Antigravity

Antigravity is Google's agentic IDE. Its MCP config lives in the GLOBAL file ~/.gemini/config/mcp_config.json, shared with the Gemini CLI.

Manual setup only

cairn does NOT auto-write Antigravity's config. Its exact config path and local/stdio schema aren't yet confirmed from official docs, so cairn shows this guide instead of writing the file. On the Connect page, Antigravity carries a Manual badge and has no button.

Add the cairn entry yourself:

{
  "mcpServers": {
    "cairn": {
      "command": "/absolute/path/to/bin/cairn",
      "args": ["serve", "--actor", "agent:antigravity", "--repo", "/absolute/path/to/project"]
    }
  }
}

command is the absolute path to your built cairn binary (use your bin/cairn absolute path), and --repo is this project's absolute path.

Open the file via Antigravity → Manage MCP Servers → View raw config, paste the cairn entry, and save. Antigravity reloads automatically.

Identity

Antigravity connects as agent:antigravity by default. Edit the --actor value to run multiple instances (e.g. agent:antigravity-2). See Sessions for how identity is enforced.

Gotchas

• Antigravity shares config with the Gemini CLI. The mcpServers shape is confirmed, but the exact file path (~/.gemini/config/mcp_config.json) comes from a single source, so verify against your install.
• Antigravity uses serverUrl for REMOTE servers, but cairn is a LOCAL stdio server, so it uses command/args as shown.