Show HN: RiffMCP is an MCP server that lets LLMs compose, play, and render music

2 points

10 months ago

I wanted to find out how good LLMs are at composing music, being that language models are not explicitly trained to do so.

RiffMCP is an MCP server that makes that possible by providing any LLM with a tool for playing and engraving music.

How did they do? The demo video shows music composed by Opus 4.1, Gemini 2.5 and GPT 5 for comparison.

It’s a local server that runs as a native app on macOS. This means that using included prompts it can also work with LLMs that don’t yet support MCP. For example to test GPT 5, I prompted it to compose music and output RiffMCP’s format, then copy/pasted the result into the app to hear it playback and see the sheet music.

It’s mostly experimental so far, but I may consider improvements like driving external midi. Full code provided under Apache 2.0 license.

Feedback appreciated, contributions welcome.

Watch demo:

https://youtu.be/Ksfw34dtIro?si=c3MERdxm9dhAwXiv

Code:

https://github.com/whitneyland/riffmcp

Try it out:

https://whitneyland.github.io/riffmcp

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