Simon Willison @simonw ↗

Quickly sandbox your AI agent.

Docker Sandbox Kit Specification v3 - the kit descriptor grammar, the OCI artifact, the build frontend, and the conformance suites

Application Kernel for Containers

Turn any idea, plan, or codebase into a beautiful interactive diagram. An agent skill for Claude Code, Codex, and more.

A compute toolkit for the web with the depth of Plan 9 from Bell Labs

Monkey patch, test, and trace Python by attaching bindings to call sites, without modifying the code being observed. Built on wrapt.

Native LLM inference server for Apple Silicon. OpenAI + Anthropic API compatible. No Python. Zig backend, Swift frontend macOS app with chat, music, voice, video generation.

A Bun CLI that ingests Claude Code and Codex session transcripts, generates LLM-powered daily summaries, and serves a browsable web UI for your engineering journal.

Autonomous CTF solver that races multiple AI models in parallel. 1st place BSidesSF 2026.

Sandbox your local AI agents so they can read/write only what they need

Convert Word, PowerPoint, Excel, OpenDocument, RTF, EPUB, CSV, and PDF to clean Markdown. Built in Rust, with Node.js and Python bindings.

A fully procedural first-person jungle in Three.js. Zero external art assets - every texture, mesh and sound generated in code.

Deploy an AI-generated backend for every user.

Find the test that's leaking before the one that fails

Minimal WebGL Library

Rhai - An embedded scripting language for Rust.

A collection of notebooks/recipes showcasing some fun and effective ways of using Claude.

ExploitGym is a large-scale, realistic benchmark built from real-world vulnerabilities designed to evaluate AI agents' ability to develop exploits.

Local AI, native to your Mac. Chat, serve, monitor, and connect MLX models from one macOS app.

ggml speech-to-text inference for 16+ model families

Tiny, fast, Linux-compatible sandboxes. Powered by WebAssembly.

WebKit compiled to WebAssembly: a full browser engine running inside a browser tab, rendering to canvas, networking over Wisp.

(Still experimental) Real Goroutines for Python 3.13t+ free-threaded.

SpaceXAI's coding agent harness and TUI. Fullscreen, mouse interactive, extensible.

A flight-compliant WebAssembly interpreter.

A native macOS UI for Apple's platform

A data-structure parameterization system written for embedding context in JSON objects

The programming language for agents

an implementation of the ideas in Erik Meijer's "Guardians of the Agents: Formal Verification of AI Workflows" (Communications of the ACM, January 2026)

Political Compass for AI

MDN's prototype MCP server

Cross-platform WebDriver server for Tauri applications (Linux, macOS, Windows)

fast ast walk

Your CLI home video recorder 📼

Turn a terminal session into a good-looking animated GIF. A vhs wrapper with an attractive default look.

Python library for running a MicroPython sandbox using WebAssembly

Sandboxed tools and JS runtime for AI agents

Finds potential accessibility gaps, files GitHub issues to track them, and attempts to fix them with Copilot.

Thin Python wrapper of quickjs-ng

Observable Plot charts for Datasette Agent

An LLM-powered agent for Datasette

Universal Rust multiplexer with a typed SDK — drive any CLI or TUI app from code. Native on Linux, macOS, and Windows.

Data collection and analysis for a PyCon talk on GitHub Actions security across Python packages.

PyPI downloads analytics dashboard

A tool for measuring Python class cohesion.

Automation foundation model for tiny devices: 2-bit, 8-29 MB, tool calls, ASR, structured extraction and embeddings on phones, wearables, smart homes, robots, cars and microcontrollers.

Code that accompanies the paper release for "LLMs Corrupt Your Documents When You Delegate"

Continuous background code review database for agents, work faster and smarter with accountability for every line of generated code.

DeepSeek 4 Flash and PRO local inference engine for Metal, CUDA and ROCm

PyWry is a cross-platform app factory, rendering engine and UI toolkit for Python that produces native desktop, web, and notebook experiences from a single API.

A fast, helpful, and open-source document parser

Experiments with GitHub event data

A format specification for describing a visual identity to coding agents. DESIGN.md gives agents a persistent, structured understanding of a design system.

This is a collection of the best SVG images of pelicans riding bicycles.

Original Apollo 11 Guidance Computer (AGC) source code for the command and lunar modules.

An embeddable, portable, branchable virtual machine to safely run Agents locally.

A friendly library for working with PDFs

Fine-tune Gemma 4 and 3n with audio, images and text on Apple Silicon, using PyTorch and Metal Performance Shaders.

The best-benchmarked open-source AI memory system. And it's free.

CLI tool for saving a faithful copy of a complete web page in a single HTML file (based on SingleFile)

Fast, accurate & comprehensive text measurement & layout

JSONata for Python

Drop-in replacement for Requests. Automatic HTTP/1.1, HTTP/2, and HTTP/3. WebSocket, and SSE included. WASI Supported.

Fyn is a fork of uv for fast Python package management, dependency resolution, virtual environments, and pyproject.toml workflows.

Traccar reverse geocoding service

Distributed Python made simple.

Running a big model on a small laptop

A fast parser, formatter, static analyzer, and language server for SQLite SQL.

Lightpanda: the headless browser designed for AI and automation

Snapshotable WebAssembly interpreter from scratch. Includes a time travel debugger

Documentation that simply works

Open-source Agent Operating System

Python bindings for Luau

A small, fast, and embeddable programming language based on Lua with a gradual type system.

argparse + https://usage.jdx.dev/

Local-first session search, analytics, insights, and token use statistics for coding agents, supporting Claude Code, Codex, and more than 20 other agents.

Google Workspace CLI — one command-line tool for Drive, Gmail, Calendar, Sheets, Docs, Chat, Admin, and more. Dynamically built from Google Discovery Service. Includes AI agent skills.

Lightweight Django middleware for APM-style request profiling (DB vs App time, query count)

The control room for your Django app

Give your agents the power of the Hugging Face ecosystem

A tool for analyzing the size of compiled Go binaries, offering cross-platform support, detailed breakdowns, and multiple output formats.

Ultra-lightweight, zero dependency, semantic HTML, CSS, JS UI library. ~10KB min+gz.

A lightweight, lightning-fast, in-process vector database

A port of Descent to Three.js.

SeaweedFS is a distributed storage system for object storage (S3), file systems, and Iceberg tables, designed to handle billions of files with O(1) disk access and effortless horizontal scaling.

SCAM - Security Comprehension Awareness Measure | Open-source benchmark that tests AI agents' security awareness during realistic, multi-turn workplace tasks.

python sqlite driver

A secure Python sandbox, written in Rust, for code written by AI.

Pure C inference of Mistral Voxtral Realtime 4B speech to text model

Claude Opus 4.6 wrote a dependency-free C compiler in Rust, with backends targeting x86 (64- and 32-bit), ARM, and RISC-V, capable of compiling a booting Linux kernel.

A file server that supports static serving, uploading, searching, accessing control, webdav...

tinyproxy - a light-weight HTTP/HTTPS proxy daemon for POSIX operating systems

🔒🐧 Run command in a secure native sandbox (zero deps)

HTTP proxy that injects 3rd party credentials into requests

Binary package factory

Easy Linux virtual machine on MacOS to sandbox LLM agents.

My collection of Claude skills

Lightweight WASM-based Linux VM for AI agents - run shell commands in an isolated Alpine Linux environment

A Python sandbox using Wasmtime

Flux 2 image generation model pure C inference

Sandbox for Agents

One from scratch browser built by one human and one agent, working hand in hand

Cowork-like experience in the browser using filesystem api

State-of-the-art 2D and 3D Face Analysis Project

Scalable real-time messaging server in a language-agnostic way. Self-hosted alternative to Pubnub, Pusher, Ably, socket.io, Phoenix.PubSub, SignalR. Set up once and forever.

A radically modular HTML/CSS rendering engine

Random digital audio effects

Zero heap allocation HTTP server using OxCaml. v experimental!

A fast TCP/UDP tunnel over HTTP

A fast reverse proxy to help you expose a local server behind a NAT or firewall to the internet.

A Claude Code plugin + Agent Skill + MCP Server for analyzing Federal Election Commission (FEC) campaign finance filings.

Optimized string search routines for Rust.

A single page printable calendar

μSQLite library module for MicroPython

Brython (Browser Python) is an implementation of Python 3 running in the browser

The verification layer for coding agents

Modern JavaScript runtime in Python, powered by V8 and bridged by Rust

A minimalist text editor that lives in URL

The repository provides code for running inference with the Meta Segment Anything Audio Model (SAM-Audio), links for downloading the trained model checkpoints, and example notebooks that show how to use the model.

Swift-JustHTML a Swift port of EmilStenstrom/justhtml by implementing 100% html5 spec compliant parsing of html documents in pure Swift

weird LLM-translated mutant smb server experiment / bad idea

A pure Python HTML5 parser that just works. No C extensions to compile. No system dependencies to install. No complex API to learn.

AXe is a CLI tool for interacting with Simulators using Apple's Private Accessibility APIs.

Migrate a project from Poetry/Pipenv/pip-tools/pip to uv package manager

An example of using uv in Docker images

Minimal CLI coding agent by Mistral

Local-first development platform

Generation of diagrams like flowcharts or sequence diagrams from text in a similar manner as markdown

The original ABC language (Python's predecessor), from 1991

A dynamic library providing Virtualization-based process isolation capabilities

A lightweight sandboxing tool for enforcing filesystem and network restrictions on arbitrary processes at the OS level, without requiring a container.

Ruby 3.4.7/4.0.0 port to Cosmopolitan Libc - Actually Portable Ruby

An open-source database of AI models.

Orchestrate Claude, Codex and Grok in one app. Open-source (MIT), reuses the subscriptions you already pay for.

HTTP API for Claude Code, Goose, Aider, Gemini, Amp, and Codex

HLS.js is a JavaScript library that plays HLS in browsers with support for MSE.

Embeddable v86 virtual machines

WebAssembly (Wasm) arch support for the Linux kernel

An experiment in durability

A GitHub Action that runs a command in a gVisor sandbox

Gemini CLI Tips and Tricks

Leash by StrongDM - take your AI agents for a walk

Welcome to your Hackable Conference Badge

Plano is an AI-native proxy server and data plane for agentic apps. Smart LLM routing, observability, agent orchestration, and guardrails so you stay focused on your agents core logic.

Ham exam practice app

A Swift package for parsing iWork Keynote, Pages, and Numbers documents

The best ChatGPT that $100 can buy.

Tauri binding for Python through Pyo3

Code and data for the paper "Large Language Models Achieve Gold Medal Performance at the International Olympiad on Astronomy & Astrophysics (IOAA)" (https://arxiv.org/abs/2510.05016).

An agentic skills framework & software development methodology that works.

RSS reader for macOS and iOS.

CRDTs based on Yrs.

WebSocket Connector for pycrdt

Useful extensions to the standard Python datetime features

A docker container that jails an LLM CLI like codex, gemini, or claude code.

SQLite-Vector is a cross-platform, ultra-efficient SQLite extension that brings vector search capabilities to your embedded database.

A single-node analytical database engine with geospatial as a first-class citizen

JavaScript/TypeScript-native, low-boilerplate, object-capability RPC system

SWE-Bench Pro: Can AI Agents Solve Long-Horizon Software Engineering Tasks?

HTTP(s) request filter for processes

Extract and compare system prompts and tools from different Claude Code versions

Running TCP/IP over SWD lines

DSPY on action with OpenSource LLMs.

A platform for hosting interactive workshop environments in Kubernetes, or on top of a local container runtime.

Under 1KB each! Super Tiny Icons are miniscule SVG versions of your favourite website and app logos

tfw when you when your lid when uhh angle your lid sensor

zero-dependency image processing library

An implementation of Django's EmailBackend compatible with sendgrid-python v5+

A collection of Dev Container Features managed by Dev Container spec maintainers. See https://github.com/devcontainers/feature-starter to publish your own

Jan is an open source alternative to ChatGPT that runs 100% offline on your computer.

Qwen-Image-Lightning: Speed up Qwen-Image model with distillation

Wassette: A security-oriented runtime that runs WebAssembly Components via MCP

Renderer for the harmony response format to be used with gpt-oss

[ICLR2026] Test-Time Scaling with Reflective Generative Model

Go sqlite3 http vfs: query sqlite databases over http with range headers

MLX Omni Server is a local inference server powered by Apple's MLX framework, specifically designed for Apple Silicon (M-series) chips. It implements OpenAI-compatible API endpoints, enabling seamless integration with existing OpenAI SDK clients while leveraging the power of local ML inference.

slime is an LLM post-training framework for RL Scaling.

Ever used asyncio and wished you hadn't? A tiny (~400 lines) event loop for Python.

Build an agent harness and control it end-to-end. Open-source SDK for production AI agents in Python & TypeScript - any model, any cloud.