I'm going to show you the actual plumbing of a live x402 service — including the two bugs that only showed up with real payments, and the pricing mistake we fixed on day one.
Quick disclosure: this service was designed, coded, and deployed by Conway, an autonomous Claude-based agent I supervise. I'm a non-developer; the agent wrote every line, and I approve anything irreversible. That's part of the experiment.
Every transaction starts with a question nobody budgets for: who am I paying? Sending to a Base address usually means pasting hex and hoping. The chain knows whether that address is a contract or a wallet, whether it's ever been used, what it holds — but packaging that answer per-request, payable by a machine without an API-key signup, wasn't a thing until x402.
So: Conway Address Intel — GET /report/{address}
returns a structured due-diligence report for $0.02 USDC, paid inline via HTTP 402. A free /overview/{address}
returns the preview (contract vs wallet, holds-funds, activity bucket) with no wallet needed at all.
With x402-express
, the middleware answers 402 with signed terms, verifies the buyer's USDC authorization through a facilitator, and settles after your handler responds:
import { paymentMiddleware } from "x402-express";
import { facilitator } from "@coinbase/x402"; // mainnet, auth via CDP keys
app.use(paymentMiddleware(
PAY_TO_WALLET,
{ "GET /report/*": { price: "$0.02", network: "base" } },
facilitator,
));
The buyer side is just as short with x402-fetch
:
import { wrapFetchWithPayment } from "x402-fetch";
import { privateKeyToAccount } from "viem/accounts";
const payFetch = wrapFetchWithPayment(fetch, privateKeyToAccount(KEY));
const res = await payFetch("https://.../report/0x4200...0006");
// 402 → sign EIP-3009 USDC auth → retry → 200. Buyer needs zero ETH; facilitator pays gas.
1. Settlement happens after your handler responds. We logged receipts inside the handler and every real payment got recorded as "SIMULATED" — the settlement header didn't exist yet. Fix: read
X-PAYMENT-RESPONSE
in res.on("finish")
. Our first real testnet settlement is forever mislabeled in the ledger, with an append-only correction entry after it. Ledgers don't get edited.2. Validate before the payment layer, or buyers can pay for garbage. Middleware order matters: our address validation runs before paymentMiddleware
, so GET /report/0xNOTANADDRESS
gets a 400 that says "you have not been charged" — and that's structurally true, terms are never even offered.
3. Test the failure path with real money. We pointed the service at a dead RPC and made a real (testnet) payment attempt: handler 503'd, and the middleware — which only settles 2xx responses — never charged the buyer. "Failed requests are never charged" is now a claim we've watched happen, not a hope.
We launched at $0.50/report. Then we read the room: x402 services cluster around $0.02–0.03/call. At 20× the median, nobody impulse-tests you — and impulse tests are the entire top of funnel when your buyers are other people's agents. We repriced to $0.02 and made the preview free. Marginal cost is ~zero (pure RPC reads), so every call at any price is margin; the bet is volume and integration, not markup.
Here's the funny part: the main x402 discovery index (the Bazaar) lists you automatically on your first settlement — there's no submission form. So a brand-new service needs its first paying customer to become findable by paying customers. Our solution: a free endpoint anyone can integrate without funds, a machine-readable manifest at /.well-known/x402
, an honest /status
page (counters reset each deploy — it says so), and showing up in the places x402 builders actually talk.
curl https://conway-address-intel-production.up.railway.app/overview/0x4200000000000000000000000000000000000006
Full report is 2¢ via any x402 client. Manifest: /.well-known/x402 · Status:
/status
/faq
Honest scope, stated plainly: live public onchain data only. Not a security audit, not scam detection, not financial advice. If your x402 client chokes on our 402 flow, tell me — the agent fixes fast.
As of publishing, this service has settled exactly zero mainnet dollars — our first buyer's 2¢ literally puts us on the map (the Bazaar indexes on first settlement). Want the permanent line in an AI agent's append-only ledger? It's available.