unity-mcp/Server
dsarno 8eb684ddc2
fix: comprehensive performance optimizations, claude code config, and stability improvements (issue #577) (#595)
* 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>
2026-01-20 18:11:25 -08:00
..
src fix: comprehensive performance optimizations, claude code config, and stability improvements (issue #577) (#595) 2026-01-20 18:11:25 -08:00
tests fix: parse and validate read_console types (#565) 2026-01-15 10:34:31 -08:00
DOCKER_OVERVIEW.md Publish to Docker Hub (#468) 2025-12-19 17:24:04 -04:00
Dockerfile HTTP Server, uvx, C# only custom tools (#375) 2025-11-24 23:21:06 -04:00
LICENSE Publish to pypi (#466) 2025-12-19 16:43:44 -04:00
README.md chore: bump version to 9.0.8 2026-01-19 14:07:05 +00:00
__init__.py Copy the MCP server to the top level (#354) 2025-10-25 00:53:53 -04:00
pyproject.toml fix: comprehensive performance optimizations, claude code config, and stability improvements (issue #577) (#595) 2026-01-20 18:11:25 -08:00
pyrightconfig.json Copy the MCP server to the top level (#354) 2025-10-25 00:53:53 -04:00
uv.lock feat: add test coverage tracking with pytest-cov (#512) 2026-01-08 17:32:44 -04:00

README.md

MCP for Unity Server

MCP python License Discord

Model Context Protocol server for Unity Editor integration. Control Unity through natural language using AI assistants like Claude, Cursor, and more.

Maintained by Coplay - This project is not affiliated with Unity Technologies.

💬 Join our community: Discord Server

Required: Install the Unity MCP Plugin to connect Unity Editor with this MCP server. You also need uvx (requires uv) to run the server.


Installation

Option 1: PyPI

Install and run directly from PyPI using uvx.

Run Server (HTTP):

uvx --from mcpforunityserver mcp-for-unity --transport http --http-url http://localhost:8080

MCP Client Configuration (HTTP):

{
  "mcpServers": {
    "UnityMCP": {
      "url": "http://localhost:8080/mcp"
    }
  }
}

MCP Client Configuration (stdio):

{
  "mcpServers": {
    "UnityMCP": {
      "command": "uvx",
      "args": [
        "--from",
        "mcpforunityserver",
        "mcp-for-unity",
        "--transport",
        "stdio"
      ]
    }
  }
}

Option 2: From GitHub Source

Use this to run the latest released version from the repository. Change the version to main to run the latest unreleased changes from the repository.

{
  "mcpServers": {
    "UnityMCP": {
      "command": "uvx",
      "args": [
        "--from",
        "git+https://github.com/CoplayDev/unity-mcp@v9.0.8#subdirectory=Server",
        "mcp-for-unity",
        "--transport",
        "stdio"
      ]
    }
  }
}

Option 3: Docker

Use Pre-built Image:

docker run -p 8080:8080 msanatan/mcp-for-unity-server:latest --transport http --http-url http://0.0.0.0:8080

Build Locally:

docker build -t unity-mcp-server .
docker run -p 8080:8080 unity-mcp-server --transport http --http-url http://0.0.0.0:8080

Configure your MCP client with "url": "http://localhost:8080/mcp".

Option 4: Local Development

For contributing or modifying the server code:

# Clone the repository
git clone https://github.com/CoplayDev/unity-mcp.git
cd unity-mcp/Server

# Run with uv
uv run src/main.py --transport stdio

Configuration

The server connects to Unity Editor automatically when both are running. No additional configuration needed.

Environment Variables:

  • DISABLE_TELEMETRY=true - Opt out of anonymous usage analytics
  • LOG_LEVEL=DEBUG - Enable detailed logging (default: INFO)

Example Prompts

Once connected, try these commands in your AI assistant:

  • "Create a 3D player controller with WASD movement"
  • "Add a rotating cube to the scene with a red material"
  • "Create a simple platformer level with obstacles"
  • "Generate a shader that creates a holographic effect"
  • "List all GameObjects in the current scene"

Documentation

For complete documentation, troubleshooting, and advanced usage:

📖 Full Documentation


Requirements

  • Python: 3.10 or newer
  • Unity Editor: 2021.3 LTS or newer
  • uv: Python package manager (Installation Guide)

License

MIT License - See LICENSE