x402

x402 is a protocol for paying for an HTTP resource in the request itself. A server that wants payment responds with status 402 and a payment-requirements header describing what it accepts — asset, amount, chain, the address to pay. The client constructs a signed payment payload, attaches it to a retried request, and the server (usually through a facilitator) verifies and settles it before serving the response. The whole loop is machine-readable, so a program can complete it without an account, an API key or a checkout page.

In practice most settlement uses a stablecoin transfer authorised by signature (EIP-3009 transferWithAuthorization on EVM chains), which lets the server or facilitator submit the transfer and pay gas. x402 is published by Coinbase and is open; several facilitators and client libraries implement it.

x402 is not a marketplace, a token or a guarantee that a resource is worth paying for. A server that speaks x402 has declared a price; nothing in the protocol says the response is correct. And a listing tagged x402 has told Sato Hub it implements the standard — whether it settles real payments is a separate question, measured on the venue page.