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?

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`

Diagnostics

Tool	Description	Key Parameters
`diagnose`	Check the health of the Roslyn MCP server environment and workspace status.	`solutionPath` (optional), `verbose`

Code Navigation

These read-only tools let you explore and understand your codebase without making changes. Use them to discover symbols, trace references, and inspect type information before refactoring.

Tool	Description	Key Parameters
`find_references`	Find all references to a symbol across the entire solution. Returns file locations, context snippets, and write/definition indicators.	`sourceFile`, `symbolName`, `line`, `column`, `maxResults`
`go_to_definition`	Navigate to the source definition of a symbol. Supports partial classes with multiple definition locations.	`sourceFile`, `symbolName`, `line`, `column`
`get_symbol_info`	Get detailed metadata for any symbol: kind, accessibility, modifiers, base types, interfaces, members, parameters, return type, and XML documentation.	`sourceFile`, `symbolName`, `line`, `column`
`find_implementations`	Find all implementations of an interface or overrides of an abstract/virtual member.	`sourceFile`, `symbolName`, `line`, `column`, `maxResults`
`search_symbols`	Search for symbols by name pattern across the entire workspace. Filter by kind (class, method, property, etc.).	`query`, `kindFilter`, `maxResults`

Analysis & Metrics

These tools analyze your code without making changes. Use them to understand code quality, data flow, and control flow.

Tool	Description	Key Parameters
`get_diagnostics`	Retrieve compiler diagnostics (errors, warnings, info) filtered by severity and optionally by file.	`sourceFile`, `severityFilter`
`get_code_metrics`	Calculate code metrics: cyclomatic complexity, lines of code, maintainability index, class coupling, depth of inheritance.	`sourceFile`, `symbolName`, `line`
`analyze_control_flow`	Analyze control flow for a code region: start/end point reachability, return statements, and exit points.	`sourceFile`, `startLine`, `endLine`
`analyze_data_flow`	Analyze data flow for a code region: variables read/written inside, data flowing in/out, captured variables.	`sourceFile`, `startLine`, `endLine`
`find_callers`	Find all callers of a symbol across the entire solution.	`sourceFile`, `symbolName`, `line`, `column`, `maxResults`
`get_type_hierarchy`	Retrieve the type hierarchy (base types and/or derived types) for a given type.	`sourceFile`, `symbolName`, `line`, `column`, `direction`
`get_document_outline`	Get a hierarchical outline of all symbols in a file (namespaces, types, members).	`sourceFile`

Code Generation

These tools generate new code members for existing types.

Tool	Description	Key Parameters
`generate_equals_hashcode`	Generate Equals() and GetHashCode() overrides for a type based on its fields/properties.	`sourceFile`, `typeName`, `fields`
`generate_tostring`	Generate a ToString() override for a type.	`sourceFile`, `typeName`, `fields`, `format`
`format_document`	Format a C# file using Roslyn's built-in formatter.	`sourceFile`
`add_null_checks`	Add null-check statements (ArgumentNullException.ThrowIfNull or guard clauses) for method parameters.	`sourceFile`, `methodName`, `line`, `style`

Preview Mode

Every refactoring tool supports a preview parameter. When set to true, the tool computes and returns the changes that would be made without writing anything to disk. This lets you review diffs before committing to a refactoring.

Example (as a natural language prompt to Claude):

"Preview what would happen if I renamed OrderProcessor to OrderHandler in C:/path/to/MySolution.sln"

Claude will call rename_symbol with preview: true and show you the affected files and diffs.

Troubleshooting

.NET 9 SDK not found

If you see errors about the SDK not being found:

Verify the SDK is installed: dotnet --list-sdks
Make sure .NET 9.0 or later appears in the list
If not, install it from https://dotnet.microsoft.com/download/dotnet/9.0

MSBuild or solution loading issues

If MSBuild cannot be located or your solution fails to load:

Make sure you can build the solution from the command line first: dotnet build /path/to/MySolution.sln
On Windows, ensure Visual Studio Build Tools or a Visual Studio installation is available
Check that solutionPath is an absolute path to a valid .sln, .slnx, or .csproj file

Using the diagnose tool

The diagnose tool is the first thing to try when something is not working. It reports:

Whether Roslyn is loaded and its version
Whether MSBuild was found and its version
Whether the .NET SDK is available and its version
Whether a given solution can be loaded, including project and document counts

Run it through Claude:

"Run the roslyn diagnose tool with verbose output for C:/path/to/MySolution.sln"

Or without a solution path to check just the environment:

"Run the roslyn diagnose tool"

NuGet Libraries

In addition to the global tool, the project publishes libraries for building custom integrations:

# Core library -- refactoring operations and workspace management
dotnet add package RoslynMcp.Core

# Contracts library -- shared models and interfaces
dotnet add package RoslynMcp.Contracts

Contributing

Contributions are welcome. See CONTRIBUTING.md for guidelines.

Build from Source

git clone https://github.com/JoshuaRamirez/RoslynMcpServer.git
cd RoslynMcpServer
dotnet build -c Release

Run Tests

# All tests
dotnet test

# Specific test projects
dotnet test tests/RoslynMcp.Core.Tests
dotnet test tests/RoslynMcp.Server.Tests
dotnet test tests/RoslynMcp.Cli.Tests

License

This project is licensed under the MIT License. See the LICENSE file for details.

Acknowledgments

Built with Roslyn -- the .NET Compiler Platform
Implements the Model Context Protocol

Support

Issues: GitHub Issues
Discussions: GitHub Discussions

Name		Name	Last commit message	Last commit date
Latest commit History 48 Commits
.claude-plugin		.claude-plugin
.github		.github
Design		Design
commands		commands
src		src
testdata/TestSolution		testdata/TestSolution
tests		tests
.editorconfig		.editorconfig
.gitignore		.gitignore
.mcp.json.example		.mcp.json.example
CHANGELOG.md		CHANGELOG.md
CODE_OF_CONDUCT.md		CODE_OF_CONDUCT.md
CONTRIBUTING.md		CONTRIBUTING.md
IMPLEMENTATION_SUMMARY.md		IMPLEMENTATION_SUMMARY.md
LICENSE		LICENSE
PUBLIC_REVIEW_SUMMARY.md		PUBLIC_REVIEW_SUMMARY.md
README.md		README.md
RELEASE_CHECKLIST.md		RELEASE_CHECKLIST.md
RoslynMcp.sln		RoslynMcp.sln
SECURITY.md		SECURITY.md
global.json		global.json
init-repo.ps1		init-repo.ps1

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Roslyn MCP Server

Table of Contents

Why RoslynMcpServer?

Prerequisites

Quick Start

1. Install

2. Configure

3. Verify

4. Try It

Standalone CLI

Install

Usage

Examples

Configuration

Claude Code

Claude Desktop

Available Tools

Move and Rename

Extract

Inline

Signature and Encapsulation

Generate

Convert

Using Directives

Diagnostics

Code Navigation

Analysis & Metrics

Code Generation

Preview Mode

Troubleshooting

.NET 9 SDK not found

MSBuild or solution loading issues

Using the diagnose tool

NuGet Libraries

Contributing

Build from Source

Run Tests

License

Acknowledgments

Support

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