* fix: reduce per-frame GC allocations causing editor hitches (issue #577) Eliminate memory allocations that occurred every frame, which triggered garbage collection spikes (~28ms) approximately every second. Changes: - EditorStateCache: Skip BuildSnapshot() entirely when state unchanged (check BEFORE building). Increased poll interval from 0.25s to 1.0s. Cache DeepClone() results to avoid allocations on GetSnapshot(). - TransportCommandDispatcher: Early exit before lock/list allocation when Pending.Count == 0, eliminating per-frame allocations when idle. - StdioBridgeHost: Same early exit pattern for commandQueue. - MCPForUnityEditorWindow: Throttle OnEditorUpdate to 2-second intervals instead of every frame, preventing expensive socket checks 60+/sec. Fixes GitHub issue #577: High performance impact even when MCP server is off * fix: prevent multiple domain reloads when calling refresh_unity (issue #577) Root Cause: - send_command() had a hardcoded retry loop (min 6 attempts) on connection errors - Each retry resent the refresh_unity command, causing Unity to reload 6 times - retry_on_reload=False only controlled reload-state retries, not connection retries The Fix: 1. Unity C# (MCPForUnity/Editor): - Added --reinstall flag to uvx commands in dev mode - Ensures local development changes are picked up by uvx/Claude Code - Applies to all client configurators (Claude Code, Codex, etc.) 2. Python Server (Server/src): - Added max_attempts parameter to send_command() - Pass max_attempts=0 when retry_on_reload=False - Fixed type handling in refresh_unity.py (handle MCPResponse objects) - Added timeout to connection error recovery conditions - Recovery logic now returns success instead of error to prevent client retries Changes: - MCPForUnity/Editor: Added --reinstall to dev mode uvx commands - Server/refresh_unity.py: Fixed type handling, improved error recovery - Server/unity_connection.py: Added max_attempts param, disable retries when retry_on_reload=False Result: refresh_unity with compile=request now triggers only 1 domain reload instead of 6 Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com> * fix: UI and server stability improvements Unity Editor (C#): - Fix "Resuming..." stuck state when manually clicking End Session Clear ResumeStdioAfterReload and ResumeHttpAfterReload flags in OnConnectionToggleClicked and EndOrphanedSessionAsync to prevent UI from getting stuck showing "Resuming..." with disabled button - Remove unsupported --reinstall flag from all uvx command builders uvx does not support --reinstall and shows warning when used Use --no-cache --refresh instead for dev mode cache busting Python Server: - Add "aborted" to connection error patterns in refresh_unity Handle WinError 10053 (connection aborted) gracefully during Unity domain reload, treating it as expected behavior - Add WindowsSafeRotatingFileHandler to suppress log rotation errors Windows file locking prevents log rotation when file is open by another process; catch PermissionError to avoid noisy stack traces - Fix packaging: add py-modules = ["main"] to pyproject.toml setuptools.packages.find only discovers packages (directories with __init__.py), must explicitly list standalone module files Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com> * docs: improve refresh_unity connection loss handling documentation Add detailed comments and logging to clarify why connection loss during compile is treated as success (expected domain reload behavior, not failure). This addresses PR feedback about potentially masking real connection errors. The logic is intentional and correct: - Connection loss only treated as success when compile='request' - Domain reload causing disconnect is expected Unity behavior - Subsequent wait_for_ready loop validates Unity becomes ready - Prevents multiple domain reload loops (issue #577) Added logging for observability: - Info log when expected disconnect detected - Warning log for non-recoverable errors Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com> * fix: add missing logger import in refresh_unity Missing logger import causes NameError at runtime when connection loss handling paths are triggered (lines 82 and 91). Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com> * fix: address code review feedback on thread safety and semantics Addresses four issues raised in code review: 1. EditorStateCache.GetSnapshot() - Remove shared cached clone - Revert to always returning fresh DeepClone() to prevent mutation bugs - Main GC optimization remains: state-change detection prevents unnecessary _cached rebuilds (the expensive operation) - Removed _cachedClone and _cachedCloneSequence fields 2. refresh_unity.py - Fix blocking reason terminology mismatch - Changed "asset_refresh" to "asset_import" to match activityPhase values from EditorStateCache.cs - Ensures asset import is correctly detected as blocking state 3. TransportCommandDispatcher - Fix unsynchronized Count access - Moved Pending.Count check inside PendingLock - Prevents data races and InvalidOperationException from concurrent dictionary access 4. StdioBridgeHost - Fix unsynchronized Count access - Moved commandQueue.Count check inside lockObj - Ensures all collection access is properly serialized All changes maintain the GC allocation optimizations while fixing thread safety violations and semantic contract changes. Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com> * fix: address code review feedback on thread safety and timeout handling - refresh_unity.py: Track readiness explicitly and return failure on timeout instead of silently returning success when wait loop exits without confirming ready_for_tools=true - McpClientConfiguratorBase.cs: Add thread safety guard for Configure() call in CheckStatusWithProjectDir(). Changed default attemptAutoRewrite to false and added runtime check to prevent calling Configure() from background threads. Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> --------- Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com> |
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| .claude | ||
| .github | ||
| CustomTools/RoslynRuntimeCompilation | ||
| MCPForUnity | ||
| Server | ||
| TestProjects | ||
| docs | ||
| scripts | ||
| tools | ||
| .dockerignore | ||
| .gitignore | ||
| LICENSE | ||
| README-zh.md | ||
| README.md | ||
| claude_skill_unity.zip | ||
| deploy-dev.bat | ||
| docker-compose.yml | ||
| mcp_source.py | ||
| prune_tool_results.py | ||
| restore-dev.bat | ||
| test_unity_socket_framing.py | ||
README.md
| English | 简体中文 |
|---|
Proudly sponsored and maintained by Coplay -- the best AI assistant for Unity.
Create your Unity apps with LLMs! MCP for Unity bridges AI assistants (Claude, Cursor, VS Code, etc.) with your Unity Editor via the Model Context Protocol. Give your LLM tools to manage assets, control scenes, edit scripts, and automate tasks.
Quick Start
Prerequisites
- Unity 2021.3 LTS+ — Download Unity
- Python 3.10+ and uv — Install uv
- An MCP Client — Claude Desktop | Cursor | VS Code Copilot | Windsurf
1. Install the Unity Package
In Unity: Window > Package Manager > + > Add package from git URL...
[!TIP]
https://github.com/CoplayDev/unity-mcp.git?path=/MCPForUnity
Need a stable/fixed version? Use a tagged URL (requires uninstall to update):
https://github.com/CoplayDev/unity-mcp.git?path=/MCPForUnity#v9.0.3
Other install options (Asset Store, OpenUPM)
Unity Asset Store:
- Visit MCP for Unity on the Asset Store
- Click
Add to My Assets, then import viaWindow > Package Manager
OpenUPM:
openupm add com.coplaydev.unity-mcp
2. Start the Server & Connect
- In Unity:
Window > MCP for Unity - Click Start Server (launches HTTP server on
localhost:8080) - Select your MCP Client from the dropdown and click Configure
- Look for 🟢 "Connected ✓"
- Connect your client: Some clients (Cursor, Windsurf, Antigravity) require enabling an MCP toggle in settings, while others (Claude Desktop, Claude Code) auto-connect after configuration.
That's it! Try a prompt like: "Create a red, blue and yellow cube" or "Build a simple player controller"
Features & Tools
Key Features
- Natural Language Control — Instruct your LLM to perform Unity tasks
- Powerful Tools — Manage assets, scenes, materials, scripts, and editor functions
- Automation — Automate repetitive Unity workflows
- Extensible — Works with various MCP Clients
Available Tools
manage_asset • manage_editor • manage_gameobject • manage_components • manage_material • manage_prefabs • manage_scene • manage_script • manage_scriptable_object • manage_shader • manage_vfx • batch_execute • find_gameobjects • find_in_file • read_console • refresh_unity • run_tests • get_test_job • execute_menu_item • apply_text_edits • script_apply_edits • validate_script • create_script • delete_script • get_sha
Available Resources
custom_tools • unity_instances • menu_items • get_tests • gameobject • gameobject_components • editor_state • editor_selection • editor_prefab_stage • project_info • project_tags • project_layers
Performance Tip: Use batch_execute for multiple operations — it's 10-100x faster than individual calls!
Manual Configuration
If auto-setup doesn't work, add this to your MCP client's config file:
HTTP (default — works with Claude Desktop, Cursor, Windsurf):
{
"mcpServers": {
"unityMCP": {
"url": "http://localhost:8080/mcp"
}
}
}
VS Code:
{
"servers": {
"unityMCP": {
"type": "http",
"url": "http://localhost:8080/mcp"
}
}
}
Stdio configuration (legacy)
macOS/Linux:
{
"mcpServers": {
"unityMCP": {
"command": "uv",
"args": ["run", "--directory", "/Users/YOUR_USERNAME/Library/AppSupport/UnityMCP/UnityMcpServer/src", "server.py", "--transport", "stdio"]
}
}
}
Windows:
{
"mcpServers": {
"unityMCP": {
"command": "C:/Users/YOUR_USERNAME/AppData/Local/Microsoft/WinGet/Links/uv.exe",
"args": ["run", "--directory", "C:/Users/YOUR_USERNAME/AppData/Local/UnityMCP/UnityMcpServer/src", "server.py", "--transport", "stdio"]
}
}
}
Multiple Unity Instances
MCP for Unity supports multiple Unity Editor instances. To target a specific one:
- Ask your LLM to check the
unity_instancesresource - Use
set_active_instancewith theName@hash(e.g.,MyProject@abc123) - All subsequent tools route to that instance
Roslyn Script Validation (Advanced)
For Strict validation that catches undefined namespaces, types, and methods:
- Install NuGetForUnity
Window > NuGet Package Manager→ InstallMicrosoft.CodeAnalysisv4.14.0- Also install
SQLitePCLRaw.coreandSQLitePCLRaw.bundle_e_sqlite3 - Add
USE_ROSLYNtoPlayer Settings > Scripting Define Symbols - Restart Unity
Manual DLL installation (if NuGetForUnity isn't available)
- Download
Microsoft.CodeAnalysis.CSharp.dlland dependencies from NuGet - Place DLLs in
Assets/Plugins/folder - Ensure .NET compatibility settings are correct
- Add
USE_ROSLYNto Scripting Define Symbols - Restart Unity
Troubleshooting
- Unity Bridge Not Connecting: Check
Window > MCP for Unitystatus, restart Unity - Server Not Starting: Verify
uv --versionworks, check the terminal for errors - Client Not Connecting: Ensure the HTTP server is running and the URL matches your config
Detailed setup guides:
- Fix Unity MCP and Cursor, VSCode & Windsurf — uv/Python installation, PATH issues
- Fix Unity MCP and Claude Code — Claude CLI installation
- Common Setup Problems — macOS dyld errors, FAQ
Still stuck? Open an Issue or Join Discord
Contributing
See README-DEV.md for development setup. For custom tools, see CUSTOM_TOOLS.md.
- Fork → Create issue → Branch (
feature/your-idea) → Make changes → PR
Telemetry & Privacy
Anonymous, privacy-focused telemetry (no code, no project names, no personal data). Opt out with DISABLE_TELEMETRY=true. See TELEMETRY.md.
License: MIT — See LICENSE | Need help? Discord | Issues
Star History
Unity AI Tools by Coplay
Coplay offers 3 AI tools for Unity:
- MCP for Unity is available freely under the MIT license.
- Coplay is a premium Unity AI assistant that sits within Unity and is more than the MCP for Unity.
- Coplay MCP a free-for-now MCP for Coplay tools.
(These tools have different tech stacks. See this blog post comparing Coplay to MCP for Unity.)
Disclaimer
This project is a free and open-source tool for the Unity Editor, and is not affiliated with Unity Technologies.