FsLangMCP

About Tool Dependencies

dotnet tool packages cannot automatically install other global tools during installation. fslangmcp --bootstrap-tools runs dotnet tool update -g (or install if missing) for:

• fsautocomplete
• ionide.projinfo.tool

To install them manually instead:

dotnet tool install -g fsautocomplete
dotnet tool install -g ionide.projinfo.tool

Quickstart

Prerequisites: .NET SDK 10+ on PATH.

dotnet tool install -g FsLangMcp
fslangmcp --bootstrap-tools   # one-time: fetches fsautocomplete + ionide.projinfo.tool

Add to your MCP client config:

{
  "mcpServers": {
    "fslangmcp": { "command": "fslangmcp" }
  }
}

Then call set_project with your .fsproj or .sln path, and start with find or check.

Full setup: docs/getting-started.md · Per-client configs: docs/configuration.md · Runnable examples: examples/.

Example Agent Session

1. set_project  {"projectPath": "/abs/path/MyApp.sln"}
   → readiness.lsp=true, loadedProjects=[...], fslangmcpVersion="0.12.1"

2. check  {}
   → verdict="clean"

3. find  {"query": "OrderId", "kind": "definition"}
   → [Domain/Order.fs:12 definition `type OrderId = ...`, ...]

4. fcs_file_outline  {"path": "/abs/path/Domain/Order.fs"}
   → module/type headers, memberCounts by kind

5. fcs_rename_preview  {"path": "/abs/path/Domain/Order.fs", "line": 12, "character": 5, "newName": "OrderIdentifier"}
   → edits grouped by file, totalEdits=7, crossProject=false

Parallel Agent Usage

Pass projectPath explicitly on every FCS tool call — FCS tools cache project-wide results per resolved .fsproj, so agents targeting different projects share no stale caches.

{ "path": "/absolute/path/to/File.fs", "projectPath": "/absolute/path/to/App.fsproj" }

Concurrency limits (env-overridable):

• FSLANGMCP_MAX_CONCURRENT_FCS=2
• FSLANGMCP_MAX_CONCURRENT_LSP=1 (LSP tools serialize to protect FSAC workspace state)

Runtime Options

Command-line args:

• --project <path> / -p <path> — pre-load a project on startup
• --fsac-command <cmd> — override the fsautocomplete executable
• --fsac-args "<args>" — pass extra args to FSAC
• --bootstrap-tools — install/update fsautocomplete + ionide.projinfo.tool

Environment fallbacks: FSAC_COMMAND, FSAC_ARGS, FSA_PROJECT_PATH.

MCP Stdio Config

Installed tool:

{
  "mcpServers": {
    "fsharp": {
      "command": "fslangmcp",
      "args": ["--project", "/absolute/path/to/App.fsproj"]
    }
  }
}

Local dev (without install):

{
  "mcpServers": {
    "fsharp": {
      "command": "dotnet",
      "args": [
        "run", "--project", "/path/to/FsLangMcp.fsproj",
        "--", "--project", "/absolute/path/to/App.fsproj"
      ]
    }
  }
}