Paying with x402

x402 revives HTTP 402 Payment Required for machine payments. Premium endpoints quote a price, your agent signs a USDC transfer authorization, and the content is released once a facilitator settles it on Base Sepolia (testnet). Accounts and API keys are not needed.

API & quickstart Payments (x402)MCP server Pricing

Terms

Price	$0.20 USD per premium request (200000 atomic units of USDC)
Network	Base Sepolia (testnet) (`eip155:84532`)
Asset	USDC `0x036CbD53842c5426634e7929541eC2318f3dCF7e`
Scheme	`exact` (EIP-3009 transferWithAuthorization; gasless for the payer)
Pay to	being configured
Protocol versions	x402 v2 (`PAYMENT-REQUIRED` / `PAYMENT-SIGNATURE` / `PAYMENT-RESPONSE`) and legacy v1 (`X-PAYMENT` / `X-PAYMENT-RESPONSE`)

Flow

Request a premium URL. You get 402 with a base64 JSON PAYMENT-REQUIRED header (v2). The JSON body repeats the terms in v1 format and includes a free preview.
Your client picks accepts[0], signs an EIP-3009 authorization for the exact amount to payTo, and retries with PAYMENT-SIGNATURE (v2) or X-PAYMENT (v1).
We verify the payment with the facilitator, build your response, settle on-chain, and only then return 200 with a PAYMENT-RESPONSE header containing the transaction hash.
Keep the X-Archive-Receipt header: sending it back as X-Archive-Receipt (or Authorization: Receipt …) re-serves the same resource free for 24 hours.

Guarantees

Nothing is charged for missing resources (404 before any payment request), handler errors, or failed settlements.
Paid responses are marked Cache-Control: private, no-store.
The price in the 402 quote is the price you pay. Payment authorizations expire after 5 minutes.

MCP payments

Paid MCP tools follow the x402 MCP transport: an unpaid tools/call returns an error result whose structuredContent is the PaymentRequired object; retry the call with the payment in params._meta["x402/payment"]. The settlement receipt comes back in result._meta["x402/payment-response"]. See MCP.

Humans

Dossier pages include a wallet button that does the same thing in your browser with any EIP-1193 wallet (for example MetaMask or Coinbase Wallet).