WritersLogic Verifiable AI Agent Hub Chord Check API
The Chord Check API from WritersLogic Verifiable AI Agent Hub — 1 operation(s) for chord check.
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curl "https://apis.io/api/v1/apis/writerslogic-com:writerslogic-com-chord-check-api"
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OpenAPI Specification
openapi: 3.2.0
info:
title: WritersLogic Verifiable AI Agent Hub Chord Check API
version: 2.0.0
description: Pay-per-call agents settled in USDC on Base via x402. Every response carries a signed provenance envelope.
contact:
name: WritersLogic
url: https://writerslogic.com/agents
email: agents@writerslogic.com
servers:
- url: https://agents.writerslogic.com
tags:
- name: Chord Check
paths:
/api/v1/chord-check:
post:
operationId: chord_check
summary: 'Chord check: identify, spell, key membership, transpose'
description: 'Names a chord from its notes, spells a chord symbol into notes, tests whether a chord is diatonic to a key, or transposes a chord symbol, using pitch-class arithmetic over a fixed table of 21 chord qualities, for agents handling lead sheets and music metadata. Rule-based and labelled: when several readings are equally valid (C E G A is C6 or Am7/C) or no quality in the table matches, it returns unknown with the candidates instead of choosing. Does NOT use harmonic context, analyse progressions, infer keys, or know quality names outside its table.
Price: 0.005 USDC on Base (x402).'
x-x402-price-usdc: '0.005'
x-x402-amount: '5000'
x-payment-info:
protocols:
- x402
price:
mode: fixed
currency: USD
amount: '0.005'
x-audience: business
x-sample-url: https://agents.writerslogic.com/api/v1/samples/chord-check
security:
- x402: []
- apiKey: []
requestBody:
required: true
content:
application/json:
schema:
type: object
additionalProperties: false
required:
- operation
properties:
operation:
type: string
enum:
- identify
- spell
- key-membership
- transpose
notes:
type: array
items:
type: string
maxLength: 6
description: Note name such as C, Eb, F#, Bbb, C##, optionally with octave (C4). Bass is the lowest note when every note has an octave, else the first.
maxItems: 8
minItems: 2
description: 'For identify: 2 to 8 notes.'
chord:
type: string
maxLength: 24
description: 'Chord symbol, root A-G with optional #/b, quality suffix, optional /bass: Cmaj7, F#m7b5, Bb/D.'
key:
type: object
additionalProperties: false
required:
- tonic
description: For key-membership.
properties:
tonic:
type: string
maxLength: 3
description: Key tonic, e.g. A or Eb.
mode:
type: string
enum:
- major
- minor
- harmonic-minor
description: Default major. minor is natural minor.
semitones:
type: integer
description: 'For transpose: semitones up (negative down).'
minimum: -48
maximum: 48
prefer:
type: string
enum:
- sharps
- flats
description: 'Accidentals for a natural root when transposing. Default sharps; a root written with # or b keeps its kind.'
expectChord:
type: string
maxLength: 24
description: Optional claimed chord symbol to verify (identify, transpose).
expectNotes:
type: array
items:
type: string
maxLength: 4
description: A claimed note name.
maxItems: 8
description: Optional claimed notes in order, to verify (spell).
example:
operation: spell
chord: Ebmaj7
expectNotes:
- Eb
- G
- Bb
- D
responses:
'200':
description: Paid result with provenance
content:
application/json:
schema:
type: object
properties:
data:
type: object
properties:
status:
type: string
enum:
- pass
- fail
- unknown
- unsupported
description: 'pass: every rule held. fail: a rule was violated (see witnesses). unknown: the input lacks the evidence to decide. unsupported: outside what this engine covers. Missing evidence is never a pass.'
operation:
type: string
chord:
type: string
maxLength: 200
description: Normalised chord symbol.
readings:
type: array
items:
type: object
properties:
root:
type: string
quality:
type: string
symbol:
type: string
bass:
type: string
rootPosition:
type: boolean
rootPc:
type: integer
bassPc:
type: integer
notes:
type: array
items:
type: string
description: Spelled chord tones, bass first when it is not a chord tone.
pitchClasses:
type: array
items:
type: integer
description: Sorted pitch classes, C = 0.
diatonic:
type: boolean
outOfKey:
type: array
items:
type: string
degree:
type: integer
description: Scale degree of the chord root when it is in the scale.
scale:
type: array
items:
type: string
witnesses:
type: array
items:
type: object
properties:
ruleId:
type: string
detail:
type: string
path:
type: string
description: JSON pointer or dotted path into the input.
offset:
type: integer
index:
type: integer
expected:
description: What the rule required.
actual:
description: What the input had.
versions:
type: object
description: Every semantic dependency of this answer (engine, tables and their as-of dates, tokenizer, calendar, rounding profile).
limits:
type: array
items:
type: string
deterministic:
type: boolean
description: 'Always true: pure code, no model.'
_provenance:
type: object
description: C2PA-aligned manifest and W3C VC 2.0 (eddsa-jcs-2022) issued by the hub DID; verify at POST /api/v1/verify-provenance
required:
- data
- _provenance
'400':
description: Invalid request (no payment consumed)
content:
application/json:
schema:
type: object
properties:
error:
type: string
code:
type: string
'401':
description: Invalid X-API-KEY
content:
application/json:
schema:
type: object
properties:
error:
type: string
code:
type: string
'402':
description: Payment required or invalid
content:
application/json:
schema:
type: object
description: x402 v2 PaymentRequired (also base64 in the PAYMENT-REQUIRED header)
properties:
x402Version:
type: integer
error:
type: string
code:
type: string
resource:
type: object
accepts:
type: array
items:
type: object
extensions:
type: object
'502':
description: Upstream failure; the payment is released or not settled
content:
application/json:
schema:
type: object
properties:
error:
type: string
code:
type: string
tags:
- Chord Check
components:
securitySchemes:
x402:
type: apiKey
in: header
name: PAYMENT-SIGNATURE
description: x402 v2 payment payload (base64) sent after a 402 challenge
apiKey:
type: apiKey
in: header
name: X-API-KEY