Roslyn MCP Extension — Visual Studio Extension

A Visual Studio extension that exposes semantic C# code analysis via the Model Context Protocol (MCP), powered by the live Roslyn workspace inside Visual Studio.

Unlike standalone Roslyn MCP servers that create their own MSBuildWorkspace, this extension uses Visual Studio's actual VisualStudioWorkspace — giving you access to unsaved changes, live diagnostics, and the full compilation state that VS already maintains.

MCP Tools

| Tool | Description | |------|-------------| | roslyn_validate_file | Get live diagnostics (errors, warnings, analyzer results) for a C# file | | roslyn_find_references | Semantic find-all-references using SymbolFinder (not text search) | | roslyn_go_to_definition | Navigate to symbol definition via Roslyn semantic model | | roslyn_get_document_symbols | List all symbols in a file with types, modifiers, and spans | | roslyn_search_symbols | Search for symbol declarations across the solution by name | | roslyn_get_symbol_info | Get detailed type information, base types, interfaces, parameters |

Prerequisites

• Visual Studio 2022 or 2026
• .NET 10.0 SDK (for the server process)

Building

The solution file is at src/RoslynMcpExtension.slnx. Since the VSIX project requires MSBuild, build via Visual Studio or msbuild:

# Full solution (requires Visual Studio / MSBuild)
msbuild src\RoslynMcpExtension.slnx

# Server and Shared projects only (dotnet CLI)
dotnet build src\RoslynMcpExtension.Server\RoslynMcpExtension.Server.csproj

The VSIX project automatically publishes the MCP server process to its output directory.

Installation

1. Build the solution in Release mode
2. Install the generated .vsix from src/RoslynMcpExtension/bin/Release/
3. Restart Visual Studio

Usage

Starting the Server

The server auto-starts when a solution is loaded (configurable in Tools > Options > Roslyn MCP Extension).

You can also manually start/stop via Tools > Start/Stop Roslyn MCP Server.

Configuration

In Tools > Options > Roslyn MCP Server:

• Port: HTTP port (default: 5050)
• Server Name: Name shown to MCP clients
• Auto Start: Start automatically when a solution loads

Connecting MCP Clients

Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "roslyn-mcp": {
      "url": "http://localhost:5050/sse"
    }
  }
}

VS Code (GitHub Copilot)

Add to your .vscode/mcp.json or user settings:

{
  "servers": {
    "roslyn-mcp": {
      "url": "http://localhost:5050/sse"
    }
  }
}

Any MCP Client

Connect to http://localhost:5050/sse using HTTP/SSE transport.

Example Prompts

Validate the file C:\MyProject\src\UserService.cs for errors and warnings

Find all references to the method ProcessOrder in C:\MyProject\src\OrderService.cs at line 42, column 20

Search for all symbols named "Repository" in the current solution

How It Differs from Other Roslyn MCP Servers

| Feature | This Extension | Others roslyn/mcp servers | |---------|---------------|---------------------------------------| | Workspace | Live VS VisualStudioWorkspace | Standalone MSBuildWorkspace | | Unsaved changes | ✅ Sees current editor state | ❌ Only saved files | | Find References | ✅ Semantic SymbolFinder | ❌ Text search or separate workspace | | Diagnostics | ✅ Live from VS compiler | ⚠️ Re-compiled separately | | Build integration | ✅ Uses VS compilation state | ❌ Separate compilation | | Setup | Install VSIX, no config needed | Configure solution path per project |

License

MIT