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

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.

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

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.

List saved sessions with fx sessions. Resume the latest session for the current workspace, or select an exact session ID, through the same command group:

fx session resume last
fx session resume --id <id>

Each interactive session names its terminal tab. The title prefers the session name, falls back to the workspace name, and keeps the active model as secondary context. Renaming or resuming a session updates the tab, and exiting clears the fx-owned title. Noninteractive commands do not emit terminal-title controls.

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. Routine understood development actions run directly; unresolved sensitive actions receive one bounded automatic review. A blocked action may return an exact approval request that the agent can send to fx's real permission screen. Ordinary question text never grants permission. See Permissions for other modes and persistent rules.

JSON and quiet requests stay noninteractive by default. Add --prompt-permissions to allow the existing Y/N approval prompt when stdin is a TTY. Prompt text is written to stderr, so JSON stdout stays parseable and quiet stdout stays empty. Piped or redirected stdin remains noninteractive and fails instead of waiting for approval.

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.

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.

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. Skills installed via symlinks that resolve outside home or workspace (e.g. Nix store paths) are loaded when their resolved target is inside a directory listed in the FX_SKILL_SYMLINK_AUTHORITIES environment variable (colon-separated absolute paths). fx status and fx doctor report an invalid trusted MCP profile without starting its servers.

Read the fx documentation.

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.

Apache-2.0

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

Interface sounds by cuelume.