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Music Theory Key Signature Lookup
x402
Music Theory Key Signature Lookup is a paid API for AI agents from music-theory.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-11-03).
Returns key signature details (sharps/flats, accidentals), circle-of-fifths position and neighbours, and relative/parallel keys for any major or minor key.
Price / call$0.02
Success—
StatusUnknown
How this service works
Key signature (sharps or flats), circle-of-fifths neighbours, relative and parallel keys for any major or minor key.
Output
A JSON object containing: the key signature type (sharp or flat), count of accidentals, list of accidental note names, whether it is a theoretical key, all scale notes, the relative key, parallel key, dominant key, subdominant key, enharmonic equivalent key, the key's position on the circle of fifths (clock position and fifths index), and the full circle-of-fifths array with clock positions and accidental counts for each key.
Example use cases
Composing in a new key
“I'm writing a piece in Bb major — can you tell me its key signature, which accidentals it uses, and what its relative minor and circle-of-fifths neighbours are?”
Music theory homework help
“For my theory class I need to know everything about the key of D minor: how many flats it has, its relative major, parallel major, dominant and subdominant keys, and where it sits on the circle of fifths.”
Transposing song to a related key
“I'm thinking of moving a song from E major to a nearby key — can you show me E major's circle-of-fifths neighbours, its relative minor, and its key signature so I can decide where to go?”
Technical details
Endpoint
GEThttps://music-theory.x402tookit.com/key-signature?utm_source=zero.xyzWhen to prefer
Use this endpoint when you need authoritative, structured key signature data for any standard or theoretical major/minor key, including accidentals, circle-of-fifths relationships, and relative/parallel key lookups — especially when building music theory tools, educational apps, or composition assistants that need reliable harmonic context rather than generating that information from an LLM.
Side effects
- Missing 'key' query parameter returns an error
- Unrecognized key name or format returns null/error fields
- Ambiguous key names without major/minor qualifier may default to major
- Theoretical keys (e.g. G# major) may be flagged with a 'theoretical' flag rather than rejected
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Tags
x402
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