> ## Documentation Index
> Fetch the complete documentation index at: https://summer-18f03259-codex-native-multiplayer-entry.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Build Games in Antigravity with Summer Engine MCP

> Connect Summer Engine's MCP server to Antigravity and build games with Google's AI-powered IDE driving your engine.

## 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.

## 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

## Configuration

### Option 1: One-command setup (recommended)

```bash theme={null}
npx -y summer-engine@latest setup antigravity --yes
```

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.

<Note>
  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.
</Note>

### 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

#### 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.

#### Step 2: Add Summer Engine

<CodeGroup>
  ```json New file (~/.gemini/config/mcp_config.json) theme={null}
  {
    "mcpServers": {
      "summer-engine": {
        "command": "npx",
        "args": ["-y", "summer-engine@latest", "mcp"]
      }
    }
  }
  ```

  ```json Adding to existing mcpServers theme={null}
  {
    "mcpServers": {
      "other-server": { ... },
      "summer-engine": {
        "command": "npx",
        "args": ["-y", "summer-engine@latest", "mcp"]
      }
    }
  }
  ```
</CodeGroup>

### 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.

### 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.

## 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"

<Tip>
  **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.
</Tip>

## Troubleshooting

### "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.

### 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

### Tools return errors

See the [Tools Reference](/mcp/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`).

## Next Steps

<CardGroup cols={2}>
  <Card title="Tools Reference" icon="wrench" href="/mcp/tools-reference">
    Every MCP tool with parameters and examples
  </Card>

  <Card title="Building a Game" icon="gamepad-2" href="/mcp/building-a-game">
    How an AI builds a full game using MCP
  </Card>

  <Card title="MCP Setup Overview" icon="plug" href="/mcp/setup">
    Architecture, prerequisites, and other IDEs
  </Card>

  <Card title="CLI Reference" icon="terminal" href="/mcp/cli-reference">
    summer install, run, create, and more
  </Card>
</CardGroup>

***

Need help or have questions? Reach out to our founders at [founders@summerengine.com](mailto:founders@summerengine.com) or join our community on [Discord](https://discord.gg/yUpgtxnZky) for fast responses.