fx
Unix like coding agent
fx is a lightweight, open-source AI coding agent built in Zig that operates through a Unix-style command-line interface. Designed for research and embeddability, it delivers a minimalist 7.8 MiB binary optimized for performance with model-agnostic support for both local and cloud inference. The agent integrates authentication for Vercel AI Gateway, OpenAI Codex (ChatGPT subscriptions), and xAI Grok, while supporting MCP server connections, skills, and subagents for extensibility. Developers can use fx interactively for coding tasks, embed it via WebAssembly or Agent Client Protocol, or run single-shot commands for scripted workflows.
Key Features
Use Cases
- 01Interactive coding assistance in terminal environments with minimal UI overhead compared to IDE-based agents
- 02Embedding AI agent capabilities into JavaScript applications via WebAssembly SDK
- 03Connecting to editors and IDEs through Agent Client Protocol for standardized agent integration
- 04Scripted automation using single-shot 'fx ask' commands with JSON output for pipeline integration
- 05Research and experimentation with custom agent workflows through skills, MCP servers, and subagents
- 06Subscription-based AI access using existing ChatGPT or Grok accounts without separate API key management
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fx — FAQ
What is fx and what does it do?+
fx is a native AI coding agent delivered as a command-line tool that provides interactive coding assistance with minimal system overhead. It supports multiple AI model providers and can be embedded into larger applications or used standalone for development tasks.
How do I install fx?+
Run 'curl -fsSL https://fx.sh/setup.sh | bash' to install the binary. After installation, authenticate with 'fx login' for Vercel AI Gateway, 'fx login codex' for ChatGPT subscription access, or 'fx login grok' for Grok subscription access.
Which AI clients and model providers does fx support?+
fx works with Vercel AI Gateway (API key-based), OpenAI Codex (ChatGPT subscriptions), and xAI Grok (Grok subscriptions). It also connects to editors and IDEs via Agent Client Protocol (ACP) and can be embedded in custom applications.
Do I need API keys or subscriptions to use fx?+
You need either a Vercel AI Gateway API key, an eligible ChatGPT subscription, or an eligible Grok subscription. The Codex and Grok routes use OAuth authentication and never send tokens to third parties.
Is fx free and open source?+
Yes, fx is released under the Apache-2.0 license and is fully open source. However, you still need access to an AI model provider through API keys or subscriptions, which may have associated costs.
Can I extend fx with custom tools and skills?+
Yes, fx supports MCP server connections for external tools, a skills system for reusable instructions, and subagents for delegated work. You can add servers via 'fx mcp add' or workspace .mcp.json files, and skills via the skills directory.
How do I install fx?+
Open the source repository on GitHub and follow its README. fx is a agent — MCP Agents Market links you directly to the official repo.
Is fx free?+
fx is an open-source project hosted on GitHub. Check the repository for its license and any usage requirements.