A 7.8 MiB coding agent that acts like a shell, not an IDE

What it does fx is a coding agent harness and CLI written in Zig. It runs as a 7.8 MiB native binary or compiles to WebAssembly, offering a shell-style interface instead of the typical full-screen TUI. The tool is model-agnostic and supports both local and remote inference.

The interesting bit While most agents try to become your IDE, fx tries to become plumbing. It exposes separate WebAssembly surfaces for the agent core and interactive terminal, and its permission system uses bounded automatic review with exact rule matching rather than broad trust prompts.

Key highlights

• 7.8 MiB binary emphasizing minimalism in prompts, tools, and features
• Model-agnostic architecture supporting local and cloud inference
• Embeddable as native code or WebAssembly (fx-core.wasm, fx-term.wasm)
• Permission system with bounded automatic review and persistent exact rules
• Extensible via skills, MCP servers, and subagents

Caveats

• Explicitly marked experimental by the maintainers
• WebAssembly SDK is experimental
• Requires Vercel authentication or an AI Gateway API key to operate

Verdict Best suited for developers building agent-driven workflows or editor integrations that need a small, hackable core; avoid if you want a mature, fully standalone CLI with no vendor account requirements.