Best for
- .NET/C# developers using MCP clients like Claude Code or VS Code
- AI-assisted development workflows needing deep static analysis and safe refactoring
- Teams maintaining large SDK-style .NET solutions
R
Roslyn CodeLens MCP Server
Community
Roslyn-based semantic .NET/C# intelligence for AI agents
GitHub source repository ↗
68FMRS · C
A very comprehensive Roslyn semantic-analysis MCP server with 67 tools covering navigation, refactoring, test intelligence, quality auditing, and IL inspection. Performance is benchmarked, and a VS-style trust model guards analyzer execution. Works only with SDK-style .NET projects and requires the .NET 10 SDK. Maintained by an individual developer, not an official .NET/Roslyn product.
Roslyn CodeLens is a Roslyn-based MCP server that gives AI agents deep semantic understanding of .NET/C# codebases over stdio. It exposes 67 tools for navigation, call graphs, diagnostics and code fixes, safe refactoring, code-quality auditing, test intelligence, DI graphs, and IL/external-assembly inspection. Installable via npm (npx launcher), NuGet (.NET global tool), Claude Code plugin, or Docker; requires the .NET 10 SDK.
Tools
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
find_event_subscribers
Find every += / -= site for an event symbol with resolved handler
find_tests_for_symbol
List xUnit/NUnit/MSTest methods exercising a production symbol, with optional transitive walk
get_test_summary
Per-project inventory of test methods with framework, attributes, data rows, and locations
find_uncovered_symbols
Find public methods/properties no test reaches, sorted by cyclomatic complexity
generate_test_skeleton
Emit a compilable test-class skeleton (as text) with auto-detected test framework
get_type_hierarchy
Walk base classes, interfaces, and derived types
get_di_registrations
Scan for DI service registrations (generic, typeof-pair, and factory-lambda forms)
get_instantiation_options
Answer 'how do I construct this type' with constructors, factories, DI registrations, and required members
get_project_dependencies
Get the project reference graph
get_symbol_context
One-shot context dump for any type
get_public_api_surface
Enumerate every public/protected type and member in production projects
find_breaking_changes
Diff the current API against a baseline JSON or DLL and report breaking changes
find_reflection_usage
Detect dynamic/reflection-based usage
get_exception_flow
Report exceptions that escape a method with their propagation paths
find_throw_sites
Find every site an exception type is thrown, optionally including derived types
find_catch_blocks
Find every catch for a type, flagging filtered, rethrowing, and swallowing handlers
find_references
Find all references to a symbol, tagged with kinds like read/write/invocation
go_to_definition
Find the source file and line where a symbol is defined
get_method_source
Fetch full declaration source for one or many members by name in a single call
resolve_stack_trace
Map a pasted .NET stack trace to file/line/symbol, undoing compiler name mangling
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_obsolete_usage
List every [Obsolete] call site grouped by deprecation message and severity
find_circular_dependencies
Detect cycles in project or namespace dependency graphs
check_architecture
Enforce layering rules against the real semantic type graph
get_complexity_metrics
Report cyclomatic complexity, cognitive complexity, and max nesting depth per member
find_naming_violations
Check .NET naming convention compliance
find_async_violations
Detect sync-over-async, async void misuse, missing awaits, and fire-and-forget tasks
find_disposable_misuse
Detect IDisposable/IAsyncDisposable instances not wrapped in using/await using
find_large_classes
Find oversized types by member or line count
find_god_objects
Find types combining high size with high cross-namespace coupling
find_unused_symbols
Dead code detection via reference analysis with automatic filtering of tests and generated code
get_project_health
Composite audit aggregating 7 quality dimensions per project
get_source_generators
List source generators and their output per project
get_generated_code
Inspect generated source code from source generators
inspect_external_assembly
Browse types, members, and XML docs from closed-source assemblies
peek_il
Decompile any method to ilasm-style IL bytecode
get_code_actions
Discover available refactorings and fixes at any position
apply_code_action
Execute any Roslyn refactoring by title, with preview mode
rename_symbol
Solution-wide safe rename via Roslyn's Renamer with preview and conflict reporting
change_signature
Add, remove, and reorder method parameters and rewrite every call site
list_solutions
List all loaded solutions and which one is currently active
set_active_solution
Switch the active solution by partial name
load_solution
Load an additional .sln/.slnx at runtime and make it active
unload_solution
Unload a loaded solution to free memory
rebuild_solution
Force a full reload of the analyzed solution
start_background_task
Queue a long-running tool to run in the background
get_task_status
Get status, result, or error of a background task by taskId
list_running_tasks
List background tasks running or completed within the last 5 minutes
trust_solution
Authorize a solution to run Roslyn analyzers
list_trusted_paths
Inspect the persistent trust store and session-trusted solutions
revoke_trust
Revoke previously-granted trust for a solution path
analyze_data_flow
Variable read/write/capture analysis within a statement range
analyze_control_flow
Branch/loop reachability analysis within a statement range
analyze_change_impact
Show all files, projects, and call sites affected by changing a symbol
get_type_overview
Compound tool: type context + hierarchy + file diagnostics in one call
analyze_method
Compound tool: method signature + callers + outgoing calls in one call
get_overloads
Every overload of a method/constructor with full parameter detail
get_extension_methods
Every extension member applicable to a type, including C# 14 extension blocks
get_operators
Every user-defined and conversion operator on a type
get_call_graph
Transitive caller/callee graph with depth bound and cycle detection
get_file_overview
Compound tool: types in a file + file-scoped diagnostics in one call
Setup
npm: add "mcpServers": {"roslyn-codelens": {"type": "stdio", "command": "npx", "args": ["-y", "roslyn-codelens-mcp"]}} to your MCP client config; the .NET 10 SDK must be on PATH. NuGet: run dotnet tool install -g RoslynCodeLens.Mcp then configure command roslyn-codelens-mcp, or use dnx RoslynCodeLens.Mcp --yes. Claude Code: claude install gh:MarcelRoozekrans/roslyn-codelens-mcp. Docker is also supported, bind-mounting the solution at /workspace (solution must be restored).
claude_desktop_config.json
{"mcpServers":{"roslyn-codelens":{"type":"stdio","command":"npx","args":["-y","roslyn-codelens-mcp"]}}}
Fit and risk
Not for
- Non-.NET/C# codebases
- Legacy non-SDK-style csproj projects (skipped with a warning)
- Environments without the .NET 10 SDK (unless using Docker)
Required permissions
- Reads and analyzes .NET solutions and source files on disk
- Tools like apply_code_action can write/modify source files (preview mode available)
- Running Roslyn analyzer DLLs requires explicit trust via trust_solution
Risks and side effects
- Analyzer DLLs execute in-process; the trust model restricts them to NuGet global packages, the dotnet SDK dir, or solution bin/obj, but grant trust carefully
- apply_code_action, rename_symbol, and change_signature modify source files directly; prefer preview mode first
- The stdio server has read/write access to the loaded codebase
- Solutions must be NuGet-restored before loading or reference resolution may fail
Troubleshooting
- Verify the .NET 10 SDK is installed and on PATH (required by the npx launcher)
- Solutions must be compilable SDK-style projects; legacy projects are skipped and listed in SkippedProjects
- If diagnostics with analyzers return SolutionNotTrusted, authorize the solution via trust_solution
- Project load timeouts (default 300s) are recorded as SkippedProjects; adjust ROSLYN_CODELENS_OPEN_PROJECT_TIMEOUT_SECONDS
- Docker output reports container paths, and the mounted solution must be restored
- If a symbol is not found, confirm the solution is loaded and active via list_solutions
Use cases
Give AI agents semantic navigation and call-graph analysis of .NET codebases
Perform safe solution-wide renames and signature changes
Audit code quality: complexity, naming, async misuse, dead code
Find untested public symbols via test intelligence and generate test skeletons
Inspect types and IL of closed-source NuGet dependencies
Supported clients
Claude CodeFull support
VS CodeFull support
Visual StudioFull support