Tiny, open, native coding agent.

v0.0.8 (notes)6.01mibstatus: experimental use at your own risk, we will be making frequent changes

fx
This demo is available in browsers with WebAssembly JSPI support, like Safari 27+ and Chrome.

fx is a coding agent harness and CLI written in Zig, optimized for research and embeddability as part of larger systems.

It focuses on minimalism and performance across the board, from system prompt design to its tools, feature set, and 6.01 MiB binary.

Its output is closer to a Unix shell than an IDE in the terminal.

It is open source (Apache-2.0), model-agnostic, and suitable for both local and cloud inference.

Tiny native binary

Install one binary for your terminal, CI, or agent sandbox.

Fast startup

Start an interactive session or run a single request with fx ask. No background service is required.

WebAssembly support

Run the agent or terminal in the browser with libfx. Your application controls storage, tools, and network access.

Shell-like UI and ergonomics

fx preserves scroll history and keeps tool activity in the conversation. Open the full transcript when you need more detail.

Context efficient

Concise tool schemas keep the context small. Skill instructions and MCP tool schemas load when needed.

Embeddable and extensible

Embed the core with libfx, add your own tools, and connect skills or MCP servers.

Model and provider agnostic

Designed to work with local models, gateways, direct provider API access or subscriptions.