> ## Documentation Index
> Fetch the complete documentation index at: https://docs.summerengine.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Build Games in Codex with Summer Engine MCP

> Connect Summer Engine's MCP server to Codex and build games with OpenAI's AI coding assistant driving your engine.

## Summer Engine in Codex

Codex is OpenAI's AI coding assistant that supports MCP (Model Context Protocol). With Summer Engine's integration, Codex 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

* **Codex**: OpenAI's AI coding assistant (CLI or IDE extension)
* **Node.js**: For running the MCP server (Node 18+)
* **Summer Engine**: Installed and running with your project open

## Configuration

Codex uses TOML configuration. The config file is:

* **User-level:** `~/.codex/config.toml` (applies to all projects)
* **Project-level:** `.codex/config.toml` in your project root (trusted projects only)

You can configure via the CLI or by editing the config file directly.

### Option 1: CLI (Recommended)

Add Summer Engine with a single command:

```bash theme={null}
codex mcp add summer-engine -- npx summer-engine mcp
```

### Option 2: Edit config.toml

Create or edit `~/.codex/config.toml` and add:

<CodeGroup>
  ```toml New file (~/.codex/config.toml) theme={null}
  [mcp_servers.summer-engine]
  command = "npx"
  args = ["summer-engine", "mcp"]
  ```

  ```toml Adding to existing config theme={null}
  [mcp_servers.other-server]
  command = "npx"
  args = ["-y", "@some/other-mcp"]

  [mcp_servers.summer-engine]
  command = "npx"
  args = ["summer-engine", "mcp"]
  ```
</CodeGroup>

In the Codex IDE extension, you can open the config via **MCP settings** > **Open config.toml** from the gear menu.

### Step 3: Restart Codex

Close and reopen Codex (or the IDE extension) so it loads the new MCP config. The Summer Engine MCP server starts when Codex starts; it connects to the engine on the first tool call.

### Step 4: Verify

In the Codex TUI, use `/mcp` to see your active MCP servers. You should see "summer-engine" with 52 tools. 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 Codex

Once configured, Codex 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.** Codex 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 `~/.codex/config.toml` exists (or `.codex/config.toml` for project scope)
* **TOML syntax:** Ensure valid TOML (no trailing commas, proper section headers)
* **Restart:** Fully quit and reopen Codex

### 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">
    All 23 MCP tools 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.