Roslyn CodeLens MCP Server

A Roslyn-based MCP server that provides 22 semantic code intelligence tools for .NET codebases. Designed for use with Claude Code to understand type hierarchies, call sites, DI registrations, and reflection usage.

Features

• find_implementations — Find all classes/structs implementing an interface or extending a class
• find_callers — Find every call site for a method, property, or constructor
• get_type_hierarchy — Walk base classes, interfaces, and derived types
• get_di_registrations — Scan for DI service registrations
• get_project_dependencies — Get the project reference graph
• get_symbol_context — One-shot context dump for any type
• find_reflection_usage — Detect dynamic/reflection-based usage
• find_references — Find all references to any symbol (types, methods, properties, fields, events)
• go_to_definition — Find the source file and line where a symbol is defined
• get_diagnostics — List compiler errors, warnings, and Roslyn analyzer diagnostics
• get_code_fixes — Get available code fixes with structured text edits for any diagnostic
• search_symbols — Fuzzy workspace symbol search by name
• get_nuget_dependencies — List NuGet package references per project
• find_attribute_usages — Find types and members decorated with a specific attribute
• find_circular_dependencies — Detect cycles in project or namespace dependency graphs
• get_complexity_metrics — Cyclomatic complexity analysis per method
• find_naming_violations — Check .NET naming convention compliance
• find_large_classes — Find oversized types by member or line count
• find_unused_symbols — Dead code detection via reference analysis
• get_source_generators — List source generators and their output per project
• get_generated_code — Inspect generated source code from source generators
• rebuild_solution — Force a full reload of the analyzed solution

Installation

As a Claude Code Plugin

claude install gh:MarcelRoozekrans/roslyn-codelens-mcp

As a .NET Global Tool

dotnet tool install -g RoslynCodeLens.Mcp

Manual MCP Configuration

Add to your Claude Code MCP settings:

{
  "mcpServers": {
    "roslyn-codelens": {
      "command": "roslyn-codelens-mcp",
      "args": [],
      "transport": "stdio"
    }
  }
}

Usage

The server automatically discovers .sln files by walking up from the current directory. You can also pass a solution path directly:

roslyn-codelens-mcp /path/to/MySolution.sln

Performance

All type lookups use pre-built reverse inheritance maps, member indexes, and attribute indexes for O(1) access. Benchmarked on an i9-12900HK with .NET 10.0.3:

Tool	Latency	Memory
find_circular_dependencies	288 ns	1.3 KB
get_project_dependencies	299 ns	1.2 KB
go_to_definition	442 ns	568 B
get_type_hierarchy	720 ns	856 B
find_implementations	804 ns	704 B
get_symbol_context	1.1 µs	1.0 KB
get_source_generators	2.6 µs	8.3 KB
find_attribute_usages	6.8 µs	312 B
get_generated_code	13 µs	9.8 KB
get_diagnostics	27 µs	23 KB
get_complexity_metrics	50 µs	5.8 KB
find_large_classes	60 µs	1.2 KB
get_di_registrations	60 µs	13 KB
get_nuget_dependencies	62 µs	16 KB
find_reflection_usage	82 µs	15 KB
find_callers	182 µs	38 KB
search_symbols	517 µs	2.4 KB
find_references	927 µs	208 KB
find_unused_symbols	1.1 ms	212 KB
find_naming_violations	5.0 ms	670 KB
Solution loading (one-time)	~928 ms	8 MB

Hot Reload

The server watches .cs, .csproj, .props, and .targets files for changes. When a change is detected, affected projects are lazily re-compiled on the next tool query — only stale projects and their downstream dependents are re-compiled, not the full solution.

Location-returning tools include an IsGenerated flag to distinguish source-generator output from hand-written code.

Requirements

• .NET 10 SDK
• A .NET solution with compilable projects

Development

dotnet build
dotnet test
dotnet run --project benchmarks/RoslynCodeLens.Benchmarks -c Release

License

MIT