Relative, parallel and circle keys API

Finds a key's relative, parallel, dominant and subdominant keys and its position on the circle of fifths — the harmonic neighbourhood used for modulation. Answers 'What is the relative minor of C major?', 'Where is C on the circle of fifths?'.

Price$0.04per request

MethodPOST

Route/v1/music/related-keys

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

musiccircle-of-fifthsrelative-keyparallel-keymodulationtheoryharmonykeynotation

API URLhttps://x402.hexl.dev/v1/music/related-keys

Integration docs

Example request

{
  "key": "C",
  "mode": "major"
}

Example response

{
  "key": "C major",
  "relativeKey": "A minor",
  "parallelKey": "C minor",
  "dominantKey": "G major",
  "subdominantKey": "F major",
  "circleOfFifthsPosition": 0,
  "clockPosition": 0,
  "accidentalCount": 0
}

Input schema

{
  "type": "object",
  "required": [
    "key"
  ],
  "properties": {
    "key": {
      "type": "string",
      "examples": [
        "C",
        "A"
      ]
    },
    "mode": {
      "type": "string",
      "examples": [
        "major",
        "minor"
      ]
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}