antigravity-claude-mcp

Give Claude Code a second brain. Ask Google Antigravity — Gemini 3 Pro, Claude, or GPT-OSS — for an independent code review or second opinion, right from inside Claude Code. One command. Zero dependencies.

claude mcp add antigravity -- npx -y antigravity-claude-mcp

That's it. Restart Claude Code, and Claude can now call ask_antigravity to get a second model's take on any plan or diff.

Why

Claude reviewing its own code is Claude reviewing its own code. You don't catch your own blind spots by thinking harder — you catch them with a different mind.

This bridges Claude Code to Google Antigravity's CLI (agy), so Claude can hand a plan or a diff to a different model family (Gemini 3 Pro by default) and get an independent verdict — before you do. Two models check the work; you make the call.

It's the wiring behind a simple loop:

You ── prompt ──▶ Claude validates ──▶ asks Antigravity (Gemini) ──▶ they agree on ONE plan
                                                                          │
        you approve ◀── Antigravity reviews the diff ◀── Claude writes the code

See examples/CLAUDE_ANTIGRAVITY_LOOP.md for the full working agreement you can drop into any project.

Quickstart (2 minutes)

1. Install the Antigravity CLI (if you don't have it) and sign in once:

curl -fsSL https://antigravity.google/cli/install.sh | bash
~/.local/bin/agy -p "ping" --print-timeout 5m   # opens a Google login the first time

2. Add the MCP server to Claude Code:

claude mcp add antigravity -- npx -y antigravity-claude-mcp

3. Check it's healthy (optional):

npx antigravity-claude-mcp doctor

4. Restart Claude Code, run /mcp to approve the tool, and ask:

"Use ask_antigravity to review my changes in src/auth.ts for edge cases."

How it works

┌────────────┐   MCP (stdio,    ┌─────────────────────────┐   agy -p     ┌──────────────────┐
│ Claude Code│   JSON-RPC 2.0)  │ antigravity-claude-mcp   │  --model …   │ Antigravity CLI  │
│  (Claude)  │ ───────────────▶ │  ask_antigravity tool    │ ───────────▶ │ Gemini 3 Pro /   │
│            │ ◀─────────────── │  (this package)          │ ◀─────────── │ Claude / GPT-OSS │
└────────────┘   tool result    └─────────────────────────┘   stdout     └──────────────────┘

The package is a tiny stdio MCP server that shells out to agy -p (Antigravity's headless print mode), optionally adding files/folders as context with --add-dir, and returns the model's text back to Claude.

The ask_antigravity tool

| Param | Type | Required | Description | |---------|------------|----------|-------------| | prompt| string | ✅ | The question, proposed approach, or review request. | | paths | string[] | | Absolute file/folder paths. Antigravity reads them in full as context. | | model | string | | Override the model (see below). Default: Gemini 3.1 Pro (High). |

Models

Whatever your Antigravity account exposes via agy models, for example:

• Gemini 3.1 Pro (High) ← default (strong, and a different family from Claude)
• Gemini 3.5 Flash (Low|Medium|High) (fast/cheap)
• Claude Sonnet 4.6 (Thinking), Claude Opus 4.6 (Thinking)
• GPT-OSS 120B (Medium)

Why default to Gemini, not Claude? The whole point is an independent reviewer. Using a Claude model to review Claude's work defeats the cross-check. Override per call with model if you want a specific one.

Configuration

Set as environment variables on the MCP server (e.g. via claude mcp add ... -e KEY=VAL):

| Variable | Default | Purpose | |---------------|-------------------------|---------| | AGY_BIN | auto-detected | Absolute path to the agy binary. | | AGY_MODEL | Gemini 3.1 Pro (High) | Default model for every call. | | AGY_TIMEOUT | 5m | Headless print timeout. |

Troubleshooting

agy runs but prints "passed to Electron/Chromium" warnings. You have the Antigravity IDE installed, and plain agy on your PATH is a symlink into Antigravity.app — that's the editor, not the CLI. This package auto-detects and skips it, preferring the real CLI at ~/.local/bin/agy. If you call agy by hand, use the full path or set AGY_BIN.

"Authentication required." Sign in once interactively: ~/.local/bin/agy -p "ping" --print-timeout 5m, open the printed Google link, approve, and paste the code back into that prompt.

Tool doesn't appear in Claude Code. Restart Claude Code after claude mcp add, then run /mcp and approve ask_antigravity. claude mcp list should show antigravity ✔ Connected.

vs. a proxy

Some projects route Claude Code's own traffic through Antigravity via an Anthropic-compatible proxy (i.e. Claude Code is "powered by" Antigravity). This is the opposite and complementary: Claude Code stays Claude, and Antigravity becomes a tool Claude can consult — so you get two genuinely different models in one loop instead of swapping one out for the other.

Requirements

• Claude Code CLI
• Antigravity CLI (agy), signed in
• Node.js ≥ 18

License

MIT © Arjun Thilak