Unity C# LSP Plugin for Claude Code

A Language Server Protocol (LSP) plugin for Claude Code, optimized for Unity game development with C#.

Features

• Go to Definition - Jump to symbol definitions across your Unity project
• Find References - Locate all usages of classes, methods, and variables
• Hover Information - View type signatures and documentation
• Document Symbols - Navigate file structure quickly
• Diagnostics - Real-time error and warning detection
• Unity-Optimized - Configured for Unity's Mono runtime and project structure
• Cross-Platform - Works on Windows, macOS, and Linux
• Auto-Installation - Automatically detects and installs OmniSharp if missing

Requirements

• Claude Code v2.0.74 or later
• .NET SDK 6.0+ - Download here
• Unity Project with generated .sln and .csproj files
• Windows: Visual Studio 2022 (any edition) - required for MSBuild

Installation

Method A: Install from GitHub (Recommended)

The easiest way to install - just two commands:

# Add the plugin marketplace
claude plugin marketplace add bruno1308/unity-csharp-lsp-claude-code

# Install the plugin (loads automatically in all projects)
claude plugin install unity-csharp-lsp --scope user

Restart Claude Code and the plugin will load automatically. No --plugin-dir flag needed!

Method B: Manual Installation

If you prefer to install manually or need to modify the plugin:

Step 1: Clone the repository

git clone https://github.com/bruno1308/unity-csharp-lsp-claude-code.git
cd unity-csharp-lsp-claude-code

Step 2: Copy to plugins directory

Windows (PowerShell):

$dest = Join-Path $env:USERPROFILE ".claude\plugins\unity-csharp-lsp"
New-Item -ItemType Directory -Force -Path $dest
Copy-Item -Path ".\*" -Destination $dest -Recurse -Force

macOS / Linux:

mkdir -p ~/.claude/plugins/unity-csharp-lsp
cp -r ./* ~/.claude/plugins/unity-csharp-lsp/

Step 3: Restart Claude Code

Close and reopen Claude Code for the plugin to load.

Step 4: Verify installation

Run /plugins in Claude Code and check that unity-csharp-lsp appears in the list.

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OmniSharp Setup

The plugin requires OmniSharp to be installed on your system. The plugin will attempt to auto-install on first run, but you can also install manually:

Windows

# Option 1: Install via Scoop (Recommended)
scoop install omnisharp

# Option 2: Install via winget
winget install OmniSharp.OmniSharp

# Option 3: Download from GitHub releases
# https://github.com/OmniSharp/omnisharp-roslyn/releases
# Extract and add to PATH

macOS

# Install OmniSharp with Mono support (Required for Unity)
brew tap omnisharp/omnisharp-roslyn
brew install omnisharp-mono

Important: Use omnisharp-mono (not just omnisharp) for Unity projects to ensure Mono runtime compatibility.

Linux

# Option 1: Download from GitHub releases
# https://github.com/OmniSharp/omnisharp-roslyn/releases
# Download the linux-x64 or linux-arm64 version, extract, and add to PATH

# Option 2: Build from source
# See: https://github.com/OmniSharp/omnisharp-roslyn#building

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Unity Project Setup

For the LSP to work, your Unity project needs valid solution and project files.

Generate project files

1. Open your Unity project in the Unity Editor
2. Go to Edit > Preferences > External Tools
3. Under "Generate .csproj files for:", check the boxes for your needs
4. Click Regenerate project files
5. Verify that .sln and Assembly-CSharp.csproj files exist in your project root

Optional: Add OmniSharp configuration

Create an omnisharp.json file in your Unity project root for custom settings:

{
  "msbuild": {
    "enabled": true,
    "UseLegacySdkResolver": true
  },
  "formattingOptions": {
    "enableEditorConfigSupport": true,
    "useTabs": false,
    "tabSize": 4
  },
  "roslynExtensionsOptions": {
    "enableAnalyzersSupport": true,
    "enableImportCompletion": true
  }
}

Important: The UseLegacySdkResolver: true setting helps with SDK resolution on systems with multiple .NET SDK versions.

A sample configuration file is included: omnisharp.json.sample

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Supported File Types

Extension	Language	LSP Support
.cs	C#	Full
.csx	C# Script	Full

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Troubleshooting

"No LSP server available for file type"

1. Verify OmniSharp is installed and in your PATH:

   omnisharp --version
   # or
   OmniSharp --version

2. Restart Claude Code after installing OmniSharp
3. Check /plugins > Errors tab for details

Plugin not loading after restart

If using Method C (/plugin install), try Method A (copy to ~/.claude/plugins/) instead.

LSP not finding Unity types

1. Ensure your Unity project has a valid .sln file
2. Regenerate project files in Unity Editor
3. Check that Assembly-CSharp.csproj exists

macOS: OmniSharp crashes with Unity projects

Use the Mono version instead of the .NET version:

brew install omnisharp-mono  # NOT just 'omnisharp'

Large projects: Slow initial load

OmniSharp needs to index your project on first load. This can take 60-90 seconds for large Unity projects with many assemblies. Subsequent loads will be faster.

Windows: "SDK WorkloadAutoImportPropsLocator could not be found"

This error occurs when there's a mismatch between your .NET SDK version and Visual Studio's MSBuild. The plugin includes a workaround (MSBuildEnableWorkloadResolver=false) that should handle this automatically.

If you still see this error:

1. Ensure you have .NET SDK 6.0+ installed: dotnet --list-sdks
2. Verify Visual Studio 2022 is installed (provides MSBuild)
3. Check that omnisharp.json in your Unity project has "UseLegacySdkResolver": true

LSP returns empty results (0 symbols, 0 references)

This usually means projects failed to load. Check:

1. Wait 60-90 seconds after starting Claude Code for indexing
2. Verify your Unity project has a valid .sln file
3. Check /plugins > Errors for SDK-related errors
4. Try regenerating project files in Unity Editor

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How it works

This plugin configures Claude Code to use OmniSharp as the Language Server for C# files. When you open a Unity project:

1. Claude Code detects .cs files
2. The plugin starts OmniSharp with Unity-optimized settings
3. OmniSharp indexes your project using the .sln file
4. Claude gains access to semantic code intelligence

LSP Operations Available

Operation	Status	What Claude can do
documentSymbol	✅ Works	List all symbols (classes, methods, fields) in a file
workspaceSymbol	✅ Works	Search for symbols across the entire workspace
hover	✅ Works	Get type information and documentation
goToDefinition	✅ Works	Navigate to where symbols are defined
findReferences	✅ Works	Find all usages of a class, method, or variable
goToImplementation	✅ Works	Find implementations of interfaces/abstract classes
getDiagnostics	✅ Works	See compiler errors and warnings
prepareCallHierarchy	❌ N/A	Not supported by OmniSharp
incomingCalls	❌ N/A	Not supported by OmniSharp
outgoingCalls	❌ N/A	Not supported by OmniSharp

Performance

• Navigation queries: ~50ms (vs ~45 seconds with text search)
• Reference lookups: Near-instant across entire codebase
• Real-time diagnostics: Errors shown as you discuss code

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Plugin Structure

unity-csharp-lsp/
├── .claude-plugin/
│   └── plugin.json          # Plugin metadata
├── .lsp.json                 # OmniSharp configuration
├── hooks/
│   ├── hooks.json            # Auto-install hooks
│   ├── check-omnisharp.sh    # macOS/Linux installer
│   └── check-omnisharp.ps1   # Windows installer
├── omnisharp.json.sample     # Sample project config
├── CLAUDE.md                 # Instructions for Claude
├── README.md                 # This file
└── LICENSE                   # MIT License

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Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Test with a Unity project
4. Commit your changes (git commit -m 'Add amazing feature')
5. Push to the branch (git push origin feature/amazing-feature)
6. Open a Pull Request

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License

MIT License - see LICENSE file for details.

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Acknowledgments

• OmniSharp - The C# language server
• Claude Code - Anthropic's CLI coding assistant
• Piebald-AI/claude-code-lsps - LSP plugin reference