fx

What it is

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 system prompt design, tools, feature set and a 7.8 MiB binary. For end users its CLI output style aims to be closer to a Unix shell than a heavy terminal IDE. It is open source under Apache-2.0, model agnostic, and suitable for both local and cloud inference.

Usage

Installation is via a setup script, after which a user signs in with Vercel or adds an AI Gateway API key through fx setup, then runs fx from a project directory where the current directory becomes the primary workspace. It lists saved sessions with fx sessions and resumes with fx session resume, supports a /feedback form and a /trace diagnostic, and starts in auto permission mode where routine development actions run directly and unresolved sensitive actions receive one bounded automatic review. JSON and quiet requests stay noninteractive by default.

Embedding

fx builds as a native binary or WebAssembly, and applications embedding it can provide network transport, session storage, configuration, permission handling and terminal I/O. Surfaces include fx acp to connect the native agent to Agent Client Protocol clients, createFxAgent to embed the agent core in a JavaScript host via fx-core.wasm, and createFxTerminal to embed the interactive terminal via fx-term.wasm. The WebAssembly SDK is marked experimental.

Editorial conclusion

fx is Apache-2.0 licensed and reported one thousand six hundred seventy eight stars at indexing, with the README marking the project as experimental and advising use at your own risk.