# Music Theory Chord Speller

> Music Theory Chord Speller is a paid API for AI agents from music-theory.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-30).

Spells a chord from its symbol (e.g. Cmaj7, F#m7b5, Dsus4, C/E) returning notes, intervals, semitones from root, and MIDI numbers.

## Facts

- Endpoint: GET https://music-theory.x402tookit.com/chord?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-30
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/music-theory-chord-speller-384b7411
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_DDT0bBdKdNOySseXpK2Ve

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-chord-speller-384b7411
```

Example prompt: What notes, intervals, and MIDI numbers make up an F#m7b5 chord? Give me the full music theory breakdown.

## When to prefer this

Use this endpoint when you need a programmatic, structured breakdown of a chord from its symbol — including exact note names, interval qualities, semitone distances, and MIDI numbers. Prefer it over scale or key endpoints when the user asks specifically about chord spelling, voicing, or MIDI note content. It handles slash chords (inversions), suspended chords, added-note chords, and complex jazz extensions like m7b5 and 7b9.

## Known failure modes

- Unrecognized or malformed chord symbol returns error reasons array explaining what could not be parsed
- Highly ambiguous or non-standard chord symbols may yield degraded:true with best-effort results
- Missing 'symbol' query parameter returns a validation error
- Extremely unusual extensions or alterations not in the chord library may not resolve correctly

## How this service works

Spell a chord from its symbol (Cmaj7, F#m7b5, G7b9, Dsus4, C/E): notes, intervals, semitones and MIDI numbers.

## Output

Returns a structured object with the chord symbol, root note, bass note, quality, inversion, array of note names (e.g. ['C','E','G','B']), interval names (e.g. ['P1','M3','P5','M7']), semitones from root (e.g. [0,4,7,11]), MIDI numbers at octave 4, and any chord modifications. Also includes a summary string and degraded/error 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": [
      "symbol"
     ],
     "properties": {
      "symbol": {
       "type": "string",
       "description": "Chord symbol: C, Am7, Bbmaj7, F#m7b5, G7b9, Cadd9, Dsus4, C/E"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "bass": {},
      "root": {
       "type": [
        "null",
        "string"
       ]
      },
      "notes": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "symbol": {
       "type": [
        "null",
        "string"
       ]
      },
      "quality": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "intervals": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "inversion": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "notChecked": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "modifications": {
       "type": [
        "array",
        "null"
       ]
      },
      "midiRootOctave4": {
       "type": [
        "array",
        "null"
       ],
       "it
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/music-theory-chord-speller-384b7411/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)