Music21 Composer

You run Music21 Composer MCP to generate, transform, and realize musical ideas programmatically through a dedicated API server. It focuses on composing workflows, enabling constraint-based melody generation, phrase transformations, reharmonization, counterpoint, chord realization, and MIDI export, all from a lightweight HTTP interface.

How to use

Start the MCP HTTP server to expose a stable API you can call from your music tooling or custom clients.

Your typical workflow is to start the server, then use the exposed endpoints to generate melodies, apply transformations, reharmonize progressions, add voices, realize chords, and export MIDI. You can initiate HTTP requests to the server’s endpoints and supply musical data in supported formats to obtain the desired output.

How to install

Prerequisites you need on your system: Python 3.8+ and a working Python package manager.

Clone and install the MCP package with development dependencies enabled.

git clone <repo-url>
cd music21-composer-mcp

pip install -e ".[dev]"

Run the server and use the API

Launch the HTTP server on a port of your choice. The server binds to an HTTP endpoint you can reach from clients.

composer-mcp --mode http --port 8000

Interact with the API

Once the server is running, you can send requests to perform music generation and export tasks. For example, export a MIDI file based on a simple note sequence.

POST http://localhost:8000/export_midi
Content-Type: application/json

{"stream": "C4, D4, E4, G4", "tempo": 120}

Available tools

generate_melody

Constraint-based melody generation to produce melodies that satisfy given musical constraints.

transform_phrase

Apply musical transformations such as sequence, inversion, retrograde, and other phrase-level edits.

reharmonize

Generate alternative chord progressions to explore harmonic options.

add_voice

Counterpoint and voice generation to create multiple independent lines.

realize_chord

Convert chord symbols into voiced piano/ensemble arrangements.

export_midi

Export generated music to the MIDI format for playback and further processing.