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Roslyn MCP Server

Build and Test Code Quality NuGet NuGet Downloads License: MIT

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 62 Roslyn-powered tools to AI assistants and other MCP clients. It combines 36 refactoring operations, 5 code navigation tools, 6 analysis and metrics tools, 5 code generation tools, and 10 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.

Table of Contents

Why RoslynMcpServer?

  • 62 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:

  1. .NET 9.0 SDK or later -- Download here
  2. 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 62 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
rename_file_to_match_type Rename a source file so its name matches the primary type declared in it, without renaming the type or its references. sourceFile, typeName, line, column
rename_namespace Rename a C# namespace across the solution, updating declarations, using directives, and qualified name references. Does not move folders by default. sourceFile, namespaceName, newName, line, column, updateFolders

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, replaceAll
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, separateFile
extract_base_class Extract members (methods, properties, fields, and events) to a new base class. Field-like and accessor-style events move by name; a multi-variable event field moves only the selected declarator. Private events become protected on the new base. makeAbstract still only marks the new class abstract. sourceFile, typeName, baseClassName, members, targetFile, separateFile, makeAbstract
pull_members_up Move selected members (methods, properties, fields, and events) from a derived type onto an existing base class or interface. Field-like and accessor-style events move by name; a multi-variable event field moves only the selected declarator. Private events become protected on the base. makeAbstract on a class target makes the event abstract and keeps an override on the derived type; interface targets keep the implementation on the derived type. sourceFile, typeName, members, targetBaseType, makeAbstract
push_members_down Move selected members (methods, properties, fields, and events) from a base type down onto derived types. Field-like and accessor-style events move by name; a multi-variable event field moves only the selected declarator. leaveAbstract on a class source makes the event abstract on the base and adds an override on each derived type. sourceFile, typeName, members, targetDerivedTypes, leaveAbstract
use_base_type Replace derived-type references with a compatible base type or interface. sourceFile, typeName, targetBaseType
introduce_field Turn a selected local variable or expression into a class field, optionally initializing it in a constructor. sourceFile, startLine, startColumn, endLine, endColumn, fieldName, isReadonly, isStatic, initializeInConstructor, replaceAll
safe_delete Delete a selected symbol only when it has no remaining references. If usages exist, reject with their locations. sourceFile, startLine, startColumn, endLine, endColumn, symbolName
make_static Make a selected instance method static when it does not use instance state. Adds the static modifier and updates call sites and method-group conversions to the containing type name. sourceFile, startLine, startColumn, endLine, endColumn, symbolName
make_non_static Make a selected static method an instance method when a valid instance receiver exists. Removes the static modifier and updates type-name call sites and method-group conversions to an instance receiver (or this in the same type). sourceFile, startLine, startColumn, endLine, endColumn, symbolName

Inline

Tool Description Key Parameters
inline_method Inline a method by replacing call sites with the method body. Optionally remove the method. sourceFile, methodName, line, column, callSiteLocation, removeMethod
inline_variable Inline a local variable by replacing all usages with its initializer value. sourceFile, variableName, line
inline_constant Inline a const field by replacing references with a formatted literal. Optionally remove the constant. sourceFile, constantName, typeName, removeConstant

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
add_parameter Add a named parameter to a method and update call sites, overrides, and interface implementations. sourceFile, methodName, parameterName, parameterType, defaultValue, position, line, column, updateOverrides, updateImplementations
remove_parameter Remove a named parameter from a method and drop matching call-site arguments, updating overrides and interface implementations. sourceFile, methodName, parameterName, line, column, force, updateOverrides, updateImplementations
reorder_parameters Reorder a method's parameters by a 0-based permutation and update positional call-site arguments, updating overrides and interface implementations. sourceFile, methodName, newOrder, line, column, updateOverrides, updateImplementations
change_return_type Change a method's return type and update return statements when the conversion is safe, updating overrides and interface implementations. sourceFile, methodName, newReturnType, line, column, updateOverrides, updateImplementations, convertReturnStatements
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 (includeProperties: default true includes settable properties, false uses instance fields only unless members names a property; includeInheritedMembers: default false keeps this-type-only collection, true also collects accessible instance fields and, when includeProperties is true, settable properties declared on base types; replaceExisting: replace an existing constructor with the exact same signature instead of failing — optional-parameter / required-parameter ambiguity still fails; visibility: default public, also private / protected / internal / protected internal / private protected; structs/record structs reject the three protected forms; unsealed-record copy constructors must be public or protected (CS8878); copyConstructor: default false keeps today's one-parameter-per-member constructor, true generates a single same-type copy constructor that assigns each selected member from that parameter — derived records whose base is also a record include : base(other); classBaseCopy: default false keeps today's class copy-constructor shape, true (requires copyConstructor) emits : base((Base)other) on an ordinary class when the immediate base has an accessible Base(Base) copy constructor and does not reassign inherited members; callBase: default false keeps today's non-copy shape (no : base(...)), true emits : base(...) on an ordinary class or record class when an accessible immediate-base constructor's parameter types are a prefix of the generated constructor — conflicts with copyConstructor; record structs / structs ignore callBase). sourceFile, typeName, members, includeProperties, includeInheritedMembers, addNullChecks, replaceExisting, visibility, copyConstructor, classBaseCopy, callBase
generate_property Generate a property on a type: auto-property { get; set; }, init-only { get; init; }, or a backing-field form when a field is the target (replaceExisting: default false keeps today's fail-on-clash; true removes the existing property of that name — including across partials — and inserts a freshly generated one; fields and methods of the same name are never removed; two same-named properties with no single target fail with NameCollision). sourceFile, typeName, propertyName, propertyType, fieldName, visibility, initOnly, replaceExisting
generate_method_stub Generate a method from an undefined call site, inferring the signature from usage (throwNotImplemented: default true emits throw new NotImplementedException();; false uses default-return / empty void bodies via SyntaxGenerationHelper.CreateDefaultReturnBody; async Task / Task<T> unwrap so the body compiles; ref / ref readonly returns still throw; replaceExisting: default false keeps today's fail-on-clash; true removes a compatible ordinary method — same name, type-parameter arity, parameter count, parameter types in order, and RefKind — including across partials, then inserts a freshly generated stub; constructors, operators, local functions, explicit interface implementations, and accessors are never replaced; two compatible ordinary methods with no single target fail with NameCollision). sourceFile, line, column, methodName, returnType, visibility, generateAsync, throwNotImplemented, replaceExisting
generate_overrides Generate override methods, properties/indexers, and events for base class virtual/abstract members (callBase: default true emits base.M(...) for non-abstract virtual methods and return base.Prop; / base.Prop = value; for non-abstract virtual properties and indexers (return base[i]; / base[i] = value;); abstract members still throw; events always use empty add/remove regardless of callBase; a cross-assembly protected internal event is emitted as protected (CS0507); internal / private protected events from another assembly are not generated; false uses default-return / empty bodies; replaceExisting: default false skips members this type already overrides; true also replaces those existing overrides — match methods by name + parameter types + RefKind, properties and events by name; two same-name existing overrides with no exact signature match fail with OverrideExists; new hiders / explicit interface implementations / non-override ordinary members are never replaced). sourceFile, typeName, members, callBase, replaceExisting
implement_interface Generate interface member implementations for a type (indexers emit this[...] indexer declarations via CreateIndexerStub; ordinary properties stay on CreatePropertyStub; throwNotImplemented: default true emits throw new NotImplementedException();; false uses default-return / empty setter bodies; ref / ref readonly getters still throw; replaceExisting: default false keeps today's only-unimplemented members and MemberAlreadyImplemented when nothing is missing; true also replaces already-implemented interface members — methods by name + parameter types + RefKind, properties and events by name, indexers by Item / this[] / display forms; two same-name existing implementations with no exact signature match fail with NameCollision before any write; explicitImplementation still selects explicit vs ordinary public stubs; preview describes generate vs replace and writes nothing). sourceFile, typeName, interfaceName, explicitImplementation, members, throwNotImplemented, replaceExisting, preview
implement_abstract Generate implementation stubs for unimplemented abstract members inherited by a selected class — methods, properties, indexers, and events (throwNotImplemented: default true emits throw new NotImplementedException();; false uses default-return / empty setter bodies; ref / ref readonly methods and getters still throw; events always use empty add/remove; a cross-assembly protected internal event is emitted as protected (CS0507); internal / private protected events from another assembly are not selected; replaceExisting: default false keeps today's only-unimplemented members and NoUnimplementedAbstractMembers when nothing is missing; true also replaces already-implemented abstract members — methods by name + parameter types + RefKind, properties and events by name, indexers by Item / this[] / display forms; two same-name existing implementations with no exact signature match fail with NameCollision before any write; new hiders / explicit interface implementations / non-override ordinary members are never replaced; preview describes generate vs replace and writes nothing). sourceFile, typeName, members, throwNotImplemented, replaceExisting, preview

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_to_block_body Convert a selected expression-bodied member (=> expr) to a block body. Methods become { return expr; } or { expr; } as appropriate; properties and accessors that are expression-bodied are converted too. sourceFile, 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_anonymous_to_class Convert an anonymous type (new { ... }) to a named class or record, replacing same-shape anonymous creations in the solution. sourceFile, line, newTypeName, column, asRecord
convert_tuple_to_struct Convert a tuple ((int X, int Y) / (1, 2) / ValueTuple) to a named struct, replacing same-shape tuple creations in the solution. sourceFile, line, newTypeName, column
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, systemFirst

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 (implementIEquatable: also add IEquatable<T> and typed Equals; generateOperators: also add == / !=; replaceExisting: replace existing equality members instead of failing; useHashCodeCombine: default true uses HashCode.Combine / builder, false uses unchecked prime-multiply; includeProperties: default true includes readable properties, false uses instance fields only unless fields names a property; callSuper: default false keeps member-only Equals/GetHashCode, true folds the immediate base type's equality into both methods; includeInheritedMembers: default false keeps this-type-only collection, true also collects accessible instance fields/properties declared on base types). sourceFile, typeName, fields, includeProperties, implementIEquatable, generateOperators, replaceExisting, useHashCodeCombine, callSuper, includeInheritedMembers
generate_tostring Generate a ToString() override for a type (format: interpolated or stringbuilder; includeProperties: default true includes readable properties, false uses instance fields only unless fields names a property; includeInheritedMembers: default false keeps this-type-only collection, true also collects accessible instance fields/properties declared on base types; replaceExisting: replace an existing parameterless ToString instead of failing; callSuper: default false keeps member-only ToString, true folds the immediate base type's ToString into the generated override). sourceFile, typeName, fields, includeProperties, format, includeInheritedMembers, replaceExisting, callSuper
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:

  1. Verify the SDK is installed: dotnet --list-sdks
  2. Make sure .NET 9.0 or later appears in the list
  3. 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:

  1. Make sure you can build the solution from the command line first: dotnet build /path/to/MySolution.sln
  2. On Windows, ensure Visual Studio Build Tools or a Visual Studio installation is available
  3. 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

Support

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Model Context Protocol server for Roslyn-powered C# refactoring operations

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