Roslyn MCP Server

A robust, TypeScript-based Model Context Protocol (MCP) server integration for the official Microsoft Roslyn Language Server (C#).

This standalone tool connects the Model Context Protocol with the C# Language Server Protocol (LSP), allowing AI agents—such as Claude Desktop, Cursor, and other MCP-compatible clients—to semantically understand, navigate, and analyze your C# and .NET codebases just like a native IDE.

Features

• Full C# LSP Coverage: Exposes core semantic tools including advanced hover documentation, definition seeking, project-wide references, and diagnostic build errors.
• High Stability: Internally manages didOpen document synchronization and handles LSP buffer states automatically, preventing the NullReferenceException bugs occasionally seen in other LSP wrappers.
• Zero Configuration: Installs seamlessly and falls back to tracking your Current Working Directory dynamically if you don't enforce an absolute project path.

Global Installation

npm install -g roslyn-mcp-server

Pre-requisites

You must have the .NET 8 SDK (or above) installed along with the official roslyn-language-server dotnet tool.

dotnet tool install -g Microsoft.CodeAnalysis.LanguageServer

How to Configure in MCP Clients

Add the following to your MCP Host configurations (e.g., claude_desktop_config.json, mcp_config.json, etc.):

{
  "mcpServers": {
    "csharp-lsp": {
      "command": "roslyn-mcp-server",
      "args": ["<OPTIONAL_ABSOLUTE_PATH_TO_CSHARP_PROJECT>"]
    }
  }
}

Tip: If you do not provide <OPTIONAL_ABSOLUTE_PATH_TO_CSHARP_PROJECT> in args, the server will gracefully fallback and index the Current Working Directory (CWD).

Exposed MCP Tools

• csharp_hover: Fetches the semantic type or variable definitions in markdown formatting precisely at line/column boundaries.
• csharp_definition: Retrieves the concrete origination URI of the symbol.
• csharp_references: Locates all occurrences or assignments of methods/properties across the entire initialized workspace.
• csharp_diagnostics: Summarizes the active syntax errors and build warnings on a targeted component.
• csharp_workspace_symbol: Queries fuzzy name references broadly across large infrastructures without needing to know exact paths.

Local Development

1. Run npm install to gather dependencies.
2. Run npm run build to compile the TypeScript payload into dist/.
3. Use npm start to execute the production payload, or use the provided src/test.ts to perform end-to-end local debugging simulating an MCP client.