⠀⠀⠀⠀⠀⠀⣠⣾⣿⣿⣿⠀⠀⠀⠀⠀⠀⠀⠀
 ⠀⠀⠀⠀⠀⢰⣿⡿⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
 ⠀⠀⠀⣠⣶⣿⣿⣷⣶⡶⣶⣶⣆⠀⠀⠀⣴⣶⣶⠆
 ⠀⠀⠀⠉⢹⣿⣿⠉⠉⠀⠘⢿⣿⣧⣀⣾⣿⡿⠃⠀             Tiny, open, embeddable, native coding agent.
 ⠀⠀⠀⠀⣼⣿⡏⠀⠀⠀⠀⠀⠻⣿⣿⣿⠟⠀⠀⠀
 ⠀⠀⠀⢀⣿⣿⠃⠀⠀⠀⠀⢠⣦⠘⢿⣿⣷⡀⠀⠀             curl -fsSL https://fx.sh/setup.sh | bash
 ⠀⠀⠀⣸⣿⡟⠀⠀⠀⠀⣰⣿⣿⠗⠀⠻⣿⣿⣄⠀
 ⠀⠀⠀⣿⣿⠇⠀⠀⠀⠾⠿⠿⠋⠀⠀⠀⠘⠿⠿⠦             ⚠ Status: Experimental. Use at your own risk.
  ⠀⣸⣿⡿⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀
 ⣿⣿⣿⠟⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀

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 7.8 MiB binary.

For end users, its CLI output style and form factor aim to be closer to a Unix shell than a heavy "IDE in the terminal" TUI.

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

Install

curl -fsSL https://fx.sh/setup.sh | bash

Run fx

To get started, sign in with Vercel:

fx login

Or add an AI Gateway API key:

fx setup

Run fx from a project:

cd your_project
fx

The current directory becomes the primary workspace. Enter a prompt, or run /help to browse interactive commands.

Run /feedback to open the feedback form at fx.sh/feedback. It does not create a diagnostic or change the clipboard.

Run /trace to create a private Markdown diagnostic with logs, session context, runtime state, permissions, and recent activity. On macOS, fx copies the .md file to the clipboard; on other platforms, it saves the file and prints its path. Review and redact the trace before sharing it.

Use fx ask for a single request:

fx ask "explain the changes in this repository"

fx starts in auto permission mode, which reviews unresolved sensitive actions. See Permissions for other modes and persistent rules.

Inside a saved session, /permissions remember <allow|deny> <tool-name> <arguments-json> stores an exact confirmed rule without running the action. /permissions lists stable rule IDs, and /permissions revoke <rule-id> removes a stored rule even when its original workspace or file state has changed.

Embed fx

fx builds as a native binary or WebAssembly. Applications embedding fx can provide network transport, session storage, configuration, permission handling, and terminal I/O.

The WebAssembly SDK is experimental. See the WebAssembly SDK and ACP documentation.

Extend fx

Add reusable instructions with skills, connect external tools through MCP, or delegate independent work to subagents. Project instruction files may link within their scope, and read-only workspace or compatibility skill directories may link within their owning workspace or home; managed skills, SKILL.md files, resources, and escaping links remain no-follow. fx status and fx doctor report an invalid trusted MCP profile without starting its servers.

Documentation

Read the fx documentation.

Build from source

Building fx requires Zig 0.16.0+:

git clone https://github.com/vercel-labs/fx.git
cd fx
zig build -Doptimize=ReleaseSafe
./zig-out/bin/fx

Run the test suite with zig build test. See CONTRIBUTING.md for development and contribution guidelines.

License

Apache-2.0

Third-party licenses and attributions are listed in THIRD_PARTY_NOTICES.md.

Credits

Interface sounds by cuelume.