# WCAG 2.1 Contrast Ratio Checker

> WCAG 2.1 Contrast Ratio Checker is a paid API for AI agents from api.24klabs.ai, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-12).

Computes the WCAG 2.1 contrast ratio between two colors and reports AA/AAA pass/fail status for normal and large text.

## Facts

- Endpoint: POST https://api.24klabs.ai/api/wcag-contrast?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/wcag-2-1-contrast-ratio-checker-4eac02e1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_CTq12m0vRuOEPoeOhuWwV

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 wcag-2-1-contrast-ratio-checker-4eac02e1 -d '<json body>'
```

Example prompt: Can you check whether white text (#FFFFFF) on a navy background (#1A237E) passes WCAG 2.1 AA and AAA standards for both normal and large text?

## When to prefer this

Choose this endpoint when you need a programmatic, standards-accurate WCAG 2.1 contrast ratio computation with explicit AA/AAA pass/fail verdicts for both normal and large text. Prefer it over manual calculations or generic color tools when building automated accessibility audits, CI/CD design checks, or agent workflows that need structured pass/fail output.

## Known failure modes

- Invalid color format provided (non-hex, malformed RGB) returns a 400 error
- Missing foreground or background parameter returns validation error
- Identical foreground and background colors returns a contrast ratio of 1:1 with all fail results
- Unsupported color space or alpha channel values may not be handled correctly

## How this service works

Compute the WCAG 2.1 contrast ratio between a foreground and background color and report AA/AAA pass/fail for normal and large text.

## Output

Returns the numeric WCAG 2.1 contrast ratio (e.g. 4.5:1) between the foreground and background color, along with boolean pass/fail indicators for AA and AAA compliance levels at both normal text (4.5:1 and 7:1 thresholds) and large text (3:1 and 4.5:1 thresholds).

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "bg": {
   "type": "string"
  },
  "fg": {
   "type": "string"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ratio": 4.48,
  "AA_normal": true,
  "AAA_normal": false
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/wcag-2-1-contrast-ratio-checker-4eac02e1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.24klabs.ai](https://www.zero.xyz/host/api.24klabs.ai/llms.txt)