RoslynLens 1.1.1
dotnet tool install --global RoslynLens --version 1.1.1
This package contains a .NET tool you can call from the shell/command line.
dotnet new tool-manifest
dotnet tool install --local RoslynLens --version 1.1.1
This package contains a .NET tool you can call from the shell/command line.
#tool dotnet:?package=RoslynLens&version=1.1.1
The NuGet Team does not provide support for this client. Please contact its maintainers for support.
nuke :add-package RoslynLens --version 1.1.1
The NuGet Team does not provide support for this client. Please contact its maintainers for support.
RoslynLens
A token-efficient MCP (Model Context Protocol) server for .NET codebase navigation, powered by Roslyn semantic analysis. Designed for use with Claude Code.
Instead of reading entire .cs files (500-2000+ tokens each), Claude Code
queries this MCP server and receives focused, semantic results (30-150
tokens). This dramatically reduces token consumption when working with
large .NET solutions.
Features
28 Navigation & Analysis Tools
| Tool | Purpose |
|---|---|
find_symbol |
Locate type/method definitions by name (supports glob patterns) |
find_references |
Find all usages of a symbol |
find_implementations |
Find interface implementors and derived classes |
find_callers |
Find direct callers of a method |
find_overrides |
Find overrides of virtual/abstract methods |
find_dead_code |
Detect unused types, methods, and properties (with filters) |
get_type_hierarchy |
Show inheritance chain, interfaces, and derived types |
get_public_api |
Get public surface without reading the full file |
get_symbol_detail |
Full signature, parameters, return type, and XML docs |
get_project_graph |
Solution dependency tree (with filtering for large solutions) |
get_dependency_graph |
Method call chain visualization |
get_diagnostics |
Compiler warnings and errors |
get_test_coverage_map |
Heuristic test coverage mapping |
get_complexity_metrics |
Cyclomatic, cognitive complexity, nesting depth, LOC |
detect_antipatterns |
18 anti-pattern detectors |
detect_circular_dependencies |
Project and type-level cycle detection |
detect_duplicates |
Structurally similar code detection via AST fingerprinting |
get_module_depends_on |
[DependsOn] attribute graph (modular monoliths) |
validate_conventions |
Convention violation checker |
analyze_method |
Compound: signature + callers + dependencies + complexity |
get_type_overview |
Compound: public API + hierarchy + implementations + diagnostics |
get_file_overview |
Compound: types + diagnostics + anti-patterns for a file |
analyze_data_flow |
Variable assignments, reads, writes, captured variables |
analyze_control_flow |
Reachability, return points, exit points |
find_symbols_batch |
Resolve multiple symbol names in one call |
get_public_api_batch |
Get public API of multiple types in one call |
get_symbol_detail_batch |
Get details of multiple symbols in one call |
resolve_external_source |
Resolve NuGet/framework source via SourceLink or decompilation |
18 Anti-Pattern Detectors
General .NET detectors:
| ID | Detector | Description |
|---|---|---|
| AP001 | AsyncVoidDetector | async void methods (except event handlers) |
| AP002 | SyncOverAsyncDetector | .Result, .Wait(), .GetAwaiter().GetResult() |
| AP003 | HttpClientInstantiationDetector | new HttpClient() instead of IHttpClientFactory |
| AP004 | DateTimeDirectUseDetector | DateTime.Now/UtcNow instead of TimeProvider |
| AP005 | BroadCatchDetector | catch (Exception) without re-throw |
| AP006 | LoggingInterpolationDetector | String interpolation in log calls |
| AP007 | PragmaWithoutRestoreDetector | #pragma warning disable without matching restore |
| AP008 | MissingCancellationTokenDetector | Async methods missing CancellationToken parameter |
| AP009 | EfCoreNoTrackingDetector | EF Core queries without .AsNoTracking() |
Domain-specific detectors:
| ID | Detector | Description |
|---|---|---|
| GR-GUID | GuidNewGuidDetector | Guid.NewGuid() instead of IGuidGenerator |
| GR-SECRET | HardcodedSecretDetector | Hardcoded passwords, connection strings, API keys |
| GR-SYNC-EF | SynchronousSaveChangesDetector | SaveChanges() instead of SaveChangesAsync() |
| GR-BADREQ | TypedResultsBadRequestDetector | TypedResults.BadRequest<string>() instead of Problem() |
| GR-REGEX | NewRegexDetector | new Regex() instead of [GeneratedRegex] |
| GR-SLEEP | ThreadSleepDetector | Thread.Sleep() in production code |
| GR-CONSOLE | ConsoleWriteDetector | Console.Write/WriteLine instead of ILogger |
| GR-CFGAWAIT | MissingConfigureAwaitDetector | Missing ConfigureAwait(false) in library code |
| GR-DTO | DtoSuffixDetector | Classes/records with *Dto suffix |
Requirements
- .NET 10 SDK or later
- A .NET solution (
.slnor.slnx)
Installation
dotnet tool install --global RoslynLens
Usage
With Claude Code (recommended)
Add to your Claude Code MCP configuration:
# User-scoped (available in all projects)
claude mcp add --scope user --transport stdio roslyn-lens -- roslyn-lens
# Project-scoped
claude mcp add --transport stdio roslyn-lens -- roslyn-lens
Or via .mcp.json in your project root:
{
"mcpServers": {
"roslyn-lens": {
"type": "stdio",
"command": "roslyn-lens",
"args": []
}
}
}
Solution Discovery
The server automatically finds the nearest .sln or .slnx file using
BFS from the current directory (max 3 levels up). You can also specify a
solution explicitly:
roslyn-lens --solution /path/to/MySolution.slnx
Standalone
roslyn-lens
The server communicates over stdio using the MCP protocol.
Building from Source
git clone https://github.com/jfmeyers/roslyn-lens.git
cd roslyn-lens
dotnet build
dotnet test
Pack and install locally
dotnet pack -c Release -o ./nupkgs
dotnet tool install --global --add-source ./nupkgs RoslynLens
Configuration
Environment variables for runtime tuning:
| Variable | Purpose | Default |
|---|---|---|
ROSLYN_LENS_TIMEOUT_SECONDS |
Operation timeout | 30 |
ROSLYN_LENS_MAX_RESULTS |
Maximum results per query | 100 |
ROSLYN_LENS_CACHE_SIZE |
LRU compilation cache size | 50 |
ROSLYN_LENS_LOG_LEVEL |
Log verbosity (Trace/Debug/Information/Warning/Error) | Information |
Architecture
src/RoslynLens/
├── Program.cs # Host + MCP stdio transport
├── SolutionDiscovery.cs # BFS .sln/.slnx auto-discovery
├── WorkspaceManager.cs # MSBuildWorkspace, LRU compilation cache
├── WorkspaceInitializer.cs # Background solution loading
├── SymbolResolver.cs # Cross-project symbol resolution + fuzzy FQN
├── RoslynLensConfig.cs # Environment variable configuration
├── WorkspaceState.cs # Workspace loading state enum
├── ComplexityAnalyzer.cs # Cyclomatic/cognitive complexity metrics
├── DuplicateCodeDetector.cs # AST fingerprinting for duplicate detection
├── ExternalSourceResolver.cs # SourceLink + decompilation for NuGet deps
├── Tools/ # 28 MCP tool implementations
├── Analyzers/ # 18 anti-pattern detectors
└── Responses/ # Token-optimized DTOs
Key design decisions:
- Lazy compilation: Solutions with 50+ projects only compile on-demand (LRU cache of 50 compilations)
- File watcher:
.cschanges trigger incremental text updates;.csprojchanges trigger full reload - Background loading: Solution loads asynchronously; tools return "loading" status until ready
- Logs to stderr: All logging goes to stderr to keep stdout clean for JSON-RPC
Acknowledgments
Inspired by CWM.RoslynNavigator by Mukesh Murugan (MIT License). Adapted with additional detectors, auto-discovery, and global tool distribution.
Documentation
Full documentation is available in the docs/ directory.
Author
JF Meyers — GitHub
License
| Product | Versions Compatible and additional computed target framework versions. |
|---|---|
| .NET | net10.0 is compatible. net10.0-android was computed. net10.0-browser was computed. net10.0-ios was computed. net10.0-maccatalyst was computed. net10.0-macos was computed. net10.0-tvos was computed. net10.0-windows was computed. |
Compatible target framework(s)
Included target framework(s) (in package)
Learn more about Target Frameworks and .NET Standard.
This package has no dependencies.