Roslyn CodeLens MCP Server

A Roslyn-based MCP server that gives AI agents deep semantic understanding of .NET codebases — type hierarchies, call graphs, DI registrations, diagnostics, and more.

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

Quick Start

VS Code / Visual Studio (via dnx)

Add to your MCP settings (.vscode/mcp.json or VS settings):

{
  "servers": {
    "roslyn-codelens": {
      "type": "stdio",
      "command": "dnx",
      "args": ["RoslynCodeLens.Mcp", "--yes"]
    }
  }
}

Claude Code Plugin

claude install gh:MarcelRoozekrans/roslyn-codelens-mcp

.NET Global Tool

dotnet tool install -g RoslynCodeLens.Mcp

Then add to your MCP client config:

{
  "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

roslyn-codelens-mcp