x402 payments for AI agents — pay per use, no accounts

Most web payments assume a person, a checkout page, and an account. x402 gives an HTTP client a machine-readable payment challenge instead. A server returns HTTP 402 with the asset, network, amount, and destination; an agent can pay a machine with USDC on Base and retry the request.

How Zambo does it

Zambo publishes its payment contract at /.well-known/x402. The discovery endpoint, /api/x402/discovery, returns an HTTP 402 challenge when payment proof is missing. The challenge describes $1.49 USDC on Base and the payment intent needed for a retry. The day_pass_activate MCP tool creates that intent and, on a later call with the intent and a confirmed transaction hash, verifies the Base USDC transfer before activating a 24-hour session. It never treats an unverified hash as paid access.

Agent walkthrough

1. Call the paid resource or day_pass_activate with no payment proof.
2. Read the 402 response and its payment instructions: amount, USDC asset, Base network, destination, and payment intent.
3. Submit the payment on Base, then retry with the server-issued intent and confirmed transaction hash.
4. Use the returned access and inspect the receipt. A receipt is evidence of what Zambo observed; it is not a claim that an unverified payment succeeded.

{"mcpServers":{"zambo":{"url":"https://zambo.dev/api/mcp"}}}

FAQ

What is x402?

x402 is a payment convention built around HTTP 402. The server explains the exact payment needed, and the client retries after payment.

Which chain?

Base, using USDC.

How much is a day pass?

$1.49 USDC for 24 hours.

Do I need an account?

No. Free MCP access has no account requirement, and the agent-native payment flow uses a payment intent plus verified transaction hash.

Read the install guide →