fx

fx is an open source coding assistant that runs as a small native program in your terminal and connects to local or cloud models. It's aimed at developers who prefer a shell-style interface, and researchers building agents into larger systems. Written in Zig and licensed under Apache 2.0, it runs without a background service.

You can connect it to Ollama through an OpenAI-compatible endpoint, use OpenRouter or Vercel AI Gateway, or access models through ChatGPT and Grok subscriptions. The agent runs on your machine; inference runs at the endpoint you choose. A local model connection keeps inference local, while a cloud connection sends model requests to that service.

The terminal interface preserves scrollback and shows tool activity alongside the conversation, with a full transcript available for closer inspection. fx supports interactive work and individual requests for scripts or CI. Its concise tool definitions keep context use small, and it loads skill instructions and MCP tool definitions when they're needed. Skills, MCP servers, custom tools and subagents extend what it can do.

For developers embedding an agent, libfx exposes the core and interactive terminal, while Agent Client Protocol support connects the native agent to compatible editors. fx also runs as WebAssembly in the browser. Applications that embed it control storage, permissions, tools and network access; the website's browser demo uses a browser workspace, while the native CLI works with your own files.