DotLens

A Model Context Protocol (MCP) server that gives AI coding agents deep .NET/C# code analysis capabilities — impact analysis, dead code detection, complexity metrics, data flow analysis, and more — built on Microsoft Roslyn.

Complements your agent's built-in LSP support with semantic analysis tools that go beyond standard navigation.

Quick Start

1. Install:

   dotnet tool install -g DotLens.MCP
   

2. Add .mcp.json to your project root:

   {
     "mcpServers": {
       "dotlens": {
         "type": "stdio",
         "command": "dotlens",
         "args": []
       }
     }
   }
   

3. Restart your MCP client (e.g., Claude Code) to load the server.

If your project root contains exactly one .sln or .slnx file, DotLens auto-loads it on startup — no additional configuration needed.

What Does DotLens Add Over Native LSP?

AI agents like Claude Code already have built-in LSP support for C# (navigation, diagnostics, references). Both DotLens and the native LSP use Roslyn under the hood. The difference is what they expose:

LSP provides standard editor operations — go-to-definition, find references, diagnostics after edits, rename. These run automatically and are tightly integrated.

DotLens adds analysis and refactoring tools that the LSP protocol doesn't define:

Capability	What it does
Impact analysis	What breaks if I change this symbol? (analyze_change_impact)
Dead code detection	Find unused types, methods, and fields across the solution (find_unused_code)
Complexity metrics	Cyclomatic, cognitive, nesting depth, LOC per method (get_complexity_metrics)
Data flow analysis	Track variable assignments and usage through a method (analyze_data_flow)
Control flow analysis	Branching paths and reachability (analyze_control_flow)
Dependency graph	Project-level dependency visualization with cycle detection (dependency_graph)
Semantic search	Find symbols by accessibility, modifiers, return type, attributes (find_symbols)
Compound queries	Signature + callers + outgoing calls in one call (analyze_method)
Code generation	Generate interface stubs, null checks, apply bulk fixes (implement_missing_members, fix_all)

DotLens also overlaps with LSP for navigation (find references, go-to-definition, type hierarchy, etc.). These overlapping tools return AI-optimized structured JSON with verbosity control and pagination, which can be more token-efficient than LSP responses for large results.

Installation

Via NuGet (Recommended)

dotnet tool install -g DotLens.MCP

Then run with:

dotlens

Build from Source

git clone https://github.com/alphaleonis/dotlens-mcp.git
cd dotlens-mcp
dotnet build -c Release
dotnet test
dotnet publish src/DotLens/DotLens.csproj -c Release -o ./publish

Configuration

All options use the DOTLENS_ prefix for environment variables:

Environment Variable	Description	Default	Range
DOTLENS_SolutionPath	Solution file (.sln/.slnx) or directory to search	None	-
DOTLENS_AutoLoadSolution	Auto-detect solution from working directory	true	-
DOTLENS_LogLevel	Logging verbosity	Warning	Verbose, Debug, Information, Warning, Error
DOTLENS_TimeoutSeconds	Timeout for long-running operations	30	1-600
DOTLENS_LoadWaitTimeoutSeconds	Seconds to wait for in-progress load before returning "loading" status	5	1-60
DOTLENS_MaxDiagnostics	Maximum diagnostics to return	100	1-10000
DOTLENS_UseAbsolutePaths	Use absolute paths instead of relative	false	-
DOTLENS_MaxCacheSize	Maximum documents to cache	500	1-10000
DOTLENS_CacheExpirationMinutes	Cache sliding expiration	30	1-1440
DOTLENS_EnableSemanticCache	Enable document caching	true	-

Options can also be set via command-line arguments: dotlens --LogLevel=Debug

Solution Auto-Loading

DotLens automatically discovers and loads a solution in the background on startup. The MCP server starts accepting connections immediately — no waiting for large solutions to load.

Condition	Behavior
DOTLENS_SolutionPath points to a file	Loads that solution directly
DOTLENS_SolutionPath points to a directory	Searches that directory for solutions
One .sln/.slnx in working directory	Auto-loads it
Multiple solutions in working directory	Logs which were found; call load_solution to choose
No solutions found	Call load_solution manually

If a tool is called before loading completes, it returns a "No solution loaded" error. If load_solution is called while auto-load is in progress, it waits up to DOTLENS_LoadWaitTimeoutSeconds (default 5s) and returns a "loading" status if still in progress. Use health_check to monitor loading progress.

Relative SolutionPath values are resolved relative to the working directory. Set DOTLENS_AutoLoadSolution=false to disable auto-discovery.

Tools

Navigation

Tool	Description
go_to_definition	Jump to symbol definition
find_references	All references across solution
find_implementations	Interface/abstract implementations
find_callers	Impact analysis — who calls this?
find_overrides	Find all overrides of a virtual/abstract member
find_base_member	Find the base/interface member that a method overrides or implements
get_type_hierarchy	Inheritance chain
get_symbol_info	Semantic info at position

Search

Tool	Description
search_symbols	Glob pattern search (*Handler, Get*)
find_symbols	Find symbols by name and/or semantic filters (kind, accessibility, async, etc.)
get_type_members	All members by type name
get_derived_types	Find all subclasses
get_method_info	Method signatures for all overloads
get_file_outline	File skeleton with type declarations and member signatures
get_containing_member	Get enclosing method/property/type at a position
get_attributes	Find all symbols decorated with a specific attribute
find_string_literals	Find string literals across the solution

Compound Analysis

Tool	Description
get_type_overview	Full type info in one call
analyze_method	Signature + callers + outgoing calls + location
get_file_overview	File summary with diagnostics
get_method_source	Source code by name (use instead of reading entire files)
get_instantiation_options	How to create a type
check_type_compatibility	Can A assign to B?
get_outgoing_calls	What does this method call?
analyze_change_impact	What breaks if changed?
get_missing_members	Interface/abstract members that must be implemented
get_type_members_batch	Multiple types in one call

Analysis

Tool	Description
get_diagnostics	Compiler errors/warnings
analyze_data_flow	Variable assignments and usage
analyze_control_flow	Branching/reachability
get_complexity_metrics	Cyclomatic, nesting, LOC, cognitive
find_unused_code	Dead code detection
get_project_structure	Solution structure
dependency_graph	Project dependencies
get_project_packages	NuGet packages referenced by projects
fix_all	Apply a code fix to all occurrences of a diagnostic

Refactoring

Tool	Description
rename_symbol	Safe rename across solution
get_code_actions	Available Roslyn refactorings/fixes at a position
apply_code_action	Apply a Roslyn code action by title or key
add_null_checks	Generate ArgumentNullException guards
add_using	Add a using directive (skips if present, auto-sorts)
implement_missing_members	Generate interface/abstract stubs

Formatting

Tool	Description
organize_usings	Sort/remove unused (document/project/solution scope)
format_document_batch	Format documents using Roslyn's Formatter (respects .editorconfig)

Editing

Tool	Description
edit_file	Batch find/replace with atomic apply + diagnostics
write_file	Full file replacement with atomic apply + diagnostics

Infrastructure

Tool	Description
health_check	Server status
load_solution	Load .sln/.slnx for analysis
unload_solution	Unload solution and release file locks
reload_solution	Reload solution to pick up new files/project changes
list_solutions	List all loaded solutions and which is active
set_active_solution	Switch active solution context
sync_documents	Sync in-memory workspace after external file edits

AI Agent Configuration Tips

AI agents tend to default to their built-in tools (Grep, Read, LSP) even when DotLens provides a better option. To get the most out of DotLens, nudge your agent toward using it for analysis tasks.

Claude Code — add to your project's CLAUDE.md:

For C# code, prefer DotLens tools for analysis beyond basic navigation:
- Use `analyze_change_impact` before refactoring to understand blast radius
- Use `find_unused_code` instead of manual searching for dead code
- Use `get_complexity_metrics` to identify problem methods
- Use `get_method_source` instead of Read for viewing specific methods (saves tokens)
- Use `search_symbols` / `find_symbols` instead of Grep for finding C# symbols

Other MCP clients — configure similar tool priority in your agent's system prompt.

Document Synchronization

DotLens maintains an in-memory representation of your solution for fast queries. When files are modified externally (via Edit/Write tools), the agent is responsible for synchronizing changes.

When to call sync_documents

Action	Call sync_documents?
Used Edit tool to modify .cs files	Yes
Used Write tool to create new .cs files	Yes
Deleted .cs files	Yes
Used DotLens refactoring tools (rename, extract, etc.)	No (auto-updated)
Used DotLens editing tools (edit_file, write_file)	No (auto-updated + returns diagnostics)
Modified .csproj files	No (use reload_solution instead)

# After editing specific files
sync_documents(filePaths: ["src/MyClass.cs", "src/MyService.cs"])

# After bulk changes — sync all documents
sync_documents()

This mirrors how LSP works — the client (editor) notifies the server of changes. This approach eliminates race conditions, avoids file watcher complexity, and gives agents explicit control over workspace state.

If you don't sync, queries may return stale data (old method signatures, missing new files, etc.).

Architecture

DotLens uses the official MCP C# SDK with a two-process architecture for file lock isolation:

MCP Client (AI Agent)
        │ stdin/stdout (MCP protocol)
        ▼
Server Process
  ├─ MCP Server: handles client requests
  ├─ MCP Client: forwards tool calls to worker
  └─ Server-side tools: load/unload/reload/list/set_active/health
        │
        ▼
Worker Process (--worker mode)
  ├─ MCP Server: receives forwarded calls
  ├─ MSBuildWorkspace: holds file locks
  └─ Roslyn semantic analysis tools
        │
        ▼
Microsoft.CodeAnalysis (Roslyn)
  └─ MSBuildWorkspace, SemanticModel, SymbolFinder

This architecture allows the worker process to be killed and restarted to release file locks — important when rebuilding projects with source generators.

Requirements

• .NET 10.0 SDK or Runtime
• An MCP-compatible AI agent (e.g., Claude Code, Cursor, VS Code + Copilot)

Contributing

Contributions are welcome! Please open an issue or pull request on GitHub.

# Development workflow
dotnet build src/DotLens/DotLens.csproj
dotnet test tests/DotLens.Tests/DotLens.Tests.csproj

Adding New Tools

Create or update a tool class in src/DotLens/Tools/:

[McpServerToolType]
public class YourTools
{
    private readonly IWorkspaceManager _workspace;

    public YourTools(IWorkspaceManager workspace) => _workspace = workspace;

    [McpServerTool(Name = "your_tool", ReadOnly = true, OpenWorld = false)]
    [Description("Description shown to AI.")]
    public async Task<string> YourTool(
        [Description("Param description")] string filePath,
        [Description("Optional param")] int? maxResults = 50,
        CancellationToken cancellationToken = default)
    {
        _workspace.EnsureSolutionLoaded();
        // Your logic using _workspace.Solution, etc.
        return ToolResponse.Success(new { /* results */ });
    }
}

No separate tool definition needed — the MCP SDK generates schemas from attributes.

Key Directories

Directory	Purpose
src/DotLens/Tools/Navigation/	Symbol navigation (go-to-definition, find references, etc.)
src/DotLens/Tools/Search/	Symbol search, type members, file outline
src/DotLens/Tools/Intelligence/	Compound analysis (type overview, method analysis, etc.)
src/DotLens/Tools/Analysis/	Diagnostics, data/control flow, complexity, project structure
src/DotLens/Tools/Refactoring/	Rename, code actions, null checks, implement members
src/DotLens/Tools/Formatting/	Organize usings, format documents
src/DotLens/Tools/Editing/	File editing with diagnostics
src/DotLens/Tools/Server/	Solution management (load/unload/reload)
src/DotLens/Infrastructure/	Shared utilities (WorkspaceManager, MultiWorkerManager, etc.)
tests/DotLens.Tests/	xUnit integration tests

Acknowledgments

DotLens builds on the work of dotnet-roslyn-mcp by Brendan Kowitz and SharpLensMcp by Peter Zalutski.

License

MIT — See LICENSE for details.