Unity Ai Bridge MCP Server

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Unity AI Bridge

Remote-control the Unity Editor from any AI IDE — no ports, no dependencies, just works.

https://github.com/user-attachments/assets/4e8b3f85-b209-406f-a96e-f8b8eddc9160

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Why Unity AI Bridge?

Most AI coding assistants can read and write files, but they are blind to the Unity Editor — they can't inspect your scene, tweak materials, run tests, or profile performance. Unity AI Bridge gives AI full editor access.

Key Advantages

• 65 tools, 15 categories — Scene, GameObject, Assets, Prefab, Script, Profiler, LightProbe, Screenshot, Runtime, Tests, and more. Covers the full editor workflow, not just file I/O.
• File-based IPC, not WebSocket — No open ports, no firewall issues, no connection drops. Survives recompilation, play-mode transitions, and editor restarts gracefully.
• Zero external dependencies — Pure Python stdlib CLI/MCP server, self-contained C# Unity package. No pip install, no npm, no Node.js runtime.
• Every major AI IDE — Claude Code (Skill mode), Cursor, GitHub Copilot, Windsurf, Claude Desktop (MCP mode). One Unity plugin, all IDEs.
• 5-line extensibility — Add custom tools with [BridgeTool] attribute. Auto-discovered, auto-serialized, auto-documented. No registration code needed.
• Production-tested — Built for and battle-tested in a large-scale open-world Unity game (50+ developers, 2M+ lines of C#).

vs Unity 6 AI Gateway

Unity 6.2 introduced an official AI Gateway with MCP support. Both projects share the same goal — giving AI agents editor access via MCP — but differ in important ways:

In practice, the ~100ms file-polling latency is imperceptible because AI agent think-time dominates each round trip. File IPC also makes cross-process debugging trivial — just inspect the JSON files on disk.

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Quick Start

AI-native project — Copy the prompt below and send it to your AI coding assistant. The setup guide is written for AI to follow — you don't need to run any commands yourself.

Help me install Unity AI Bridge by following this guide:
https://github.com/butterlatte-zhang/unity-ai-bridge/blob/main/docs/SETUP.md

If you prefer manual setup:

1. Unity Package — In Unity: Window > Package Manager > + > Add package from git URL:

   https://github.com/butterlatte-zhang/unity-ai-bridge.git?path=Packages/com.aibridge.unity
   

   Or manually copy Packages/com.aibridge.unity from this repo into your project's Packages/ directory.

2. IDE Integration — Copy .claude/ to your project root, then configure your IDE per docs/SETUP.md.

Supports: Claude Code (Skill mode), Cursor, GitHub Copilot, Windsurf, Claude Desktop (MCP mode).

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Tool Categories

65 tools organized into 15 categories:

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Architecture

┌──────────────────────────────────────────────────┐
│                   AI IDE                         │
│  (Claude Code / Cursor / Copilot / Windsurf)     │
└──────────┬────────────────────┬──────────────────┘
           │                    │
     Skill mode            MCP mode
           │                    │
           ▼                    ▼
    ┌─────────────┐    ┌──────────────┐
    │  bridge.py  │    │ mcp_server.py│
    │  (Python)   │    │  (Python)    │
    └──────┬──────┘    └──────┬───────┘
           │                  │
           └────────┬─────────┘
                    │
              File-based IPC
            (request / response)
                    │
                    ▼
    ┌───────────────────────────────┐
    │     Unity Editor Plugin      │
    │   (com.aibridge.unity)       │
    │                              │
    │  BridgePlugin ← polls files  │
    │  BridgeToolRegistry          │
    │  BridgeToolRunner            │
    │  [BridgeTool] methods        │
    └───────────────────────────────┘

Dual-channel design: The same Unity plugin serves both Skill mode (direct CLI) and MCP mode (protocol server). Both channels communicate through the same file-based IPC — a pair of request/response files on disk. No network sockets, no port conflicts, no firewall rules.

Why file IPC? Unity's main thread is single-threaded and blocks during domain reload. File polling is the most reliable way to survive recompilation, play-mode transitions, and Editor restarts without losing messages.

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Beyond Editing — AI as Game Tester

Most Unity AI tools stop at file editing. Unity AI Bridge goes further — it turns Claude Code (or any AI IDE) into a game testing harness.

AI Playtest Loop

AI writes code → compiles → enters Play Mode → observes state → judges → fixes → repeats
     ↑                                                                         │
     └─────────────────── fully automated loop ────────────────────────────────┘

The pattern: Act → Wait → Observe → Judge → Repeat

• Act: runtime-invoke calls static methods to trigger game actions
• Wait: wait_playmode.py / wait_compile.py handle timing
• Observe: runtime-query reads MonoBehaviour fields + screenshot-capture for visuals
• Judge: AI analyzes state/screenshots to decide PASS/FAIL

Auto-Playtest Example | AI Closed-Loop Guide | Playtest Tool Reference

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Add Your Own Tools

Expose any static method to AI with a single attribute:

using UnityAiBridge;

[BridgeToolType]
public static partial class CustomTools
{
    [BridgeTool("custom-greet")]
    [System.ComponentModel.Description("Say hello")]
    public static string Greet(string name = "World")
    {
        return $"Hello, {name}!";
    }
}

The bridge discovers tools at Editor startup via reflection. No registration code, no config files. Parameters are automatically mapped to JSON Schema for the AI to call.

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Security

Unity AI Bridge runs entirely on your local machine. The file IPC channel is scoped to your user's temp directory, and no network listeners are opened.

See SECURITY.md for details.

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Compatibility

Platforms: Windows, macOS

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Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

• Report bugs and request features via GitHub Issues
• Submit pull requests against the main branch
• Add new tools by following the [BridgeTool] pattern above

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Acknowledgments

Unity AI Bridge is derived from Unity-MCP by Ivan Murzak (Apache License 2.0). See THIRD_PARTY_NOTICES.md for details.

License

Apache License 2.0