- 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 6.39mib binary.
- For end users, its CLI output style and form factor aims 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.
- Designed for instant installation and embedding in resource constrained environments and agent sandboxes.
- fx cold starts in 10µs and does no unnecessary work or I/O prior to accepting user input, making it ideal for programmatic use.
- Optimal fx.wasm builds produced by the Zig toolchain, which further reduce fx's size, making the network stack pluggable.
- fx contributes single-digit megabytes of memory baseline, allowing you to pack many instances in one machine.
- fx preserves scroll history by default, produces minimal output, and makes sparing use of complex TUI or paints
- Minimal system prompt and tools, to save on token costs and to yield optimal time-to-first-token performance (TTFT).
- Small core, extended via skills, plugins, MCPs, with a Unix-like philosophy to extensibility.
- Designed to work with local models, gateways, direct provider API access or subscriptions.