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Summer Engine in Antigravity

Antigravity is Google’s AI-powered IDE that supports MCP (Model Context Protocol). With Summer Engine’s integration, Antigravity’s AI can control your game engine: add nodes to scenes, set properties, import assets, run the game, and debug, all from within your coding workflow. This guide covers the configuration. Setup takes about a minute.

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Prerequisites

  • Antigravity: Google’s AI-powered IDE or the agy CLI
  • Node.js: For running the MCP server (Node 18+)
  • Summer Engine: Installed and running with your project open

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Configuration

This writes the summer-engine server into ~/.gemini/config/mcp_config.json, the file the Antigravity IDE, the Antigravity CLI (agy) and Antigravity 2.0 share, installs the skill library to ~/.gemini/config/skills/, and runs summer doctor. Add --scope project to write .agents/mcp_config.json and .agents/skills/ in the project instead.
Coming from Gemini CLI? Gemini CLI was retired for individual accounts on 2026-06-18 and Antigravity replaced it. The Summer Gemini extension still works for Workspace and enterprise Gemini CLI users (summer setup gemini), but new setups should use Antigravity.

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Option 2: Manual configuration

Antigravity uses the mcpServers shape. The files are:
  • User-level: ~/.gemini/config/mcp_config.json
  • Project-level: .agents/mcp_config.json in the project root

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Step 1: Create or Edit the Config File

Create the file if it doesn’t exist. If it already has other MCP servers, add Summer Engine to the existing mcpServers object.

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Step 2: Add Summer Engine

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Step 3: Reload MCP servers

In the agent panel open the MCP servers view and refresh, or restart Antigravity. The Summer Engine MCP server starts when Antigravity starts; it connects to the engine on the first tool call.

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Step 4: Verify

Check Antigravity’s MCP or AI settings to confirm “summer-engine” appears and its tools are listed. Then try a prompt:
  • “Use Summer Engine to add a MeshInstance3D with a BoxMesh to the scene”
If the node appears in Summer Engine, the setup is working.

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Using Summer Engine with Antigravity

Once configured, the AI can use Summer Engine’s tools when you ask for game-related changes. Example prompts:
  • “Add a Camera3D and DirectionalLight3D to the scene root”
  • “Get the scene tree from Summer Engine”
  • “Import this model and add it to the World node: [URL]”
  • “Run the game and capture a screenshot”
  • “Set the project’s main scene to res://main.tscn”
Engine must be running. Antigravity’s AI talks to Summer Engine over localhost. Open your project in the engine first, or run npx summer-engine run from the project directory.

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Troubleshooting

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”Summer Engine is not running”

Start Summer Engine and open your project. The MCP server connects to the engine’s local API on port 6550. The engine writes a token to ~/.summer/api-token when it starts.

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MCP server not appearing

  • Config path: Verify ~/.gemini/config/mcp_config.json (user) or .agents/mcp_config.json in the project root. .vscode/mcp.json from older guides is VS Code’s file, not Antigravity’s.
  • JSON validity: Ensure no trailing commas, proper quotes, and valid JSON structure
  • Restart: Fully quit and reopen Antigravity

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Tools return errors

See the Tools Reference for parameter formats. Common issues: wrong node path format (./World/Player), invalid property values (use engine string format like "Vector3(0, 10, 0)"), or the game running when scene edits are attempted (stop it first with summer_stop).

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Next Steps

Tools Reference

Every MCP tool with parameters and examples

Building a Game

How an AI builds a full game using MCP

MCP Setup Overview

Architecture, prerequisites, and other IDEs

CLI Reference

summer install, run, create, and more
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