MIDI note converter API

Converts between a MIDI note number (0–127) and a note name and frequency in both directions, with pitch class, octave and enharmonic spelling. Answers 'What note is MIDI 69?', 'What is the MIDI number of A4?'.

Price$0.02per request

MethodPOST

Route/v1/music/midi-note

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

musicmidinotefrequencypitch-classoctaveenharmonicconverteraudio

API URLhttps://x402.hexl.dev/v1/music/midi-note

Integration docs

Example request

{
  "midi": 69
}

Example response

{
  "midi": 69,
  "noteName": "A4",
  "pitchClass": 9,
  "pitchClassName": "A",
  "octave": 4,
  "frequency": 440,
  "a4Reference": 440,
  "enharmonic": null
}

Input schema

{
  "type": "object",
  "properties": {
    "midi": {
      "type": "number",
      "examples": [
        69,
        60
      ]
    },
    "note": {
      "type": "string",
      "examples": [
        "A4"
      ]
    },
    "a4": {
      "type": "number",
      "examples": [
        440
      ]
    },
    "preferFlats": {
      "type": "boolean"
    }
  }
}

Output schema

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