Getting started

mcpFortyTwo speaks the Model Context Protocol over Streamable HTTP at /mcp. Any MCP-capable client that supports the http transport can connect — there is nothing to install on the client side.

Pick a server

Hosted
Local

A public instance runs at https://mcp42.jackjakarta.xyz/mcp. Use this if you just want to try it out — no setup required.

Run mcpFortyTwo on your machine — see Configuration for the full setup, then start it with pnpm dev. The MCP endpoint is http://localhost:3000/mcp.

Add it to your MCP client

The config shape is identical across Claude Desktop, Claude Code, and most other MCP-capable clients.

{
  "mcpServers": {
    "mcpFortyTwo": {
      "type": "http",
      "url": "https://mcp42.jackjakarta.xyz/mcp"
    }
  }
}

Swap the URL for http://localhost:3000/mcp if you are running locally. Reload your client and confirm the tools show up — in Claude Code, run /mcp to list connected servers and their tool counts.

Call your first tool

Ask your client to spell a chord — it should pick get-chord automatically. The structured result looks like:

{
  "root": "C",
  "quality": "Major Seventh",
  "notes": ["C", "E", "G", "B"],
  "intervals": ["1P", "3M", "5P", "7M"],
  "extensions": ["7M"]
}

Every tool returns both a human-readable text content block (for the model to render) and a typed structuredContent payload (for downstream tools to consume).

For MIDI tools like generate-progression-midi, the structuredContent includes a base64 midi field — pipe it through base64 -d > out.mid to play it back in any DAW.

Health check

curl https://mcp42.jackjakarta.xyz/health
# → {"ok":true}

Useful for uptime monitors, deployment probes, or confirming a local instance is up before you point a client at it.