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Music Theory – Chord Progression Transposer
x402
Music Theory – Chord Progression Transposer is a paid API for AI agents from music-theory.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).
Transposes a chord progression by a given number of semitones or between two keys, returning correctly spelled output chords for the target key.
Price / call$0.02
Success—
StatusUnknown
How this service works
Transpose a chord progression by semitones or from one key to another, with spelling that fits the target key.
Output
Returns a list of transposed chord names (one per input chord), the detected or specified source key, the target key, the semitone distance applied, a summary string, and per-chord input-to-output mappings. May also include spelling rationale and a disclaimer if any chords could not be resolved.
Example use cases
Singer's key adjustment
“The song is in C major with chords C Am F G, but my vocalist needs it 3 semitones higher — can you transpose the whole progression for me?”
Jazz chart transposition for horn
“I've got a jazz progression Cmaj7 Am7 Dm7 G7 written for piano in C. Can you transpose it to Bb major so a tenor sax player can read it in concert pitch?”
Capo-friendly guitar key change
“I want to play Am G F E on guitar but my capo is on fret 2 — what does the progression become if I shift everything down 2 semitones, spelled with flats?”
Technical details
Endpoint
GEThttps://music-theory.x402tookit.com/transpose?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need to move an entire chord progression to a new key with musically correct chord spelling — e.g. Bb instead of A# in flat keys. Prefer it over manual interval arithmetic when key context matters for enharmonic spelling correctness. Ideal for song arrangement, vocal range matching, instrument transposition, and capo calculations.
Side effects
- Missing required 'progression' parameter returns an error
- Ambiguous or unrecognised chord symbols may result in null output entries or a 'notChecked' list
- Providing both 'semitones' and 'fromKey'/'toKey' may cause conflict; only one method should be used
- Out-of-range semitone values (beyond ±24) are rejected
- Misspelled key names (e.g. 'Csharp' instead of 'C#') may fail to parse
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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