Unity x Claude

Control the Unity Editor with natural language.
An MCP server that gives Claude 20 tools to create scripts, build scenes, modify components, manage assets, change settings, run builds, and execute C# — all from a conversation.

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Features

20 tools covering every part of the Unity Editor:

• Scene control — create, delete, duplicate, and inspect GameObjects. Read the full hierarchy with depth control, filter by tag or component.
• Component system — add, remove, read, and modify any component. Batch-update multiple properties in a single call. Wire object references between components.
• Script generation — create MonoBehaviours, ScriptableObjects, EditorWindows from templates. Modify existing scripts with find/replace, method injection, or full rewrites.
• Asset management — search by name or type, create Materials, Prefabs, ScriptableObjects, Folders. Import and re-import assets.
• Project settings — read and write Physics, Player, Quality, Audio, Time, Graphics, Input, Tags, Editor, and Navigation settings. All changes undoable.
• Build system — build for Windows, macOS, Linux, WebGL, Android, or iOS. Development builds, custom BuildOptions.
• Editor commands — play, pause, stop, step, save, undo, redo, compile, refresh. Run any Unity menu item.
• Live C# execution — run arbitrary C# inside the editor with full access to UnityEngine and UnityEditor APIs. Compiled in-memory — no temp files, no domain reload, instant results.

Built for performance:

• Zero CPU when idle — single background thread blocked on Socket.Poll. No async, no ThreadPool, no polling loops, no timers.
• Survives domain reloads — auto-restarts after script recompilation via [InitializeOnLoad]. 5-second safety net ensures the server is always running.
• Pure C# — no external dependencies, no DLLs, no NuGet packages. Just drop the folder into your project.

Built for safety:

• Everything is undoable — all destructive operations go through Unity's Undo system. Ctrl+Z works on every change Claude makes.
• Dangerous operations blocked — execute_csharp blocks Process.Start, Environment.Exit, Registry.*, and other unsafe calls.
• Port cleanup — server registers ProcessExit and DomainUnload handlers so the port is always released.

Built for testing:

• Runtime data during Play mode — component queries automatically include live position, rotation, velocity, and sleep state for physics objects.
• Screenshot verification — capture what the camera sees, describe visible objects with screen positions, simulate clicks on objects.
• Smart snapshots — schedule timed screenshots at animation keyframes to verify visual behavior with minimum captures.

Works with:

• Claude Desktop (via stdio bridge)
• Claude Code (direct HTTP)
• Cursor (direct HTTP)
• Any MCP-compatible client

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Installation

Step 1 — Add to your Unity project

Clone this repo (or download ZIP) and copy everything into your project's Packages folder:

YourProject/
  Packages/
    com.claude.unity-mcp/       ← put it here
      Editor/
      package.json
      mcp-bridge.mjs

Open Unity. The console should show:

[MCP] Ready on port 9999

Verify at Window > Claude MCP — shows server status, port, and all available tools.

Step 2 — Connect Claude

Open your Claude config file:

OS	Path
macOS	~/Library/Application Support/Claude/claude_desktop_config.json
Windows	%APPDATA%\Claude\claude_desktop_config.json

Add this (create the file if it doesn't exist):

{
  "mcpServers": {
    "unity": {
      "command": "node",
      "args": [
        "/full/path/to/YourProject/Packages/com.claude.unity-mcp/mcp-bridge.mjs"
      ]
    }
  }
}

Shortcut: In Unity, click Window > Claude MCP > Copy Config — it copies the JSON with the correct path. Just paste it into the file.

Using Claude Code or Cursor instead?

These support direct HTTP — no bridge needed:

{
  "mcpServers": {
    "unity": {
      "url": "http://localhost:9999/mcp"
    }
  }
}

Step 3 — Add the skill files

This is what makes Claude actually good at using the tools. Without these files, Claude can connect but won't know property paths, workarounds, batch patterns, or testing workflows.

Copy SKILL.md and WORKFLOW.md into Claude's skills folder:

# macOS / Linux
mkdir -p ~/.claude/skills/unity-x-claude
cp SKILL.md WORKFLOW.md ~/.claude/skills/unity-x-claude/

# Windows (PowerShell)
mkdir -Force "$env:USERPROFILE\.claude\skills\unity-x-claude"
copy SKILL.md, WORKFLOW.md "$env:USERPROFILE\.claude\skills\unity-x-claude\"

Using Claude Code or Cursor?

Put them in your project's .claude/skills/ folder instead:

mkdir -p YourProject/.claude/skills/unity-x-claude
cp SKILL.md WORKFLOW.md YourProject/.claude/skills/unity-x-claude/

What these files teach Claude:

File	What Claude learns
SKILL.md	All 20 tools with usage patterns, property paths for every common component (Transform, Rigidbody, Collider, Camera, Light, AudioSource), batch operation patterns, depth strategies, settings categories
WORKFLOW.md	Architecture, known gotchas with workarounds, runtime data inspection, screenshot testing pipeline, domain reload handling, port conflict recovery, safe C# execution patterns

Step 4 — Restart and test

Restart Claude Desktop (or start a new chat). Try:

• "What's in my Unity scene?"
• "Create a red cube at position 0, 3, 0 with a Rigidbody"
• "Change the gravity to -20 and set the quality level to Ultra"

If Claude responds with your scene data, you're done.

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Tool Reference

Category	Tools	Examples
Scene	get_scene, create_gameobject, delete, duplicate	Read hierarchy, spawn objects with components, clone objects
Components	get_components, set_property, add_component, remove_component	Inspect properties, batch-update 10+ values, wire references
Scripts	create_script, modify_script	Generate MonoBehaviours, find/replace in code, add methods
Assets	search_assets, get_asset, create_asset, import_asset	Find materials, create prefabs, re-import textures
Editor	editor_command, get_selection, set_selection, scene_view	Play/stop, save, undo, frame camera on object
Settings	get_settings, set_settings	Read/write Physics, Player, Quality, Audio, Time, Graphics
Build	build, manage_packages, get_console	Build for any platform, add packages, read errors
Code	execute_csharp	Run any C# with full Unity API access, in-memory compilation

All tools are prefixed with unity_ (e.g., unity_get_scene). See SKILL.md for the full reference with property paths and workflow patterns.

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Architecture

Claude Desktop / Claude Code / Cursor
        |
        | stdio (JSON-RPC 2.0)
        v
  mcp-bridge.mjs             Node.js — translates stdio ↔ HTTP
        |
        | HTTP POST localhost:9999/mcp
        v
  Unity Editor (MCPServer)
        |
        ├── StreamableHttpServer    Raw TcpListener, single thread, Socket.Poll
        ├── MainThreadDispatcher    ConcurrentQueue → EditorApplication.update
        ├── JsonRpcHandler          JSON-RPC 2.0 parsing
        ├── 8 Tool modules          Scene, Component, Asset, Script, Editor, Settings, Build, Execute
        └── Serialization           GameObject → JSON, Asset → JSON, Property helpers

Why zero CPU when idle

Component	Idle behavior
StreamableHttpServer	Thread blocked on Socket.Poll(1s) — true kernel wait, zero CPU
MainThreadDispatcher	ConcurrentQueue.TryDequeue returns false — single boolean check per frame
MCPServer.Tick()	One EditorApplication.update callback — nanosecond cost when empty
Status Window	No continuous repaint — updates only on interaction

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Compatibility

	Supported
Unity	2021.3 LTS and newer (tested on Unity 6.0)
Render Pipeline	URP, HDRP, Built-in
OS	macOS, Windows
MCP Clients	Claude Desktop, Claude Code, Cursor, or any MCP-compatible client
Node.js	Required for stdio bridge (Claude Desktop). Not needed for direct HTTP clients.

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Troubleshooting

Problem	Fix
Claude can't connect	Make sure Unity is open and Window > Claude MCP shows "Running"
Server not starting	Enable the toggle in Window > Claude MCP, or recompile (Ctrl+R)
Wrong project path	Use Window > Claude MCP > Copy Config to get the correct path
Node.js not found	Install Node.js — the bridge needs it: node --version
Port 9999 in use	Change port in Window > Claude MCP > Advanced Settings, update config to match
Calls fail after recompile	Normal — server restarts in 2-5 seconds. Just retry.

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Contributing

Pull requests welcome. If you add a new tool, follow the pattern in Editor/Tools/ and update SKILL.md with usage examples.

License

MIT