fx

fx is a coding agent harness and command-line interface written in Zig that helps developers work with AI in terminal-based workflows. It functions as a minimal tool designed for research and integration into larger systems, prioritizing simplicity and performance. The agent can work with local models, API gateways, and direct provider access, and is model-agnostic, meaning it works across different AI platforms. fx produces output that resembles Unix shell interactions rather than traditional IDE interfaces, preserving conversation history and keeping tool activity visible.

The tool is developed by vercel-labs and distributed under the Apache 2.0 license. It comes as a small native binary optimized for fast startup and can run in browsers via WebAssembly compilation. The agent is embeddable through libfx, allowing developers to incorporate it into their own systems and extend it with custom tools or connect external tool servers. Its design emphasizes efficiency in context usage and provides both interactive sessions and single-request operations through command-line arguments.