RiffMCP

RiffMCP is an MCP server that allows LLMs to play, compose, and render music.

Overview

Local MCP server that runs as a native macOS app
Uses MCP stdio protocol which is routed to a built-in HTTP server
Defines a JSON-based music sequence format used between the LLM and the MCP server
Multi-track music is played back using a high quality soundfont
Supports basic sheet music rendering

Add RiffMCP to Claude Desktop, Gemini CLI, or any LLM that supports MCP servers (see Setup below).
Once configured, you can chat with the LLM to generate music or view the rendered output.

In addition to MCP functionality, I wanted an interface that allows monitoring MCP activity, a simple JSON editor for experimentation, and a piano roll to see how playback is working.
The challenge became how to implement MCP stdio protocol, an HTTP server, and a GUI simultaneously without any Node.js/Electron dependencies or separate daemon processes. The goal is to have only one native app running.
The solution was to use a smart app / proxy mode architecture.

Add to Claude Desktop configuration: Add this to your Claude Desktop app configuration file:

Location: ~/Library/Application Support/Claude/claude_desktop_config.json

Create or extend the top-level "mcpServers" object:

{
  "mcpServers": {
    "riff": {
      "command": "/Applications/RiffMCP.app/Contents/MacOS/RiffMCP",
      "args": ["--stdio"]
    }
  }
}

Create or extend the top-level "mcpServers" object:

{
  "mcpServers": {
    "riff": {
      "command": "/Applications/RiffMCP.app/Contents/MacOS/RiffMCP",
      "args": ["--stdio"]
    }
  }
}

Sheet music rendering uses the powerful Verovio engine, but not all features are implemented. Still needs triplets, multi-page output, etc.
Web server is a minimal hand-rolled implementation. swift-nio may be added as a more scalable/robust component.