# Vercel fx fx is a coding agent CLI from [[Vercel]] Labs, written in Zig. The pitch fits in one line: "Tiny, open, embeddable, native coding agent." The whole thing is a ~6 MB binary, Apache-2.0 licensed, and it runs on macOS and Linux. It's still experimental (v0.0.x at the time of writing), and Vercel says it plainly: use at your own risk, expect frequent changes. Install: `curl -fsSL https://fx.sh/setup.sh | bash`. Then `fx` in a project folder for the interactive shell, or `fx ask "..."` for one-shot requests in scripts. Not to be confused with Anton Medvedev's `fx`, the terminal JSON viewer (fx.wtf). ## A shell, not an IDE Most coding agents want to be your IDE inside the terminal. fx goes the other way: it behaves like a Unix shell. Output renders inline and your scrollback stays intact. That sounds minor, but if you live in the terminal, it really is a big deal. The more interesting angle is embeddability. fx is designed as an [[AI Agent Harness]] that you drop into larger systems, not just a tool you type into: - `fx acp` connects it to editors and any [[Agent Client Protocol (ACP)]] client - `createFxAgent()` embeds the agent core in a JavaScript host via `fx-core.wasm` - `createFxTerminal()` embeds the full interactive terminal via `fx-term.wasm` - The SDK ships on npm as `libfx`, with Node.js, browser, Next.js and Nuxt examples The host application can provide its own network transport, session storage, configuration, permission handling and terminal I/O. The fx.sh homepage demo actually runs the complete CLI as WebAssembly in your browser, with networking delegated to `fetch`. That's a nice proof of the design. ## Models and extensions fx is model-agnostic. You can sign in with the [[Vercel AI Gateway]] (`fx login`), a [[ChatGPT]] subscription through Codex OAuth (`fx login codex`), a [[Grok]] subscription (`fx login grok`), or point it at any OpenAI-compatible endpoint like [[Ollama]] or [[OpenRouter]] via named connections in `~/.fx/settings.json`. When going through the AI Gateway, you can even set provider routing order (e.g., try Bedrock first, then Anthropic). It supports the usual extension points: [[AI Agent Skills|skills]], [[Model Context Protocol (MCP)|MCP]] servers and subagents. There's also a Slack bot integration. Small detail I appreciate: every docs page is available as Markdown by appending `.md` to the URL, and there's an `llms-full.txt` with everything. Docs written for agents, not just humans. ## My take fx competes less with [[Claude Code]] than with harnesses like [[Pi Mono]]: small, hackable cores meant to be composed into your own tooling. The fact that the same binary targets native and WebAssembly opens doors (agents running in the browser, in sandboxes, inside other apps). Too early to bet on it, but worth watching. ## References - https://fx.sh/ - https://fx.sh/docs - https://github.com/vercel-labs/fx ## Related - [[Vercel]] - [[AI Agent Harness]] - [[Codex CLI]] - [[Vercel Open Agents]]