How x402 works end-to-end: HTTP 402 → signed USDC → settled data
x402 turns HTTP's long-reserved 402 Payment Required status into
a working machine-payment rail. Here is the full lifecycle of one paid request
against a live implementation (this API), with real numbers.
1. The challenge
An agent GETs https://api.newsgurus.ai/x402/regime with no payment. The server
responds 402 with payment requirements: the scheme
(exact), network (eip155:8453 — Base mainnet), the
asset (USDC, 0x8335…2913), the receiving address, and
maxAmountRequired (e.g. 2000 = $0.002 in 6-decimal
USDC units).
2. The signature (gasless for the payer)
The agent signs an EIP-3009 transferWithAuthorization
message: "transfer exactly this many USDC units from my wallet to that address,
valid for this time window, with this nonce." Signing costs nothing and needs
no ETH — the payer never submits an on-chain transaction.
3. The retry
The agent repeats the request with the signed payload attached (x402 v2
header transport: PAYMENT-SIGNATURE; v1 clients use
X-PAYMENT). The server forwards it to a
facilitator (Coinbase CDP's — free to sellers) which verifies
the signature, amount, and nonce.
4. Verify → respond → settle (in that order)
Only after verification passes does the route handler run and return data. The facilitator then submits the authorization on-chain and the USDC lands in the seller's wallet — every sale is publicly auditable. The invariant worth copying if you build your own: verify before work, settle after success, and never withhold a response because settlement lagged.
What this enables
- No accounts: the wallet is the identity; payment is the auth.
- True micropricing: $0.002 calls are viable — no card minimums, no invoicing.
- Agent-native discovery: sellers publish machine catalogs (/.well-known/x402.json, llms.txt) and indexers like the CDP Bazaar and x402scan catalog them from settled payments — agents find and pay suppliers with no human introduction.
See it live
# the menu (free)
curl https://api.newsgurus.ai/x402/catalog
# the raw 402 challenge (free to look at)
curl -i https://api.newsgurus.ai/x402/regimeTo complete a purchase from code, start at the buyer guide — about ten lines of Python.