# Music Theory Note-to-Frequency Converter

> Music Theory Note-to-Frequency Converter 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).

Converts a note name (e.g. C#4, Bb3) or MIDI number to its MIDI value, frequency in Hz, and wavelength in cm, with an adjustable A4 reference pitch.

## Facts

- Endpoint: GET https://music-theory.x402tookit.com/note-freq?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/music-theory-note-to-frequency-converter-3caa6314
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_NFKDtYiQ6E25xYuqSa8ln

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability music-theory-note-to-frequency-converter-3caa6314
```

Example prompt: What is the frequency in Hz and MIDI number for C#4, using a 432 Hz A4 reference pitch?

## When to prefer this

Use this endpoint when you need to convert a note name or MIDI number to its exact frequency, MIDI value, and wavelength — especially when non-standard tuning (baroque 415, Verdi 432, custom A4) is required. Prefer this over generic music APIs when precise acoustic properties and enharmonic spellings are needed for a specific note.

## Known failure modes

- Invalid note name format (e.g. missing octave number) returns an error
- MIDI number outside 0–127 range is rejected
- A4 reference pitch outside 400–480 Hz range is invalid
- Malformed query parameter causes a bad request response
- Missing required 'note' parameter returns an error

## How this service works

Note name (C#4, Bb3) or MIDI number to MIDI, frequency in Hz and wavelength, with adjustable A4 reference pitch.

## Output

Returns the note name, MIDI number, pitch class, frequency in Hz, wavelength in cm, enharmonic equivalents, the A4 reference Hz used, and the octave convention, along with a summary and optional degraded/disclaimer flags.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "note"
     ],
     "properties": {
      "a4": {
       "type": "number",
       "description": "Reference pitch for A4 in Hz, 400 to 480 (default 440; baroque 415, Verdi 432)"
      },
      "note": {
       "type": "string",
       "description": "Note name with octave (A4, C#5, Eb3) or a MIDI number 0 to 127"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "a4Hz": {
       "type": [
        "null",
        "number"
       ]
      },
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "midi": {
       "type": [
        "null",
        "number"
       ]
      },
      "note": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "pitchClass": {
       "type": [
        "null",
        "number"
       ]
      },
      "frequencyHz": {
       "type": [
        "null",
        "number"
       ]
      },
      "wavelengthCm": {
       "type": [
        "null",
        "number"
       ]
      },
      "wavelengthNote": {
       "type": [
        "null",
        "string"
       ]
      },
      "enharmonicNames": {
       "type": [
        "array",
  
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/music-theory-note-to-frequency-converter-3caa6314/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from music-theory.x402tookit.com](https://www.zero.xyz/host/music-theory.x402tookit.com/llms.txt)