Music21 Composer MCP

A composition-focused MCP server built on music21, designed for generative workflows.

Features

• generate_melody - Constraint-based melody generation
• transform_phrase - Musical transformations (sequence, inversion, retrograde, etc.)
• reharmonize - Generate alternative chord progressions
• add_voice - Counterpoint and voice generation
• realize_chord - Chord symbol to voicing
• export_midi - Export to MIDI format

Installation

# Clone the repository
git clone <repo-url>
cd music21-composer-mcp

# Install with dev dependencies
pip install -e ".[dev]"

Quick Start

Start the HTTP server

composer-mcp --mode http --port 8000

API Usage

# Export notes to MIDI
curl -X POST http://localhost:8000/export_midi \
  -H "Content-Type: application/json" \
  -d '{"stream": "C4, D4, E4, G4", "tempo": 120}'

API Documentation

With the server running, visit http://localhost:8000/docs for interactive API documentation.

Input Formats

The API accepts three input formats:

1. Note List (simplest)

C4, D4, E4, G4           # Quarter notes (default)
C4:h, D4:q, E4:e         # With durations (h=half, q=quarter, e=eighth)
C#4:qd, Bb3:h            # Accidentals and dotted notes

2. ABC Notation

X:1
M:4/4
K:C
CDEF|GABc|

3. MusicXML

Standard MusicXML format.

Development

# Run tests
pytest

# Run with coverage
pytest --cov=composer_mcp

# Format code
black src tests
ruff check src tests

Implementation Status

License

MIT