A collection of small, single-file web tools that run entirely in your browser.
Try the tools yourself here: https://www.codercowboy.com/demo/claude-tools/
Developers and designers who want quick, offline, no-signup utilities that run in the browser and never phone home.
If you'd rather have these as a CLI, a browser extension, or a polished hosted app with accounts and history, this isn't that. The Alternatives doc points you at tools that might fit better.
| Tool | What it does |
|---|---|
| ascii-art | Turn an image into text art in four modes - ASCII ramp, Unicode half-block, Braille, and colored ANSI - and export as plain text, colored HTML, or ANSI. Everything runs in the browser through the canvas; nothing is uploaded. |
| barcode-generator | Generate Code 128, EAN-13, UPC-A, and Code 39 barcodes with a live preview. Check digits are computed or verified, and the result exports as SVG or PNG. Nothing leaves the browser. |
| base64-tool | Base64 / data-URI encoder and decoder. Text or a file in; Base64, Base64URL, a data: URI, or a JS snippet out, and decode back. |
| batch-watermark | Stamp a text or logo watermark on many images at once, preview it on one, and export the batch as a zip. Size, margin, and spacing are percentages of each image's short side, with a nine-point anchor grid, opacity, rotation, and tiling. Output is PNG, JPEG, or WebP, and nothing leaves the browser. |
| color-converter | Batch-convert a pile of mixed rgba()/hex colors into one format. Paste them, see a swatch of each, copy them out. |
| color-designer | Color-scheme generator from HSL harmonies, optionally flavored by a mood. Roll five schemes, expand into a live demo, copy them out. |
| color-picker | Sample exact pixel colors out of an image. Load it, pan and zoom, eyedrop the pixel as rgba() and hex. |
| cron-builder | Build, parse, and understand a cron expression. Synced field pickers and raw editor, a plain-English explanation, and the next 5 fire times. |
| diff-viewer | Visual diff of two texts. A hand-rolled Myers diff shows changes side-by-side or inline with word-level highlighting, plus a copyable unified diff. Nothing leaves the browser. |
| dither-studio | Reduce an image to a limited color palette with optional dithering and chunky pixels, compare against the original with a before/after wipe, and export a PNG, an indexed PNG-8, or the palette. Everything runs in the browser through the canvas; nothing is uploaded. |
| format-converter | Convert a document between JSON, CSV, TSV, YAML, .properties, and XML, with auto-detect of the source format. Every parser and emitter is hand-rolled, and nothing you paste leaves the browser. |
| hasher | Hash text or a file - MD5, SHA-1, SHA-256, SHA-512, and CRC32 all at once, plus keyed HMAC, with optional Base64 output. Everything runs in the browser; nothing is uploaded. |
| hat-picker | Random picker for game night. Add entries, pull a winner from the hat with a slot-machine reveal and confetti, optionally removing each winner after the draw. |
| http-headers | Explain, lint, and build HTTP headers. Paste a raw request or response and get each header explained and checked against a security checklist with ready-to-paste fixes, or build a recommended set as plain text or an nginx, Apache, or Express snippet. Nothing is sent anywhere. |
| inflation-calculator | What a US dollar amount from one year is worth in another, using bundled BLS CPI-U annual data. |
| invisible-chars | Detect, reveal, and strip invisible, zero-width, bidi, and look-alike Unicode in pasted text. Flagged characters become colored chips with a per-character inspector, and a clean step normalizes and removes chosen categories. Nothing leaves the browser. |
| markdown-previewer | Live Markdown previewer. Type Markdown on the left and see the rendered HTML on the right. The converter is hand-rolled, sanitizes links and raw HTML, and nothing you type leaves the browser. |
| network-toolkit | Transfer-time math, CIDR/subnet math, IPv4/IPv6 conversion, and netmask ⇄ prefix. No DNS, no network calls. |
| pretty-printer | Pretty-print or minify JSON, YAML, HTML, CSS, SQL, and JavaScript. Every formatter is hand-rolled in vanilla JS, and nothing you paste leaves the browser. |
| qr-generator | Generate a QR code from text or a URL with a QR encoder hand-rolled in vanilla JS. Download it as PNG or SVG. |
| social-card-maker | Compose a social share image (Open Graph / Twitter card) from a title, subtitle, and solid, gradient, or photo background, with an optional logo. Export PNG, JPEG, or WebP and copy the matching meta tags. Everything runs in the browser through the canvas; nothing is uploaded. |
| uuid-generator | Generate and inspect identifiers - UUID v4/v7, ULID, nanoid, and random tokens - bulk generate and copy, plus an inspector. |
The whole set also has a little landing gallery at src/gallery/index.html.
Simply download this project's source code from github, and open src/gallery/index.html in your browser by double clicking on it in your file explorer (or finder), or drag it onto your browser window. If you have Node installed, npx ct run opens that gallery for you.
Want to rebuild the tools, run the tests, or use claude-tools as a baseline for your own project? You'll need Node.js 20+. Everything runs through ct, the repo's small command runner, driven straight from a clone with npx.
# Clone and install - one root node_modules holds all the dev/test deps
git clone https://github.com/codercowboy/claude-tools.git
cd claude-tools
npm install
npx playwright install chromium # the browser the e2e tests drive
# Then drive it with ct:
npx ct build [tool] # assemble every tool's index.html (or just one) from source/
npx ct dist # build, then assemble a deployable dist/ (gallery + one folder per tool)
npx ct test [tool] # run the whole suite (or one tool's unit + e2e)
npx ct serve [tool] # serve a tool (or the whole gallery) at http://localhost:8080
npx ct run # open the built gallery in your default browsernpx ct with no verb prints the menu. You only need npx ct build after editing a tool's source/ - the committed index.html files are already built.
The built tools are static index.html files with everything inlined, so once you're happy with one you can drop it on any static host - GitHub Pages, an S3 bucket, Netlify, a folder on your own web server - and it'll run there the same way it runs from file://. Nothing to configure, no backend to stand up.
For the whole set at once, npx ct dist assembles a dist/ folder - the gallery at dist/index.html, each tool under its own dist/<tool>/ - that you can deploy as-is to a static host like GitHub Pages. It's a copy of the built files, so the source tree is left alone.
Each tool is authored in pieces under a source/ folder and assembled by a small Node build (scripts/build-tool.mjs) into the single committed index.html. The result inlines all its own CSS and JS, so there's nothing to fetch at runtime and nothing to install to use it. There are zero packaged runtime dependencies - the only dev dependency is the test harness, and it never ships in the tool.
The full write-up - the build pipeline, the single root install, the shared includes, the two-layer testing, and the dependency breakdown and toolkit - lives in Technical details.
These aren't the only offline browser tools out there, and for some jobs a CLI or a purpose-built app beats a single HTML file. If one of these isn't your fit, the Alternatives doc names the closest analogs, the online tools they replace, and where to look when you want more.
Code & docs: Claude (Anthropic). Full transparency, Claude wrote all of it.
Concept & direction, the ideas guy: Jason Baker.
MIT - it's a great license because it gets out of your way: use it however you want, commercial or not, just keep the notice. My code should work, but I'm not liable if it goes sideways on you.
Questions, comments, kudos, criticisms - all welcome. — Coder Cowboy