# Music Theory Roman Numeral Analysis

> Music Theory Roman Numeral Analysis 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).

Analyzes a chord progression in a given key and returns Roman numeral notation including inversions, borrowed chords, and secondary dominants.

## Facts

- Endpoint: GET https://music-theory.x402tookit.com/roman-numerals?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-roman-numeral-analysis-2b20166b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_XpSMBxbhBR5tH3IDh9blk

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-roman-numeral-analysis-2b20166b
```

Example prompt: Can you do a Roman numeral analysis of the progression C Am F G7 in the key of C major — I want to know if any chords are borrowed or act as secondary dominants?

## When to prefer this

Use this endpoint when you need structured Roman numeral harmonic analysis of a chord progression in a specific key, including identification of inversions, borrowed chords, and secondary dominants. Prefer this over manual analysis or general music info APIs when you need machine-readable harmonic function labels for each chord.

## Known failure modes

- Unrecognized chord symbol returns it in 'notChecked' array with partial results
- Invalid or ambiguous key string may return null key or degraded analysis
- Chords with complex extensions may not be fully analyzed
- Missing required 'key' or 'progression' query parameter returns an error

## How this service works

Roman numeral analysis of a chord progression in a key: numerals, inversions, borrowed chords, secondary dominants.

## Output

Returns a list of Roman numeral labels for each chord in the progression, including inversion notation, diatonic status, degree from tonic, borrowed chord flags, and secondary dominant roles, plus a summary and any unrecognized chords.

## 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": [
      "key",
      "progression"
     ],
     "properties": {
      "key": {
       "type": "string",
       "description": "Key of the progression: C, G, Am, F# minor"
      },
      "progression": {
       "type": "string",
       "description": "Chords separated by spaces, commas or bars: C Am F G7"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "key": {
       "type": [
        "null",
        "string"
       ]
      },
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "analysis": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "object",
        "properties": {
         "role": {
          "type": [
           "null",
           "string"
          ]
         },
         "root": {
          "type": [
           "null",
           "string"
          ]
         },
         "chord": {
          "type": [
           "null",
           "string"
          ]
         },
         "numeral": {
          "type": [
           "null",
           "string"
          ]
         },
         "diatonic": {
          "type": [
           "boolean",
           "null"
          ]
         },
         "diatonicNote": {
          "type": [
           "null",
           "string"
          ]
         },
         "degreeFromTonic": {
          "type": [
           "null",
           "number"
          ]
         }
        }
       }
      },
      "degraded": {
 
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/music-theory-roman-numeral-analysis-2b20166b/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)