Roslyn MCP Server

Let AI assistants like Claude safely refactor your C# codebase using the same Roslyn compiler platform that powers Visual Studio.

Roslyn MCP Server is a Model Context Protocol (MCP) server that exposes 41 Roslyn-powered tools to AI assistants and other MCP clients. It combines 19 refactoring operations, 5 code navigation tools, 6 analysis and metrics tools, 4 code generation tools, and 7 code conversion tools -- giving your AI deep code intelligence, comprehensive refactoring, and modern C# syntax transformations with full solution-wide reference tracking and preview support.

Why RoslynMcpServer?
Prerequisites
Quick Start
Standalone CLI
Configuration
Available Tools
Preview Mode
Troubleshooting
NuGet Libraries
Contributing
License

Why RoslynMcpServer?

41 tools -- refactoring, navigation, analysis, generation, and conversion tools, the most comprehensive Roslyn MCP server available
Preview mode on every operation -- see exactly what will change before applying
Atomic file writes with rollback -- if any file write fails, all changes are reverted
Solution-wide reference updates -- renames and moves propagate across your entire solution
Single command install -- dotnet tool install -g RoslynMcp.Server, no repo cloning needed
Cross-platform -- works on Windows, Linux, and macOS

Prerequisites

Before installing, make sure you have:

.NET 9.0 SDK or later -- Download here
A C# solution (.sln or .slnx) or project (.csproj) to work with

Verify your .NET SDK version:

dotnet --version

The output should be 9.0.x or higher.

Quick Start

1. Install

dotnet tool install -g RoslynMcp.Server

2. Configure

Create a .mcp.json file in your project root (for Claude Code):

{
  "mcpServers": {
    "roslyn-refactor": {
      "type": "stdio",
      "command": "roslyn-mcp",
      "args": []
    }
  }
}

Then restart Claude Code or run /mcp to connect.

3. Verify

Ask Claude:

"Run the roslyn diagnose tool for my solution at C:/path/to/MySolution.sln"

You should see a health report with Roslyn version, MSBuild status, and workspace details.

4. Try It

Ask Claude:

"Rename the class UserService to AccountService in C:/path/to/MySolution.sln"

Claude will use the rename_symbol tool to rename the class and update every reference across your entire solution.

Standalone CLI

All 41 tools are also available as a standalone CLI for use in scripts, CI/CD pipelines, and terminals without an AI assistant.

Install

dotnet tool install -g RoslynMcp.Cli

Usage

roslyn-cli <solution-path> <tool-name> [--option value ...]
roslyn-cli <tool-name> --help
roslyn-cli --help

Examples

# Check environment health
roslyn-cli C:/path/to/MySolution.sln diagnose --format text

# Rename a symbol across the entire solution
roslyn-cli C:/path/to/MySolution.sln rename-symbol --source-file C:/path/to/Foo.cs --symbol-name Bar --new-name Baz

# Get compiler diagnostics (errors only), pipe to jq
roslyn-cli C:/path/to/MySolution.sln get-diagnostics --severity-filter Error | jq '.data'

# Preview a refactoring without applying
roslyn-cli C:/path/to/MySolution.sln extract-method --source-file Foo.cs --start-line 10 --end-line 20 --method-name DoWork --preview

Output is JSON by default (pipeable to jq). Use --format text for human-readable output. Exit codes: 0=success, 1=tool error, 2=CLI error, 3=environment error.

Configuration

Claude Code

Create .mcp.json in your project root:

{
  "mcpServers": {
    "roslyn-refactor": {
      "type": "stdio",
      "command": "roslyn-mcp",
      "args": []
    }
  }
}

Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "roslyn-refactor": {
      "command": "roslyn-mcp",
      "args": []
    }
  }
}

Config file locations:

| OS | Path | |---------|-------------------------------------------------------------| | Windows | %APPDATA%\Claude\claude_desktop_config.json | | macOS | ~/Library/Application Support/Claude/claude_desktop_config.json |

Available Tools

All tools accept a solutionPath parameter (absolute path to a .sln, .slnx, or .csproj file). Refactoring tools also accept a preview parameter (set to true to see changes without applying them).

Move and Rename

| Tool | Description | Key Parameters | |------|-------------|----------------| | move_type_to_file | Move a C# type declaration to a different file. Updates all references automatically. | sourceFile, symbolName, targetFile, createTargetFile | | move_type_to_namespace | Change the namespace of a C# type. Updates all using directives and qualified references. | sourceFile, symbolName, targetNamespace, updateFileLocation | | rename_symbol | Rename any C# symbol (type, method, property, field, variable, etc.) with automatic reference updates across the solution. | sourceFile, symbolName, newName, line, column, renameOverloads, renameFile |

Extract

| Tool | Description | Key Parameters | |------|-------------|----------------| | extract_method | Extract selected code into a new method. Automatically detects parameters and return values. | sourceFile, startLine, startColumn, endLine, endColumn, methodName, visibility | | extract_variable | Extract an expression to a local variable. | sourceFile, startLine, startColumn, endLine, endColumn, variableName, useVar | | extract_constant | Extract a literal value to a named constant. | sourceFile, startLine, startColumn, endLine, endColumn, constantName, visibility, replaceAll | | extract_interface | Extract an interface from a class's public members. | sourceFile, typeName, interfaceName, members, targetFile | | extract_base_class | Extract members to a new base class. | sourceFile, typeName, baseClassName, members, targetFile, makeAbstract |

Inline

| Tool | Description | Key Parameters | |------|-------------|----------------| | inline_variable | Inline a local variable by replacing all usages with its initializer value. | sourceFile, variableName, line |

Signature and Encapsulation

| Tool | Description | Key Parameters | |------|-------------|----------------| | change_signature | Add, remove, or reorder method parameters and update all call sites. | sourceFile, methodName, parameters (array of changes), line | | encapsulate_field | Convert a field to a property with backing field. | sourceFile, fieldName, propertyName, readOnly |

Generate

| Tool | Description | Key Parameters | |------|-------------|----------------| | generate_constructor | Generate a constructor that initializes fields and/or properties of a type. | sourceFile, typeName, members, addNullChecks | | generate_overrides | Generate override methods for base class virtual/abstract members. | sourceFile, typeName, members, callBase | | implement_interface | Generate interface member implementations for a type. | sourceFile, typeName, interfaceName, explicitImplementation, members |

Convert

| Tool | Description | Key Parameters | |------|-------------|----------------| | convert_to_async | Convert a synchronous method to async/await pattern. | sourceFile, methodName, line, renameToAsync | | convert_expression_body | Toggle between expression body (=> expr;) and block body ({ return expr; }). | sourceFile, direction, memberName, line | | convert_property | Convert between auto-property and full property with backing field. | sourceFile, direction, propertyName, line | | convert_foreach_linq | Convert foreach loops with Add patterns to LINQ Select/Where expressions. | sourceFile, line | | convert_to_pattern_matching | Convert if/is chains and switch statements to switch expressions. | sourceFile, line | | convert_to_interpolated_string | Convert string.Format() calls and concatenation to interpolated strings. | sourceFile, line | | introduce_parameter | Promote a local variable to a method parameter, updating all call sites. | sourceFile, variableName, line |

Using Directives

| Tool | Description | Key Parameters | |------|-------------|----------------| | add_missing_usings | Add missing using directives required to resolve unbound type references. Process a single file or all files in the solution. | sourceFile, allFiles | | remove_unused_usings | Remove unused using directives. Process a single file or all files in the solution. | sourceFile, allFiles | | sort_usings | Sort using directives alphabetically in a C# file. | sourceFile

RoslynMcpServer

Install / Use

README