WCAG Contrast Checker API

GET /api/a11y/contrast $0.001 per call USDC on Base · x402

WCAG contrast ratio between two colors — the check the URL-based a11y endpoint can't do. Give a foreground and background color (hex or rgb()); returns the exact ratio and AA/AAA pass/fail for normal text, large text, and UI components, with a plain-English verdict. ?fg=&bg=

Parameters

Name	In		Description
`fg`	query	required	Foreground/text color — hex (#111 or #111111) or rgb()
`bg`	query	required	Background color — hex or rgb()

Example request

curl "https://api.webbersites.com/api/a11y/contrast?fg=%23767676&bg=%23ffffff"
# first call returns 402 + payment requirements; an x402 client pays and retries automatically

Example response

{
    "foreground": "#767676",
    "background": "#ffffff",
    "contrast_ratio": 4.54,
    "ratio_string": "4.54:1",
    "passes": {
        "normal_text": {
            "AA": true,
            "AAA": false
        },
        "large_text": {
            "AA": true,
            "AAA": true
        }
    },
    "summary": "Good — passes AA for normal text and AAA for large text."
}

MCP tool: get_a11y_contrast — via npx -y webbersites-x402-mcp (local, key stays on your machine) or the remote endpoint https://api.webbersites.com/mcp.

How payment works

There is no signup and no API key. Call the endpoint; it replies 402 Payment Required with machine-readable payment requirements. Your client signs a USDC transfer authorization (EIP-3009, gasless) and retries with the X-PAYMENT header — @x402/fetch does this automatically. See the overview for a working snippet.