The Contrast Fix API from WritersLogic Verifiable AI Agent Hub — 1 operation(s) for contrast fix.
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openapi: 3.2.0
info:
title: WritersLogic Verifiable AI Agent Hub Contrast Fix 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: Contrast Fix
paths:
/api/v1/contrast-fix:
post:
operationId: contrast_fix
summary: WCAG 2.2 contrast check with the minimal OKLCH lightness fix and colour-blind…
description: 'Checks up to 50 foreground/background hex pairs against a WCAG 2.2 contrast threshold (4.5 AA text, 3 large text and UI, 7 AAA, or your own) on the unrounded ratio, so 4.499 fails and exactly 4.5 passes, and for a failing pair returns the closest colour by OKLCH lightness (chroma and hue held, gamut-clipped, 8-bit) that meets it. Optionally simulates protanomaly, deuteranomaly and tritanomaly (Machado et al. 2009, any severity, 1.0 is dichromacy) and reports whether the pair stays distinguishable by OKLab distance against your threshold. Built for designers and agents generating palettes. It does not evaluate APCA, text size or weight, opacity, images, gradients or colour spaces other than sRGB, and the colour-blind result is a simulation, not a medical assessment.
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/contrast-fix
security:
- x402: []
- apiKey: []
requestBody:
required: true
content:
application/json:
schema:
type: object
additionalProperties: false
required:
- pairs
properties:
pairs:
type: array
items:
type: object
required:
- foreground
- background
properties:
foreground:
type: string
maxLength: 7
description: '#rgb or #rrggbb (strict hex; no names, no alpha).'
pattern: ^#([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$
background:
type: string
maxLength: 7
description: '#rgb or #rrggbb.'
pattern: ^#([0-9a-fA-F]{3}|[0-9a-fA-F]{6})$
label:
type: string
maxLength: 80
description: Caller label echoed back.
claimedRatio:
type: number
description: A ratio the caller asserts; compared to the unrounded ratio with a 0.01 tolerance.
minimum: 1
maximum: 21
maxItems: 50
minItems: 1
description: Foreground/background pairs.
level:
type: string
enum:
- aa-normal
- aa-large
- aaa-normal
- aaa-large
- non-text
description: aa-normal 4.5 (default), aa-large 3, aaa-normal 7, aaa-large 4.5, non-text 3 (WCAG 2.2 SC 1.4.3, 1.4.6, 1.4.11).
threshold:
type: number
description: 'Overrides level: the minimum contrast ratio.'
minimum: 1
maximum: 21
fixTarget:
type: string
enum:
- foreground
- background
- none
description: Which colour to move for a failing pair (default foreground); none skips the fix.
cvdSeverity:
type: number
description: Enables the colour-vision-deficiency check at this severity, 0 to 1 (1.0 is dichromacy); between the published 0.1 steps the matrices are interpolated.
minimum: 0
maximum: 1
cvdMinDeltaE:
type: number
description: Smallest OKLab distance counted as distinguishable (default 0.05, a heuristic, not a standard).
minimum: 0
maximum: 2
example:
pairs:
- foreground: '#767676'
background: '#ffffff'
- foreground: '#777777'
background: '#ffffff'
label: caption
level: aa-normal
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.'
threshold:
type: number
description: The contrast ratio applied.
results:
type: array
items:
type: object
properties:
label:
type: string
foreground:
type: string
background:
type: string
ratio:
type: number
description: Unrounded WCAG contrast ratio.
ratioText:
type: string
description: Truncated (never rounded up) to two decimals.
meets:
type: boolean
fix:
type: object
description: 'status found: hex, ratio, direction, deltaL (change in OKLab L), gamutClipped, oklch of the result. status unreachable: no lightness at this chroma and hue reaches the threshold.'
cvd:
type: array
items:
type: object
description: 'Per deficiency: simulated hex pair, OKLab deltaE, contrast of the simulated pair, distinguishable.'
maxItems: 3
maxItems: 50
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:
- Contrast Fix
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