fx :Tiny, open, native coding agent.

fx is an experimental, open-source coding agent and CLI written in Zig, designed for research and embeddability in larger systems. The codebase is optimized for minimalism and performance, with the binary size being just 6.39mib. fx focuses on providing a Unix-like experience within a terminal, with a CLI output style that is more akin to a traditional Unix shell. It is model-agnostic and suitable for both local and cloud inference, making it versatile for various deployment scenarios.

One of fx's standout features is its lightning-fast cold start time of just 10µs, which allows it to accept user input immediately and without any unnecessary work or I/O. This makes it ideal for programmatic use in resource-constrained environments and agent sandboxes. The binary size of fx is further reduced by building it with the Zig toolchain, resulting in optimal network stack pluggability. Additionally, fx preserves scroll history by default, produces minimal output, and uses sparing complex TUI or paints.

All aspects of fx, including the networking and SDK, are configurable in the documentation, giving users the flexibility to tailor the agent to their specific needs. fx preserves scroll history by default, producing minimal output, and uses sparing complex TUI or paints. The small core of fx can be extended via skills, plugins, and MCPs, following a Unix-like philosophy of extensibility. fx is designed to work seamlessly with local models, gateways, direct provider API access, or subscriptions.