Simon Willison's Tools

About

Simon Willison's Tools is a free, ever-growing collection of small single-page utilities that run entirely in your browser. There are more than 240 of them: image resizers and croppers, a QR code generator, a GeoJSON viewer, a LaTeX renderer, a Markdown previewer that renders SVG, HTML-table and rich-text-to-Markdown converters, a video compressor, token counters, and playgrounds for various AI APIs. It is for developers, writers and tinkerers who want a quick tool that just works, with no install, sign-up or upload to someone else's server. The site is run by Simon Willison, co-creator of Django and creator of Datasette, and one of the most widely read writers on practical LLM use. He describes it as an experiment in prompt-driven development with very low stakes. Almost every tool was written by prompting Claude, and lately also models like GPT and Gemini, and then iterating on the result. The colophon is what makes the project special: it lists every tool's commit history, often with a link to the exact chat transcript that produced the code. That makes it a working museum of what vibe coding can and cannot do. Highlights: • More than 240 tools, with new ones added most weeks • Each tool is a single HTML and JavaScript page, and most process your files locally in the browser • A colophon that shows each tool's commits and links to the LLM transcripts behind them • Media utilities such as an image resizer, a social-media cropper, a photo scrubber and a video compressor • Developer helpers such as a GeoJSON viewer, Mermaid and LaTeX renderers and a Claude token counter • Live playgrounds for AI APIs such as Gemini TTS, Gemini Live and OpenAI WebRTC • A companion set of Python tools Everything is free to use in any modern browser. The source code is on GitHub at simonw/tools under the Apache 2.0 license. A few AI playgrounds ask you to supply your own API key.

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