Configuration Reference

RoslynLens is configured via environment variables and CLI arguments.

Environment variables

All environment variables use the ROSLYN_LENS_ prefix.

Variable	Type	Default	Description
ROSLYN_LENS_TIMEOUT_SECONDS	int	30	Maximum time (seconds) for any Roslyn operation before timeout
ROSLYN_LENS_MAX_RESULTS	int	100	Maximum number of results returned per query
ROSLYN_LENS_CACHE_SIZE	int	20	Number of project compilations kept in the LRU cache
ROSLYN_LENS_LOG_LEVEL	string	Information	Log verbosity: Trace, Debug, Information, Warning, Error
ROSLYN_LENS_SOLUTION	string	(unset)	Path to a .sln/.slnx (or a directory to search). Used when no --solution argument is given; blank falls through to auto-discovery

Setting env vars in .mcp.json

{
  "mcpServers": {
    "roslyn-lens": {
      "type": "stdio",
      "command": "roslyn-lens",
      "args": [],
      "env": {
        "ROSLYN_LENS_TIMEOUT_SECONDS": "60",
        "ROSLYN_LENS_CACHE_SIZE": "100",
        "ROSLYN_LENS_LOG_LEVEL": "Debug"
      }
    }
  }
}

Setting env vars via Claude Code CLI

claude mcp add --scope user --transport stdio \
  -e ROSLYN_LENS_TIMEOUT_SECONDS=60 \
  -e ROSLYN_LENS_CACHE_SIZE=100 \
  roslyn-lens -- roslyn-lens

CLI arguments

Argument	Short	Description
--solution <path>	-s	Explicit path to .sln or .slnx file

Solutions are resolved in this order: the --solution argument, then the ROSLYN_LENS_SOLUTION environment variable, then BFS auto-discovery from the current working directory (max 3 levels up). Auto-discovery prefers .slnx over .sln. The environment variable is what the Claude Desktop bundle uses to inject the solution chosen in its settings UI.

Skipped directories during auto-discovery

.git, .vs, .idea, node_modules, bin, obj, packages, artifacts, TestResults, .claude, nupkgs

Tuning guide

Small solutions (< 10 projects)

Default settings work well. All compilations are warmed at startup.

Medium solutions (10-50 projects)

Defaults are fine. Compilations are lazy-loaded on first access.

Large solutions (50+ projects)

ROSLYN_LENS_CACHE_SIZE=100
ROSLYN_LENS_TIMEOUT_SECONDS=60

Increase cache size to avoid recompilation churn. Increase timeout for initial compilation of large projects.

Monorepos with multiple solutions

Specify the solution explicitly:

roslyn-lens --solution ./src/Backend/Backend.slnx

Or let auto-discovery find all solutions and switch at runtime:

> "List available solutions"     → calls list_solutions
> "Switch to Frontend.slnx"     → calls switch_solution

See Solution Management Tools.

Logging

All logs go to stderr (stdout is reserved for MCP JSON-RPC).

# Debug logging to a file
ROSLYN_LENS_LOG_LEVEL=Debug roslyn-lens 2>/tmp/roslyn-lens.log

Log levels:

• Trace: All Roslyn operations, cache hits/misses
• Debug: Symbol resolution, file watcher events
• Information: Startup, solution loading, tool execution
• Warning: Missing projects, failed compilations
• Error: Unrecoverable failures