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_find_dead_code`	Find potentially dead types, methods, and fields across the active workspace, with optional inclusion of public APIs
`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

Build the solution in Release mode
Install the generated .vsix from src/RoslynMcpExtension/bin/Release/
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/mcp"
    }
  }
}

VS Code (GitHub Copilot)

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

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

Any MCP Client

Use Streamable HTTP with http://localhost:5050/mcp for GitHub Copilot and modern MCP clients.

This server is intentionally configured in stateless HTTP mode so reconnects remain reliable across server restarts and solution changes. Legacy SSE endpoints are not required for the Roslyn tools and are not used by the recommended GitHub Copilot setup.

Dead Code Analysis

roslyn_find_dead_code reports potentially unused methods, fields, and types from the live Visual Studio workspace. It uses Roslyn semantic references plus additional heuristics for framework-driven and runtime-driven code paths that do not always appear as normal source references.

The analysis is intentionally conservative and already filters several common false-positive patterns:

Test code: xUnit, NUnit, and MSTest attributes such as Fact, Theory, Test, TestCase, TestMethod, DataTestMethod, setup/cleanup attributes, and types that contain or inherit test methods
Interface contracts: both explicit and implicit interface implementations
XAML usage: event handlers, code-behind types, and parameterless constructors for controls and windows instantiated from .xaml
Visual Studio / MEF composition: Export, Import, ImportingConstructor, and Visual Studio package types decorated with PackageRegistrationAttribute
Generated and interop code: common generated files, compiler-generated members, and marshaling / StructLayout fields
Extension patterns: static extension containers, classic this extension methods, and newer C# extension(...) { } blocks

Dead-code detection can never be perfect, especially for reflection-heavy or externally activated code, so results should still be reviewed before deletion.

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

Find dead code in the active workspace and list unused methods, fields, and types

Find dead code in the active workspace and include public members as well

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