PyTheory + Claude Code

PyTheory ships an official Claude Code plugin, so you can make and analyze music just by talking to Claude. Ask in plain language and Claude writes and runs PyTheory for you — composing arrangements, working out chord voicings, naming the key of a melody, building guitar fingerings, or transcribing a recording.

Install

In Claude Code, add the marketplace and install the plugin:

/plugin marketplace add kennethreitz/pytheory-skill
/plugin install composing-with-pytheory@pytheory

That one plugin bundles six skills (below) — installing it gives Claude all of them. You also need PyTheory itself available wherever Claude runs (prefer uv if you have it):

uv pip install pytheory      # or: pip install pytheory

Then just talk to it

Each skill triggers on its own kind of request, so you don’t pick one — you just ask:

  • “Write me a bossa nova in G minor and save the MIDI.”

  • “Make a four-chord lo-fi loop and let me hear it.”

  • “What’s the fingering for F#m7b5? And show me a DADGAD Cmaj7.”

  • “Tune my guitar to drop D.”

  • “What key are C E G B D in, and what chord comes after G?”

  • “Voice-lead Cmaj7 to Fmaj7 and give me the tritone sub of G7.”

  • “Turn this hum into MIDI and a guitar lead sheet.”

Claude composes, plays, analyzes, and exports — to WAV, MIDI, MusicXML, LilyPond, ABC, or guitar tab — all from the same PyTheory you’d use in a script.

Heard in the wild

Interpretations is a full 24-track album composed entirely in PyTheory — Indian ragas colliding with trap beats, singing bowls ringing over 808 sub bass, microtonal shruti tunings, a string quartet ambushed by drum & bass. Every sound is generated from code: each track is a .py file, with no samples and no DAW. It’s a real, published example of where this code-first workflow can go.

Listen on Apple Music, Spotify, or the web player — and read the source (every track as Python you can run) at https://github.com/kennethreitz/interpretations.

The skills

Skill

What it does

composing-with-pytheory

Full arrangements — progressions, melodies, basslines, drums, layering — rendered to audio or MIDI, with PyTheory’s house style baked in.

playing-guitar-with-pytheory

Fingerings, chord shapes and tab, chord identification, scale diagrams, alternate tunings and capo, ~20 stringed instruments, Nashville charts, and the real-time tuner.

chord-lab-with-pytheory

A single chord’s notes, voicings (inversions, drop-2/3, open), tension, tritone substitution, and voice leading.

keys-and-harmony-with-pytheory

Keys and progressions — diatonic chords, Roman-numeral analysis, key detection, secondary dominants, borrowed chords, and modulation.

scales-modes-and-tunings-with-pytheory

Scales and modes, “what scale fits these notes?”, intervals, overtones, the circle of fifths, and 16 tuning systems.

transcription-and-notation-with-pytheory

Audio → notes/MIDI, chord recognition, MIDI import, and export to MusicXML / LilyPond lead sheets / ABC / tab.

How it works

A skill is a set of instructions Claude reads on demand. These skills teach Claude PyTheory’s API — and its taste (subtle detune, gentle humanization, sensible voices) — so the music it writes is intentional, not random. Claude then writes and runs ordinary PyTheory Python on your machine; nothing is sent anywhere, and the files it produces are yours.

The plugin is open source and generated from the PyTheory repo: https://github.com/kennethreitz/pytheory-skill