Write chords with Claude

Ask for chords

Where /ck-chordsCopy in the Claude panel

You need the same things as for every Claude feature in CodaKeys: a Mac with Apple silicon on macOS 13 or later, and Claude Code signed in with your own Claude plan (the free plan does not include Claude Code). The Guide covers the install. CodaKeys is an invitation-only beta, free while it lasts.

Type /ck-chordsCopy and what you want, such as “a sad verse in A minor” or “lift the last chorus”. You can also say it in your own words and Claude works the same way. Naming a section helps: Claude writes the chords for that part and leaves the rest of the track alone.

If a melody is already in the song, highlight the bars you want chords for first. Claude then sees exactly those notes, which is what the chords must fit.

What Claude does first

Claude reads the song before it writes: the key, any chords that exist, the sections, and what the bass and melody are playing. Then it tells you the progression in plain chord symbols with one line on why, for example “verse Am–F–C–G, because it is the familiar sad shape; the chorus lifts to F–G–Am”.

It starts from a well-worn shape close to what you asked for and adds one surprise per section, such as a borrowed minor four chord, rather than wandering. If you describe a feeling (“sadder”, “dreamier”), it names the device it used for it, so you learn what to ask for next time.

Chords for a melody you have

If you have a melody and no chords, Claude offers three progressions that fit it: a plain set, one with borrowed chords, and one with sevenths. They arrive as versions on the chord track that you flip between while the song plays, and you keep the one you like. The hum-to-MIDI article ends this way: hum a tune, then ask for chords under it.

Claude checks that the melody note on each beat is part of the new chord, or a deliberate tension that resolves by a step. A chord that fights the tune is a bug; tell Claude which bar and it fixes it.

What you get back

The chords are real notes on an instrument track. Open the track and you can move, shorten or delete any note like one you played yourself. Claude writes them the way a chart reads: seventh and ninth chords, slash chords such as C/E (which puts E in the bass), and inversions so the notes move by small steps from one chord to the next.

When Claude changes chords that already play, your version stays as it was. Claude’s goes in as a second version of the track: A is yours, B is Claude’s. The letter button on the track’s header, or Track › Track Alternatives › Next Alternative, switches between them. Choose Keep This Alternative or Drop This Alternative in that menu when you have decided.

Listen, change, undo

Loop the section and play it. Then say what you hear, in your own words:

• “Make it sadder” or “jazzier”: Claude picks a device and explains it.
• “Too busy”: fewer chord changes, or plainer chords without the ninths and elevenths.
• “The bass should walk”: Claude uses inversions so the bass line moves instead of repeating the root.
• Anything you would rather do by hand: open the track and change the notes.

Anything Claude changes can be undone with ⌘Z like your own edits. If you want a save-point that outlasts the session before a bold change, ask for /ck-checkpointCopy first.

New chords usually want new partners. Claude offers a matching bassline or melody next, and /ck-abCopy builds two or three chord versions to compare by ear if you cannot decide.

Then what

Asking why a progression works is allowed: /ck-theoryCopy names the key and chords in a song and explains them. Not signed up yet? Ask for the beta on the home page. The rest of what CodaKeys does is on Features.