antigravity-cli-mcp

A minimal MCP server that exposes Antigravity CLI (agy) as a single tool callable from Claude Code (or any MCP client). This wraps the terminal CLI, not the Antigravity IDE; you need agy installed and signed in.

This project started as gemini-cli-mcp, wrapping Gemini CLI. Gemini CLI is deprecated in favor of Antigravity, so the server now spawns agy instead. The tool interface is the same shape; see Migrating from gemini-cli-mcp.

How it works

Claude Code sends prompts to this server via MCP. The server spawns agy -p "..." in headless mode and returns the response. Antigravity inherits your Google sign-in, so no API key is required.

Claude Code ──MCP/stdio──▶ antigravity-cli-mcp ──spawn──▶ agy -p "..." --output-format json --add-dir <cwd>

Prerequisites

• Antigravity CLI installed, on your PATH as agy, and signed in (run agy once interactively to complete login). Requires a version with headless JSON output (1.1.8 or later; tested against 1.2.7).

Installation

From source

git clone https://github.com/danwahl/antigravity-cli-mcp
cd antigravity-cli-mcp
npm install
npm run build

Configuration

User install (available across all projects):

claude mcp add antigravity -s user -- npx -y @danwahl/antigravity-cli-mcp

Project install (shared with your team via .mcp.json):

claude mcp add antigravity -s project -- npx -y @danwahl/antigravity-cli-mcp

Or from source, replace npx -y @danwahl/antigravity-cli-mcp with node /absolute/path/to/antigravity-cli-mcp/dist/index.js.

Verify with claude mcp list.

Tool: cli

| Parameter | Type | Required | Description | |------------------|---------|----------|-------------| | prompt | string | yes | Task or question to send to Antigravity | | cwd | string | yes | Absolute path to the working directory (agy's workspace) | | model | string | no | Model name, e.g. gemini-3.1-pro-high, gemini-3.8-flash-medium, claude-sonnet-4-6. Omit for agy's default. agy models lists the options. | | effort | string | no | Reasoning effort: low, medium, or high. Omit for agy's default. | | sandbox | boolean | no | Default true. Shell commands can read anywhere but write only under /tmp; agy's file edit tools are unaffected. Set false for builds, installs, git commits, or tests that write to the workspace. | | mode | string | no | plan or accept-edits. In headless mode plan review is auto-approved, so plan shapes the workflow but does not block edits. | | agent | string | no | Custom agent name, defined at .agents/agents/<name>.md in the workspace or ~/.gemini/config/agents/. | | jsonSchema | object | no | JSON Schema enforced on the final answer. The parsed object comes back in structuredOutput. | | conversationId | string | no | Resume a previous conversation. Returned in the structured output of each call. Pass the same cwd, since conversations are workspace-scoped. | | timeout | number | no | Seconds before the run is stopped. Default 120. On expiry the call returns an error; any partial response is in the structured output. |

Structured output

Each call returns structured content alongside the text response:

{
  "conversationId": "dc381a74-...",
  "response": "Antigravity's answer...",
  "status": "SUCCESS",
  "usage": {
    "inputTokens": 12447,
    "outputTokens": 122,
    "thinkingTokens": 121,
    "cacheReadTokens": 0,
    "totalTokens": 12569
  },
  "structuredOutput": null,
  "durationSeconds": 2.6,
  "numTurns": 1,
  "deniedActions": []
}

agy's JSON output does not include per-tool call counts or a per-model breakdown, so those fields from the Gemini CLI version are gone.

What Antigravity can do

agy runs with --dangerously-skip-permissions, giving it full tool access: read/write files, run shell commands, web search, and more. Headless agy cannot prompt for permission, so without this flag any tool needing approval is silently denied and the turn ends early. Deny rules in agy's own settings.json still apply; when one fires the call returns an error listing deniedActions.

The cwd you specify is passed as --add-dir so it becomes the agent's workspace; the spawn working directory alone is not enough in headless mode.

--sandbox is on by default as a check against the permission bypass. It restricts shell commands only: they can read anywhere but write only under /tmp. agy's file edit tools can still modify the workspace.

Timeouts and cancellation

The timeout is passed to agy as --print-timeout, so agy stops its own turn at the deadline and returns whatever it has. The server reports that as an error with the partial response in the structured output. If agy fails to exit within a few seconds after that, its process group is killed. Cancelling the MCP call (for example, interrupting Claude Code) kills the agy process group immediately.

Errors

On a model or API failure agy prints an AGY_ERROR: {...} line to stderr and exits with code 3. The server surfaces the status and message from that line as the tool error.

Migrating from gemini-cli-mcp

• sessionId is now conversationId (both the input parameter and the output field).
• models and tools in the structured output are replaced by a single usage object.
• Gemini CLI model aliases (auto, pro, flash, flash-lite) are not recognized; use a name from agy models.
• Re-add the server under the new package name: claude mcp remove gemini-cli then the claude mcp add command above.

Development

npm run build   # compile with tsc
npm test        # run unit tests

Smoke test

echo '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}' | node dist/index.js

Design

One tool, no prompt wrappers. Claude Code is the orchestrator: it decides what to ask Antigravity and how to phrase it. This server is a thin, reliable pipe between MCP and agy -p.

See CLAUDE.md for project conventions.