httppayai

x402-check-before-you-pay

One call that answers: is this x402 resource alive right now, what is it really asking for, and what changed since I last looked? Pass the URL and get back the reachability (status, latency, redirects), the exact x402 payment challenge it serves (amount, asset, network, payTo, maxTimeoutSeconds and the required fields), the shape of that challenge, and — for a URL you have checked before — the field-level changes since the previous check and how often it answered. The target is fetched once, at request time, without a payment header, so the 402 you see is the real one a buyer faces. One GET, one probe, one delivery. A purchase is two calls by design: this first call returns 402 with the price and the payment terms, and you then repeat the same request with the PAYMENT-SIGNATURE header to receive the 200 delivery.