Sonic Pi MCP

Model Context Protocol (MCP) server for Sonic Pi. Describe music in natural language in your LLM client; the model generates Sonic Pi code and this server sends it over OSC. Use the included queue runner in Sonic Pi for crossfades between segments.

Features

• queue_segment — send the next full musical segment (named live_loops, use_bpm, etc.).
• run_code — same as queue_segment (compatibility).
• stop_all — hard stop via OSC (/stop-all-jobs), like Sonic Pi’s Stop.
• play_note — quick test note.
• Resource — DJ session craft, vocabulary, and tool usage (read from the MCP client).
• Prompt next_performance_segment — help frame the next block for longer sets.
• Env — OSC_HOST, OSC_PORT, OSC_CODE_PATH, OSC_STOP_ALL_PATH.

Prerequisites

• Sonic Pi v4.x
• Node.js 18+ (npx / node)
• An MCP-capable client (Cursor, Claude Desktop, VS Code with MCP, etc.)

Optional: Bun for local development (bun run dev).

One-time Sonic Pi setup (queue runner)

1. Open Sonic Pi.
2. Copy sonic-pi-queue.rb into a buffer.
3. Press Run and leave it running.

The buffer listens on the default OSC port and crossfades between segments sent by the MCP.

Install the MCP server

npx -y sonic-pi-mcp

Point your client at this command over stdio (see below).

Cursor

Use ~/.cursor/mcp.json and/or .cursor/mcp.json in a project:

{
  "mcpServers": {
    "sonic_pi_mcp": {
      "command": "npx",
      "args": ["-y", "sonic-pi-mcp"]
    }
  }
}

Local clone (after npm install or bun install and bun run build):

{
  "mcpServers": {
    "sonic_pi_mcp": {
      "command": "node",
      "args": ["/absolute/path/to/sonic-pi-mcp/bin/cli.mjs"]
    }
  }
}

Bun without building — some clients ignore cwd; use an absolute path to src/server.ts, or use the launcher:

{
  "mcpServers": {
    "sonic_pi_mcp": {
      "command": "/absolute/path/to/sonic-pi-mcp/bin/mcp-dev.sh",
      "args": []
    }
  }
}

Run chmod +x bin/mcp-dev.sh once. The script changes into the repo and runs bun run src/server.ts.

Claude Desktop

~/Library/Application Support/Claude/claude_desktop_config.json (paths differ on Windows):

{
  "mcpServers": {
    "sonic_pi_mcp": {
      "command": "npx",
      "args": ["-y", "sonic-pi-mcp"]
    }
  }
}

For a local clone, prefer bin/mcp-dev.sh (see above) if you see Module not found "src/server.ts" or spawn bunx ENOENT. Remove and re-add the MCP in the app if an old definition is cached.

VS Code

Configure your MCP extension to run npx with -y and sonic-pi-mcp, stdio transport, per the extension’s docs.

Environment variables

Variable	Default	Meaning
OSC_HOST	127.0.0.1	Sonic Pi host
OSC_PORT	4560	Sonic Pi OSC port
OSC_CODE_PATH	/run-code	OSC path for code (must match your Sonic Pi buffer)
OSC_STOP_ALL_PATH	/stop-all-jobs	Hard stop path

Allow incoming OSC in Sonic Pi if you connect from another machine; set OSC_HOST accordingly.

Development

git clone https://github.com/abhishekjairath/sonic-pi-mcp.git
cd sonic-pi-mcp
bun install   # or npm install
bun run build
bun run dev

OSC smoke test (Sonic Pi + runner running):

bun run test

MCP Inspector

npx @modelcontextprotocol/inspector

Use node with argument bin/cli.mjs and this directory as the working directory (after bun run build).

Troubleshooting

• No sound — Sonic Pi open? Queue buffer running? Port 4560 reachable?
• Nothing happens — OSC enabled in Sonic Pi; OSC_HOST / OSC_PORT match.
• Layers pile up — Use queue_segment with named live_loops; use stop_all only for a full reset.
• Module not found "src/server.ts" (Claude) — Use bin/mcp-dev.sh as command with empty args, or absolute paths; don’t rely on cwd alone.
• resources/list / prompts/list → Method not found — You’re on an older build that only exposed tools. Reinstall/restart the MCP from this repo or npm so resources and prompts are registered.
• Ruby errors in Sonic Pi log — The generated code failed to parse or run; fix the snippet (brackets, samples, syntax) and send again. The queue runner prints a code snippet on failure.

License

MIT — see LICENSE.