Unity MCP Server

MCP server for the Unity Editor. Lets AI agents like Claude Code inspect, manipulate, test, and screenshot your project.

Highlights

• 73 tools: scenes, GameObjects, components, prefabs, transforms, tests, reflection + decompilation, C# eval, UI capture

• Zero-config clients: one click (or one command) per machine, then every project and editor connects automatically. No ports, no tokens, no per-project config

• Multi-editor safe: each open project runs its own server, sessions route to the right one by themselves

• MCP resources: console logs, scene hierarchy, test results, project files

• Unity 2022.3+ (Unity 6 recommended), Node.js 18+

Install

Package Manager > + > Add package from git URL:

https://github.com/Singtaa/UnityMCP.git

Or clone / submodule into Packages/com.singtaa.unity-mcp.

Setup (once per machine)

1. Open the project in Unity. Server auto-starts, launcher deploys to ~/.unity-mcp/stdio.js

2. Window > Unity MCP Server > Set up Claude Code

Done. Terminal equivalent:

# macOS / Linux
claude mcp add --scope user --transport stdio unity -- node ~/.unity-mcp/stdio.js

# Windows
claude mcp add --scope user --transport stdio unity -- node "%USERPROFILE%\.unity-mcp\stdio.js"

Every Claude Code session inside any Unity project now reaches that project's own editor. Multiple editors side by side: each session finds its own. Editor closed or mid-reload: tools return a clear error and recover on their own. Opening the editor mid-session works too: a session started editor-closed registers the tool list immediately (served from a per-project cache) and re-syncs live the moment the editor comes up, no client restart needed.

Under the hood: the editor writes a per-session beacon (Temp/UnityMcp_Endpoint.json, removed on quit, never stale). The launcher resolves the session's project (CLAUDE_PROJECT_DIR, else cwd walk-up, UNITY_MCP_PROJECT overrides both) and proxies MCP to that project's live endpoint, re-reading the beacon on every request. It declares tools.listChanged and watches the beacon: when an editor appears (or a different one takes over the project), it emits list_changed notifications so clients re-fetch the tool and resource lists mid-session. Launcher deployment to ~/.unity-mcp/stdio.js is upgrade-only by LAUNCHER_VERSION, so editors on different package versions never fight over the file.

Other MCP clients: same launcher, or plain HTTP (endpoint + token shown in the window).

Tools

Notable:

• unity_eval: compile + run a C# snippet in the editor, no domain reload. Expression form returns its value, statement form uses return. Common usings imported, leading using lines hoisted. Bundled Roslyn (C# 9 ceiling). First call warms up for a few seconds, then tens of ms per compile

• unity_capture_panel: renders a UI Toolkit PanelSettings to PNG offscreen, no scene chrome, works in edit and play mode. Auto-detects the active UIDocument

• unity_assets_find: Project-window query syntax (t:Material, t:Prefab ui, l:MyLabel), optional folder scoping, capped results with total count

• unity_reflection_decompile: full C# source of any loaded type or method

• Quirks: wait ~1s after a domain reload before test tools; unity_capture_game_view is play-mode-only on Unity 6.3+

Resources

unity://console/logs · unity://hierarchy · unity://hierarchy/{scene} · unity://tests/results · unity://project/files

Configuration

ProjectSettings/McpSettings.json (meant to be committed): HTTP port 5173, IPC port 52100, auto-start, auth token.

Ports taken by another project's server? A free pair is auto-allocated and stored per-machine in UserSettings/McpPortOverride.json (gitignored), so port shuffles never reach the team. Project identity is validated on every bridge connection: an editor can never adopt another project's server, even with misconfigured ports.

Manual server start: node src/server.js with MCP_PROJECT_ROOT set to the project path.

Works with Unity CLI

Complementary, not competing:

• Unity CLI owns editor lifecycle: installs, unity open, builds, CI

• UnityMCP owns the live editor session: UI capture, decompilation, eval, test loops, zero-config routing

• Typical agent loop: unity open <project> via CLI, editor boots, server + beacon come up, launcher connects. No config on either side

• CLI-launched editors run unfocused / in the background. UnityMCP is built and tested for exactly that (background-safe startup, retry through domain reloads)

• No port or tool-name conflicts. Register both

Architecture

┌─────────────────────────────────────────────────────────────┐
│                      AI Assistant                           │
├──────────────────────────────┬──────────────────────────────┤
│  stdio launcher              │  (or direct HTTP clients)    │
│  ~/.unity-mcp/stdio.js       │                              │
│  resolves the session's      │                              │
│  project, reads its beacon   │                              │
│  Temp/UnityMcp_Endpoint.json │                              │
├──────────────────────────────┴──────────────────────────────┤
│           HTTP JSON-RPC (Port 5173, per project)            │
├─────────────────────────────────────────────────────────────┤
│              Node.js MCP Server (Server~/)                  │
├─────────────────────────────────────────────────────────────┤
│                TCP NDJSON (Port 52100)                      │
├─────────────────────────────────────────────────────────────┤
│                Unity Editor C# Bridge                       │
│  (McpBridge → ToolRegistry → MainThreadDispatcher)          │
├─────────────────────────────────────────────────────────────┤
│                     Unity APIs                              │
└─────────────────────────────────────────────────────────────┘

Each open project runs its own Node server. The launcher is the shared front door that routes every session to the right one.

Development

• Unity tests: Window > General > Test Runner (EditMode + PlayMode)

• Launcher tests: npm test in Server~/

• Changelog: CHANGELOG.md

License

MIT. See LICENSE.