Claude Desktop

Give Claude the rules tools through MCP. Runs locally; nothing leaves your machine.

Before you start

Finish Installation first. make doctor should pass. The server uses the same database and embedder as make search, so Docker Desktop and Ollama must be running whenever Claude Desktop is.

Add the server

In Claude Desktop, open Settings, Developer, Edit Config. Add this to claude_desktop_config.json, then save.

Windows, with the project inside WSL (Ubuntu):

{
  "mcpServers": {
    "rb-errata": {
      "command": "wsl.exe",
      "args": ["-e", "bash", "-lc",
               "cd ~/RB_Errata && exec uv run --frozen python -m rb_errata.server"]
    }
  }
}

bash -lc starts a login shell, so uv is on the path just as it is in your terminal. If you cloned the project somewhere other than your WSL home folder, change ~/RB_Errata. If Ubuntu is not your default WSL distribution, put "-d", "Ubuntu", before "-e".

macOS or Linux:

{
  "mcpServers": {
    "rb-errata": {
      "command": "bash",
      "args": ["-lc",
               "cd ~/RB_Errata && exec uv run --frozen python -m rb_errata.server"]
    }
  }
}

Check it works

Quit Claude Desktop fully (from the tray icon on Windows) and open it again. The tools menu should list rb-errata with five tools: search_rules, ask, get_rule, list_versions and what_changed.

Ask: "As of 1 May 2026, does a spell that gets countered count as played for Legion? Use rb-errata." Claude should search with as_of 2026-05-01, cite v1.3 rules and answer yes: v1.3 made Legion check whether another card was Finalized, and Riot's Unleashed FAQ confirmed a countered spell still counts. Ask the same question as of 1 February 2026 and the answer is no.

If a tool fails

Every error says what to do:

• database unreachable: start Docker Desktop, then make db-up.
• Ollama unreachable: start Ollama.
• embedder check failed: the embedding model changed; run make doctor.
• the database differs from data/corpus.json: run make ingest.
• data/raw/... is missing: run make fetch. get_rule and what_changed read the rules PDFs.

To see the server on its own, run make mcp in the project folder. It waits silently for a client; Ctrl+C stops it.

Local only

Claude Desktop starts the server on your machine over stdio. It opens no network port. Rule text goes from your machine to Claude Desktop only, the same as pasting it yourself.

How good is it?

make mcp-check starts the server the way Claude Desktop does and asks it every question in the question set. It checks the answers match the measured run on the Results page.