ULSM - Unity Language Server MCP

A Model Context Protocol (MCP) server providing Roslyn-based semantic code analysis for Unity 6.x projects. ULSM extends dotnet-roslyn-mcp with Unity-aware workspace loading, Unity-specific analyzers, and API migration checking.

22+ powerful tools including Unity diagnostics, pattern analysis, API migration checks, impact analysis, safe refactoring, and dependency visualization!

Why ULSM?

Unity projects have unique challenges that standard Roslyn tools don't handle well:

Challenge	ULSM Solution
Unity's legacy .csproj format (ToolsVersion 4.0)	Automatic MSBuild configuration
Absolute HintPath references to Unity DLLs	Framework path resolution + fallback parsing
Unity-specific anti-patterns (GetComponent in Update)	Microsoft.Unity.Analyzers + custom pattern detection
API deprecations in Unity 6.x	30+ migration rules with fix suggestions

Features

Standard Roslyn Capabilities

• Semantic Analysis: 100% compiler-accurate code understanding
• Cross-Solution Navigation: Find references, implementations, callers, and type hierarchies
• Impact Analysis: See what code calls your methods before refactoring
• Safe Refactoring: Rename symbols across solution with preview mode
• Dead Code Detection: Find unused types, methods, and fields
• Real-time Diagnostics: Get compilation errors and warnings

Unity-Specific Enhancements

• Unity Project Detection: Automatically detects Unity solutions by folder structure
• Unity Diagnostics: 50+ rules from Microsoft.Unity.Analyzers (UNT0001-UNT0xxx)
• Hot Path Analysis: Custom ULSM rules for GetComponent in Update, Camera.main, etc.
• API Migration: Check for deprecated Unity APIs with suggested replacements
• Legacy Format Support: Handles Unity's ToolsVersion 4.0 csproj files

Quick Start

Prerequisites

• .NET 8.0 SDK or Runtime
• (Optional) .NET Framework 4.7.1 Reference Assemblies (for full Unity DLL resolution)

Installation

# Install as global tool
dotnet tool install --global ulsm

# Verify installation
ulsm --version

Configure Claude Code

# Add ULSM to Claude Code
claude mcp add --transport stdio ulsm \
  --env DOTNET_SOLUTION_PATH="/path/to/YourUnityProject.sln" \
  -- ulsm

For Unity projects, you may also want to set the framework path:

claude mcp add --transport stdio ulsm \
  --env DOTNET_SOLUTION_PATH="/path/to/YourUnityProject.sln" \
  --env ULSM_FRAMEWORK_PATH="C:/Program Files (x86)/Reference Assemblies/Microsoft/Framework/.NETFramework/v4.7.1" \
  -- ulsm

Configuration

Environment Variables

Variable	Default	Description
DOTNET_SOLUTION_PATH	(Required)	Path to .sln file or directory containing it
ULSM_LOG_LEVEL	Information	Logging level (Debug, Information, Warning, Error)
ULSM_MAX_DIAGNOSTICS	100	Maximum diagnostics to return per request
ULSM_TIMEOUT_SECONDS	30	Operation timeout (increase for large solutions)
ULSM_FRAMEWORK_PATH	(Auto-detect)	Override path to .NET Framework 4.7.1 reference assemblies
ULSM_FORCE_ADHOC	false	Force AdhocWorkspace instead of MSBuildWorkspace
UNITY_EDITOR_PATH	(Auto-detect)	Path to Unity Editor installation for reference resolution

Path Resolution

DOTNET_SOLUTION_PATH supports three path formats:

Format	Example	Notes
Absolute	C:/Projects/MyGame/MyGame.sln	Always works reliably
Variable	${workspaceFolder}/MyGame.sln	Expanded by MCP client (recommended for portability)
Relative	./MyGame.sln	Resolved against process working directory

Recommended: Use ${workspaceFolder} in configuration files for portable, reliable path resolution:

{
  "env": {
    "DOTNET_SOLUTION_PATH": "${workspaceFolder}/MyGame.sln"
  }
}

Relative paths (e.g., ./MyGame.sln) work but are resolved against the MCP server's working directory, which may vary depending on how the server is launched.

Framework Path Locations

ULSM automatically searches for .NET Framework 4.7.1 reference assemblies:

Windows:

• C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.1
• C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.8

macOS:

• /Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.7.1-api

Linux:

• /usr/lib/mono/4.7.1-api

If these paths don't exist on your system, set ULSM_FRAMEWORK_PATH manually or install the .NET Framework Targeting Pack.

Available Tools (22 Total)

Core & Health

Tool	Description
ulsm:health_check	Check server health and workspace status (includes Unity detection info)
ulsm:load_solution	Load a .NET/Unity solution for analysis
ulsm:get_symbol_info	Get detailed semantic information about a symbol

Navigation

Tool	Description
ulsm:go_to_definition	Navigate to symbol definition
ulsm:find_references	Find all references to a symbol
ulsm:find_implementations	Find all implementations of an interface/abstract class
ulsm:find_callers	Find all methods that call a specific method (impact analysis)
ulsm:get_type_hierarchy	Get inheritance hierarchy for a type

Search

Tool	Description
ulsm:search_symbols	Search for symbols by name across solution
ulsm:semantic_query	Natural language semantic search

Diagnostics

Tool	Description
ulsm:get_diagnostics	Get compiler errors and warnings
ulsm:get_code_fixes	Get available code fixes for diagnostics
ulsm:apply_code_fix	Apply a specific code fix

Structure

Tool	Description
ulsm:get_project_structure	Get solution/project structure
ulsm:get_method_overloads	Get all overloads of a method
ulsm:get_containing_member	Get containing method/property/class info
ulsm:dependency_graph	Visualize project dependencies and detect cycles

Refactoring

Tool	Description
ulsm:organize_usings	Sort and remove unused using directives
ulsm:organize_usings_batch	Organize usings across multiple files
ulsm:format_document_batch	Format multiple documents
ulsm:rename_symbol	Safely rename symbol across solution with preview
ulsm:extract_interface	Generate interface from class for DI/testability

Analysis

Tool	Description
ulsm:find_unused_code	Find dead code (unused types, methods, fields)

Unity Analysis (New in ULSM)

Tool	Description
ulsm:unity_diagnostics	Get Unity-specific diagnostics (UNT0001, UNT0002, etc.)
ulsm:check_unity_patterns	Check for Unity anti-patterns (ULSM0001-0004)
ulsm:api_migration	Check for deprecated Unity APIs with migration suggestions
ulsm:list_unity_rules	List all available Unity diagnostic rules

Unity Diagnostics Reference

Microsoft.Unity.Analyzers (UNT Rules)

ID	Description	Severity
UNT0001	Empty Unity message (Update, Start, etc.)	Warning
UNT0002	Inefficient tag comparison (use CompareTag)	Warning
UNT0003	Usage of non-generic GetComponent	Info
UNT0006	Incorrect message signature	Error
UNT0010	MonoBehaviour instance created with new	Warning
UNT0014	Invalid method for GetComponent	Error
UNT0022	Unity objects should not use null coalescing	Warning
UNT0024	Prefer float math over double	Info

[Full list available via ulsm:list_unity_rules]

ULSM Custom Patterns (ULSM Rules)

ID	Description	Severity
ULSM0001	Expensive call in hot path (GetComponent in Update)	Warning
ULSM0002	String operation in hot path (allocation)	Warning
ULSM0003	Debug.Log in hot path (performance)	Info
ULSM0004	Camera.main in hot path (expensive property)	Warning

API Migration Categories

Category	Example Deprecations
Input	Input.GetAxis -> Input System
Networking	NetworkBehaviour -> Netcode for GameObjects
Rendering	Camera.stereoActiveEye -> XR APIs
XR	XRSettings -> XR Management
Physics	Various query method updates

Example Prompts

Unity-Specific Analysis

"Check my PlayerController for Unity anti-patterns"
"What Unity APIs in my project are deprecated in Unity 6?"
"Find all GetComponent calls in Update methods"
"List all Unity diagnostics in the Assembly-CSharp project"

Impact Analysis

"Find all callers of the ProcessInput method"
"What code will break if I change this method signature?"
"Who uses the PlayerStats class?"

Safe Refactoring

"Preview renaming IWeaponHandler to IWeapon"
"Safely rename ProcessInput to HandleInput across the solution"

Dead Code Detection

"Find all unused code in the Scripts folder"
"What private methods are never called?"
"Show me unused ScriptableObjects"

Architecture

+-------------------------------------------------+
|         Claude Code (MCP Client)                |
+------------------------+------------------------+
                         | stdin/stdout (JSON-RPC 2.0)
+------------------------v------------------------+
|              McpServer.cs                       |
|  - Protocol handling                            |
|  - Tool registration (22+ tools)                |
|  - Request routing                              |
+------------------------+------------------------+
                         |
+------------------------v------------------------+
|            RoslynService.cs                     |
|  - Solution management                          |
|  - Semantic analysis                            |
|  - Symbol resolution                            |
|  - Unity project detection                      |
+------------------------+------------------------+
                         |
          +--------------+--------------+
          |                             |
+---------v---------+   +---------------v-----------------------+
| MSBuildWork-      |   |    Unity/                             |
| space             |   |  +- UnityProjectDetector              |
| (Standard)        |   |  +- UnityWorkspaceLoader              |
|                   |   |  +- UnityAnalysisService              |
|                   |   |  +- Analyzers/                        |
|                   |   |      +- UnityAnalyzerLoader           |
|                   |   |      +- UnityPatternAnalyzer          |
|                   |   |      +- UnityApiMigrationData         |
+-------------------+   +---------------------------------------+

Troubleshooting

Unity Project Not Detected

Symptom: Health check shows isUnityProject: false for a Unity project.

Causes and Solutions:

1. No Assembly-CSharp.csproj: Regenerate project files in Unity (Edit -> Preferences -> External Tools -> Regenerate Project Files)

2. Missing folder structure: ULSM looks for Assets/ and ProjectSettings/ folders

3. Path resolution issues: If using relative paths, ensure they resolve correctly. Use ${workspaceFolder}/YourProject.sln for reliable resolution, or use absolute paths

Framework Reference Errors

Symptom: Many CS0012 errors about missing types like System.Object.

Solution: Set ULSM_FRAMEWORK_PATH to your .NET Framework 4.7.1 reference assemblies:

# Windows
ULSM_FRAMEWORK_PATH="C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.7.1"

# macOS (with Mono)
ULSM_FRAMEWORK_PATH="/Library/Frameworks/Mono.framework/Versions/Current/lib/mono/4.7.1-api"

MSBuild Workspace Failures

Symptom: Solution fails to load with MSBuild errors.

Solution: Try forcing AdhocWorkspace mode:

ULSM_FORCE_ADHOC=true

This bypasses MSBuild and parses .csproj files directly. You may lose some features but gain compatibility.

Large Solution Timeout

Symptom: Loading times out for large Unity projects.

Solution: Increase the timeout:

ULSM_TIMEOUT_SECONDS=120

Unity Analyzers Not Loading

Symptom: ulsm:list_unity_rules returns empty or ulsm:unity_diagnostics finds nothing.

Solution: Ensure the solution is loaded first:

1. Call ulsm:load_solution if not auto-loaded
2. Check ulsm:health_check shows "Ready" status
3. Verify unityAnalyzersLoaded: true in health check response

Building from Source

# Clone the repository
git clone https://github.com/prespective/ulsm.git
cd ulsm

# Build
dotnet build ULSM.sln -c Release

# Run tests
dotnet test ULSM.sln

# Pack as global tool
dotnet pack src/ULSM.csproj -c Release

# Install locally
dotnet tool install --global --add-source ./src/bin/Release ulsm

Running from Source (Development)

claude mcp add --transport stdio ulsm-dev \
  --env DOTNET_SOLUTION_PATH="/path/to/YourUnityProject.sln" \
  -- dotnet run --project /path/to/ulsm/src/ULSM.csproj

MCP Client Configuration Examples

Claude Code (Recommended)

~/.claude/mcp_servers.json:

{
  "servers": {
    "ulsm": {
      "command": "ulsm",
      "args": [],
      "env": {
        "DOTNET_SOLUTION_PATH": "C:/Projects/MyUnityGame/MyUnityGame.sln",
        "ULSM_FRAMEWORK_PATH": "C:/Program Files (x86)/Reference Assemblies/Microsoft/Framework/.NETFramework/v4.7.1",
        "ULSM_LOG_LEVEL": "Information"
      }
    }
  }
}

Project-Local Configuration

.claude/mcp-spec.json (in your Unity project root):

{
  "mcpServers": {
    "ulsm": {
      "command": "ulsm",
      "env": {
        "DOTNET_SOLUTION_PATH": "${workspaceFolder}/MyGame.sln"
      }
    }
  }
}

VS Code (with MCP extension)

.vscode/settings.json:

{
  "mcp.servers": {
    "ulsm": {
      "command": "ulsm",
      "env": {
        "DOTNET_SOLUTION_PATH": "${workspaceFolder}/MyGame.sln"
      }
    }
  }
}

Contributing

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

Development Setup

1. Fork and clone the repository
2. Open ULSM.sln in your IDE
3. Run tests: dotnet test
4. Make changes
5. Submit a pull request

Credits

ULSM is a fork of dotnet-roslyn-mcp by Brendan Kowitz, extended with Unity-specific capabilities by Prespective.

Key Dependencies

• Microsoft.CodeAnalysis (Roslyn) - Compiler APIs
• Microsoft.Unity.Analyzers - Unity-specific diagnostics
• ModelContextProtocol - MCP SDK

License

MIT License - See LICENSE for details.

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Built with Roslyn for Unity developers who want AI-powered code assistance that truly understands their codebase.