Parse a chord symbol into its root, quality, intervals, extensions, and harmonic function. When a key is provided, returns the Roman numeral, scale degree, and whether the chord is diatonic.

Resolve a chord symbol to spelled note names, frequencies in Hz, MIDI numbers, and recommended improvisation scales.

Generate instrument-ready voicings for a chord in a specified style. Pass previousNotes (or a previousVoicing object) from an earlier result to get a voiceLeadingScore for the transition. Styles: rootless, bill_evans, shell, triad, pad, guide-tones, guide-tone-1, guide-tone-2, both-guide-tones, drop-2, drop-3.

Reharmonize a chord progression using jazz techniques. Returns one alternative per applicable technique, each with the new progression, the changes, and a plain-English explanation. With technique 'auto' (default) it returns every technique that applies. Techniques: tritone_sub, ii_v_insertion, modal_interchange, diminished_passing, secondary_dominant, chain_of_dominants, coltrane_changes, backdoor. (modal_interchange and backdoor require a key.)