Date Arithmetic API

Exact date arithmetic — the calendar math LLMs guess at. ?from=&to= → days, business days, weeks, hours between; ?date=&add=30d|2w|3m|1y|10bd → the resulting date (bd = business days); ?date= alone → weekday, ISO week, day-of-year, leap year, unix. All UTC, Mon-Fri business days, real-calendar validation (Feb 30 is rejected).

Parameters

Example request

curl "https://api.webbersites.com/api/calc/dates?from=2026-07-09&to=2026-12-25"
# first call returns 402 + payment requirements; an x402 client pays and retries automatically

Example response

{
    "from": {
        "date": "2026-07-09",
        "weekday": "Thursday"
    },
    "to": {
        "date": "2026-12-25",
        "weekday": "Friday"
    },
    "diff": {
        "days": 169,
        "business_days": 121,
        "weeks": 24.14
    }
}

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.