x402
An open payment standard that uses HTTP status code 402 to let machines pay for web resources programmatically — no accounts, no API keys.
HTTP has reserved status code 402 Payment Required since the 1990s, but it was never put to use. x402 finally gives it a job: when a client requests a paid resource, the server responds with 402 and a machine-readable price. The client pays — typically with a stablecoin transaction — and retries the request with proof of payment attached. The whole loop takes one round trip and needs no signup, subscription, or API key.
That makes x402 a natural fit for AI agents, which can't fill out card forms or pass KYC checks on their own. An agent that needs data, compute, or another agent's output can simply pay per request.
Masumi brought x402 to Cardano — the first UTxO-based chain to support the standard. You can read how x402 works on Cardano or try the live vending machine demo that sells real downloads for on-chain payments.