Coding agent · CLI / WASM

fx

Verified Aug 2026

Quick answer: Terminal-first users who want a tiny embeddable Zig coding agent (CLI, ACP, WASM) with AGENTS.md/skills/MCP — closer to a Unix shell than a heavy TUI or IDE fork.

Best for

Terminal-first users who want a tiny embeddable Zig coding agent (CLI, ACP, WASM) with AGENTS.md/skills/MCP — closer to a Unix shell than a heavy TUI or IDE fork.

Skip if

You need Windows-native installs, classic multi-lab BYOK without Vercel AI Gateway, or a battle-tested IDE/TUI (Cursor / Claude Code / Crush).

Who it fits

  • Terminal-first users who want a tiny embeddable Zig coding agent (CLI, ACP, WASM) with AGENTS.md/skills/MCP — closer to a Unix shell than a heavy TUI or IDE fork.
  • Terminal-first engineers who live in the shell and git
  • Builders who start in the browser without a local IDE setup
Experimental

Pros

Tiny ~6.4 MiB Zig coding agent with ~10µs cold start and single-digit MB baseline — built to embed in sandboxes and pack many local instances; shell-like CLI (not a heavy TUI) plus ACP for editors, `fx ask` headless, and an experimental WASM SDK; first-class AGENTS.md (global, workspace, and target-scoped), SKILL.md discovery across Claude/Codex/OpenCode/agents dirs, MCP, and session-backed subagents; context-efficient prompt/tools for cheaper TTFT; permission modes with a command sandbox.

Cons

Officially experimental (v0.0.x) with frequent breaking changes; auth and the model catalog currently go through hosted Vercel AI Gateway (login or gateway key), not OpenCode-class keys you paste for every lab; native install is macOS/Linux only; WASM embed drops native MCP, skills, subagents, and OS sandbox vs the local CLI.

Facts

Locality:
Hybrid (local + cloud)
Surfaces:
CLI, Web
Maturity:
Experimental
Open source:
Source available
Free tier:
Free option available
MCP:
Model Context Protocol support
Verified:
Aug 2026

Agent standards & memory

AGENTS.md: Full SupportSKILL.md: SupportedRules / memory: ~/.fx/AGENTS.md plus workspace and target-scoped AGENTS.md; skills catalog; MCP; saved sessions with resume/compaction; permission/sandbox grants.100% Free (Open-source, Apache-2.0); model spend via Vercel login or AI Gateway key.

Compare one neighbor first

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Alternatives

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