Chat with LLMs, summarization, translation and sentiment analysis running 100% on your device. No server, no data sent. Powered by Transformers.js.

Create diagrams (flowchart, sequence, ER, Gantt) by writing Mermaid code with real-time preview.

Transform data by chaining nodes: filter, derive columns, clean text and select — all in one pass, 100% in your browser. Per-node preview and output to CSV or the Viewer.

Visual Visio-style diagram editor: drag shapes, connect and edit them. Import and export Mermaid.

Preview LaTeX mathematical formulas in real time with example snippets.

Draw the plan of whatever you run — a bar’s tables, a data centre’s racks, a ward’s beds, an office’s desks, workshop bays, classrooms or campsite pitches — assign who takes what, and see whether it holds up. The part no tool in the sector has: as well as colouring the state, it uses queueing theory to work out how long people wait, how many leave without a spot, and how many resources you would actually need. No account, no server.

Encode or decode text for TRANSPORT: URL, Base64 and HTML entities. To escape text inside source code (JS, JSON, SQL, Regex, CSS…) see String escaping.

The physical design of a chip, from the inside, in five steps that link together: the memory cell and its noise margin (the butterfly curve), how that cell is READ without destroying it, how the current reaches it and how much voltage is lost on the way, what shape it takes on silicon and why height is measured in tracks, and how fast all of that can run. It shows why reading a cell can erase it, why a hold violation is not fixed by lowering the frequency, and how IR drop ends up being paid for in the clock. First-order models, and every screen says so.

Agent-based market simulation: firms competing (Cournot), monopolies, mergers, limited resources and government policy, with a timeline. Understand why prices move (e.g. why RAM gets pricier as HBM is prioritised for AI). No server.

Break a URL into its parts (protocol, host, path, query params) and build new ones.

Simulates a simplified MIPS ISA in the browser. Editor with active-line highlighting, registers, memory, stack and console. Step-by-step or automatic execution with adjustable speed.

Resize images, convert between formats (PNG/JPEG/WebP) and get the Base64 encoding.

Evaluate a binary classifier visually and interactively: move the threshold and watch the confusion matrix, precision, recall, F1, the ROC curve (with AUC) and the precision-recall curve (with AP). Adjust the model's quality and class imbalance to understand how some metrics lie and others don't.

Formula-driven physics in 3D: simple and double pendulum with real units, step-by-step or real-time, selectable integrators (Euler, Verlet, RK4) and energy and phase-space plots.

Converts between bases (2–64) and adds a programmer's calculator (arithmetic and bitwise, two's complement), bit inspector, IEEE 754 and codes (ASCII, Gray, endianness).

Calculate how many months of cash your company has left with optimistic, current and pessimistic scenarios.

Check which package versions satisfy a semantic version range (^, ~, >=, -) and view the syntax cheatsheet.

Visualize how LLMs split text into tokens, compare costs across models (GPT-4, Claude, Gemini, Llama) and estimate how much of the context window your text consumes.

Calculate network, broadcast, host range, mask and usable hosts from CIDR notation.

Calculate how inflation erodes money's value year by year with a global or per-year custom rate.

Calculate the break-even point: how many units you need to sell to cover fixed and variable costs, and the estimated time to reach it.

Visual digital circuit simulator with AND, OR, NOT, NAND, NOR, XOR and XNOR gates. Connect nodes, toggle inputs and watch signal propagation in real time.

Import RDF data (Turtle, JSON-LD, N-Triples, RDF/XML), see it as an interactive graph and query it with SPARQL 1.1 — a whole semantic store in your browser (Oxigraph WASM), no server.

Format, minify and validate JSON with error highlighting and key counter.

Convert a Unix timestamp (s/ms/µs/ns) or any date to every format (ISO, RFC, syslog, Excel, FILETIME…), with time zones, DST and local-vs-UTC detection.

Calculate the statistical significance of an A/B experiment using a two-proportion Z-test. Shows the winner and required sample size.

Train a decision tree (CART) on 2D data and see how it classifies with yes/no questions: the "staircase" decision regions and the tree drawn node by node. Adjust the depth and watch overfitting; choose Gini or entropy. The interpretable model behind random forests and XGBoost.

Train a real neural network in your browser and watch it learn: pick data (circle, XOR, gaussians, spiral) and an architecture, hit play and see the decision boundary form and the loss drop. Click to have it classify a new point. No server, no downloads.

Visually understand p-values, the rejection region and the α level; run t-test, χ², ANOVA and analyze power (type I/II error). To validate whether a model improvement is real or just noise.

Visual statistics playground for AI: interactive distributions (normal, binomial, Poisson…), softmax and temperature, Bayes and entropy. Tweak parameters and watch the curves, samples and loss live.

Pack a whole project (or a snippet) into a single text ready to paste into an AI: removes comments, minimizes and shields secrets, IP and sensitive data. 100% in the browser — your code is never uploaded to any server.

Paste a document and measure how much of it you can throw away without losing a single idea. It compares paragraphs by MEANING with a model running in your browser, so it catches the padding that repeats the same thing in different words — exactly what a word-list detector misses. It strikes out what is redundant, points at the paragraphs that repeat each other and leaves you the core to copy. It does NOT tell you whether an AI wrote it: that cannot be validated. It measures emptiness, which belongs to the text and not to its author.

Analyse X.509 certificates in PEM format: subject, issuer, validity dates, SANs, key type and days remaining with a colour indicator.

Split group expenses and calculate who owes whom with the minimum number of transfers.

Train a character-level language model on YOUR text and generate new text in that style. Two modes: by counting (n-gram, instant) or with a neural network trained by gradient descent. Tune the temperature and watch the next-character probability, just like a real LLM. The n-gram mode is a character-level Markov; for chain theory (stationary, PageRank) see Markov chains.

Convert between availability percentage (99.9%, 99.99%…) and maximum downtime per hour, day, week, month and year.

Discover groups in unlabeled data (unsupervised learning) and compare k-means with DBSCAN live. Watch the centroids converge step by step, try "Moons" and "Rings" to see where k-means fails and DBSCAN succeeds, and tune k, eps and minPts.

Structurally compare two JSON objects and list added, removed and changed keys.

Beautify or minify SQL, CSS, HTML and JavaScript code with automatic indentation.

Generate real, elven, Norse, sci-fi or Japanese-inspired names. Copy all with one click.

Generate QR codes with size and error correction options. Download as PNG.

Classify your team as Elite / High / Medium / Low based on the four DORA metrics: deployment frequency, lead time, MTTR and change failure rate.

Detects and replaces sensitive data (emails, phones, validated cards, IBAN, national IDs, keys and secrets) with Presidio-style operators: replace, redact, mask, reversible token or hash. Ideal to clean logs or prompts before pasting them into an AI. 100% in the browser.

Of these passing tests, which ones cannot fail? Paste your test file and it tells you, case by case, what it really checks — with the evidence in front of you, so you can prove it wrong. And the part nobody else does: it compares the BEFORE and AFTER of a change and shows you whether you weakened the net — the matcher that got widened, the assertion that vanished, the case that stopped running. That is the cheap shortcut of someone in a hurry, and of an AI told to make the suite go green. TypeScript, JavaScript, Python, Java and Go. It runs nothing: your code never leaves the browser.

Three views on embeddings (meaning vectors): measure the cosine similarity between texts, project them to a 2D map with PCA and build a mini RAG that retrieves the most relevant chunks. All with models running in the browser.

Stopwatch with laps and history. Hundredths of a second precision and copy results button.