openclaw-antigravity-mcp

Use Claude & Gemini for free in Claude Code, Cursor, and any MCP client.

This is an MCP server that bridges Antigravity Claude Proxy — a local proxy that provides free access to Claude and Gemini models through your Google account — to any MCP-compatible AI coding tool.

What is Antigravity?

Antigravity Claude Proxy is a popular open-source npm package that runs a local API proxy on your machine. It uses your Google account to access Claude (Opus 4.6, Sonnet 4.6) and Gemini (3 Flash, 3 Pro) models at zero cost. The proxy exposes a standard Anthropic Messages API on localhost.

This MCP server is the bridge: it translates MCP tool calls from your coding tool into Antigravity proxy API calls, so you can use these models as native MCP tools.

┌─────────────────┐     stdio      ┌──────────────┐     HTTP       ┌──────────────────┐
│  Claude Code /  │ ◀──────────▶   │  this MCP    │ ◀──────────▶   │  Antigravity     │
│  Cursor /       │   MCP protocol │  server       │  localhost     │  Proxy (:8080)   │
│  Windsurf       │                │  (0 deps)    │                │  → Claude/Gemini │
└─────────────────┘                └──────────────┘                └──────────────────┘

Quick Start

1. Install & start Antigravity proxy

npm i -g antigravity-claude-proxy
acc accounts add     # add your Google account
acc start            # starts proxy on localhost:8080

2. Add to your MCP config

Claude Code — add to .mcp.json in your project root:

{
  "mcpServers": {
    "antigravity": {
      "command": "npx",
      "args": ["-y", "openclaw-antigravity-mcp"]
    }
  }
}

Cursor / Windsurf — same config in your MCP settings.

3. Verify

npx openclaw-antigravity-mcp --test

Output:

🛸 OpenClaw Antigravity MCP — Connection Test
   Proxy: http://localhost:8080

   [1/3] Health...  ✅ ok (1 account)
   [2/3] Models...  ✅ 6 models
          • claude-opus-4-6-thinking
          • claude-sonnet-4-6-thinking
          • claude-sonnet-4-6
          • gemini-3-flash
          • gemini-3-pro-low
          • gemini-3-pro-high
   [3/3] Chat...    ✅ Response: "ok"

   Result: ✅ All tests passed (3/3)

That's it. Your MCP client now has 5 AI tools powered by Claude and Gemini.

Tools

| Tool | What it does | |------|-------------| | chat | Chat with Claude or Gemini. Supports multi-turn conversations, system prompts, model selection, and temperature control. | | reason | Deep reasoning with extended thinking (chain-of-thought). For complex logic, math, and multi-step problems. | | code | AI code assistant — generate, review, debug, refactor, explain, or write tests. | | models | List all models available on your proxy. | | status | Check proxy health, account info, latency, and rate limits. |

Models

| Model ID | Description | |----------|------------| | claude-opus-4-6-thinking | Claude Opus 4.6 with extended thinking | | claude-sonnet-4-6-thinking | Claude Sonnet 4.6 with extended thinking | | claude-sonnet-4-6 | Claude Sonnet 4.6 (fast) | | gemini-3-flash | Gemini 3 Flash | | gemini-3-pro-low | Gemini 3 Pro | | gemini-3-pro-high | Gemini 3 Pro (high quality) |

Configuration

Custom proxy URL or API key via environment variables:

{
  "mcpServers": {
    "antigravity": {
      "command": "npx",
      "args": ["-y", "openclaw-antigravity-mcp"],
      "env": {
        "ANTIGRAVITY_URL": "http://localhost:3000",
        "ANTIGRAVITY_KEY": "my-key"
      }
    }
  }
}

| Variable | Default | Description | |----------|---------|-------------| | ANTIGRAVITY_URL | http://localhost:8080 | Antigravity proxy URL | | ANTIGRAVITY_KEY | (empty) | API key for the proxy |

Architecture

• Built with: TypeScript (strict mode), @modelcontextprotocol/sdk, Zod validation
• Transport: stdio (stdin/stdout JSON-RPC) via official MCP SDK
• Testing: 103 tests, 99.8% coverage (Vitest + v8)
• Retry: exponential backoff with jitter on 429/5xx (max 3 attempts)
• Network: only connects to your local Antigravity proxy (no external calls)
• Security: Zod validates all inputs; API keys and Google credentials never leave your machine

Troubleshooting

| Problem | Fix | |---------|-----| | Cannot connect to proxy | Run acc start to start Antigravity proxy | | Auth expired | Re-login in the Antigravity app, then restart proxy | | No models returned | Check acc accounts list — you need at least one Google account | | Timeout after 30s | Proxy may be overloaded — restart with acc start |

FAQ

Q: Is this actually free? Yes. Antigravity proxy uses your Google account's free-tier access to Claude and Gemini. This MCP server adds no cost on top of that.

Q: Is this safe? Yes. This server runs locally and only talks to localhost. It never contacts any external server. All inputs are validated with Zod. Review the source — it's fully typed TypeScript with 99%+ test coverage.

Q: What's the difference from using Claude API directly? The Claude API requires a paid API key. Antigravity proxy provides the same models through your Google account at no cost. This MCP server makes those models available as native tools in your coding environment.

License

MIT — OpenClaw Intelligence