APIs and AI agents that pay per request.
x402 turns the web's unused "402 Payment Required" status into a payment step. A server asks for a few cents in stablecoin, the client pays, and the request goes through with a receipt. No accounts, no invoices.
Request
The app or agent calls the API like any other.
402 challenge
The server answers with the price, currency, network and a one-time invoice.
Pay
The client pays in stablecoin and gets a transaction hash.
Retry with proof
The client sends the hash back. The server checks it on the ledger and returns the data with a receipt.
Live against this site's API
Watch a real 402 round trip.
This calls /api/x402/demo for real. The payment step is sandboxed: the proof is format-checked, not verified on-chain.
Price in this demo: $0.05 USDC per call.
Revenue gate, settled in USDC
Put x402 in front of what already exists: pilot telemetry, the Basel stress-tester, the ISO 20022 generator, the contract forge and proof-of-reserve feeds. Agents already hold USDC on Base, and UnyKorn issues nothing.
Settled in a client's own token
For a white-label client whose agents, suppliers and services pay each other. On XRPL it's an issued-currency payment with the invoice ID on-ledger. On EVM, the standard scheme needs signed transfer authorizations (EIP-3009).
Where it pays off
Small payments that used to be impossible.
City data services
Permit lookups, parcel records and transit feeds billed per call to commercial users, free to residents.
AI agents
Agents buy data, compute or verification on their own, within a spending limit you set.
Proof on demand
Charge a few cents to verify a document, a receipt or a credential against the ledger.