Agents are becoming real customers: they browse programmatically, decide fast, and pay per call. But they fail at exactly the steps your current signup flow is made of — account creation, email verification, card entry, key rotation. If buying your API requires a human, an agent can't buy it at all.
The fix is an old HTTP status code: 402 Payment Required.
The x402 pattern in one minute
- A buyer calls your endpoint with no payment.
- You reply
402with a machine-readable challenge: price, currency, recipient address, network. - The buyer pays and retries with a payment proof header.
- You verify (or delegate verification), serve the response, and attach a receipt.
No accounts. No cards. The buyer's wallet is its identity. The protocol is x402, and it settles natively on chains fast and cheap enough for per-call pricing — BSV in this stack.
Option A: hosted, in ten minutes
x402 Gateway wraps your existing API:
- Register the upstream URL and an auth header to inject (your existing API key stays server-side).
- Set a sat price per route and your BSV
payToaddress. - You get a paid endpoint at
/g/<slug>/<tool>and a listing in x402market so agents can find it.
Free tier covers up to 5 routes; Pro ($9/mo) adds 100 routes, per-call analytics, and CSV export. You change nothing about your API.
Option B: self-hosted, in an afternoon
If you want the endpoint to be yours, the pattern is a small Worker (or any server) that:
- returns
402 + PAYMENT-REQUIREDon unpaid calls, - verifies
PAYMENT-SIGNATURE(envelope shape, amount, recipient), - broadcasts the transaction via a facilitator or ARC,
- dedupes txids so a replay can't buy two calls,
- proxies upstream with your credentials.
Reusable pieces exist — the Seller Kit from this factory is exactly this template, and Agent-ready API in 48 hours is the done-for-you version with the listing included.
Pricing that agents can reason about
Agents compare options numerically. Help them:
- Price per call in sats. Sub-cent granularity is a feature, not a rounding error.
- Describe tools precisely. Name, one-line description, parameters. Agents pick tools by description.
- Offer a free probe. A zero-price health or sample route lets agents validate quality before spending.
- Be stable. Fresh 402 challenges on every quote; no expired cached prices.
Discovery: be findable without a website
An agent doesn't land on your pricing page. It queries a registry. In this stack that's x402market: you publish a manifest, the registry verifies it against a live 402 challenge, and buyers quote it without a wallet.
That means your marketing surface is a JSON file and your 402 response — both should be accurate on the first try.
Getting paid
Sats land at your payTo address per call. There is no invoice, settlement delay, or chargeback. If you use the hosted gateway, your address is paid directly; the gateway never custodies funds. If you self-host with a facilitator, the facilitator broadcasts but doesn't hold balances.
For teams that also want fiat, the pattern in this factory is: card top-ups on one side (Stripe), machine-speed settlement on the other (BSV). Humans fund; agents spend.
Checklist
- [ ] Endpoint returns a valid
402 + PAYMENT-REQUIREDwhen unpaid. - [ ] At least one paid route and one free probe.
- [ ] Tool descriptions written for tool-selection, not for landing-page SEO.
- [ ]
payTois an address you control and monitor. - [ ] Txid dedupe in place (one payment, one call).
- [ ] Listing submitted and verified in a registry agents actually query.
- [ ] Usage visible somewhere: calls, sats, errors.
FAQ
Do I need to know Bitcoin to do this?
No. You need an address to receive sats and a way to broadcast transactions. The hosted gateway handles verification and broadcasting for you.
What about bots that hammer the free probe?
Free routes should be genuinely cheap to serve and rate-limited per IP. Paid routes are naturally rate-limited by economics.
Can I keep my existing auth?
Yes — credentials are injected server-side after payment verification. Buyers never see them.
Is x402 only for crypto-native buyers?
The buyers here are agents with wallets (agentpay or otherwise). A human-facing card option can coexist through a separate plan; the point is that the agent path exists at all.
