What is x402?

x402 revives the HTTP 402 Payment Required status code as the basis for pay-per-request access. Its documentation describes it as an open standard, licensed under Apache-2.0, for services that want to charge for APIs and content, with no need for accounts, sessions, or credential management on the buyer's side.

The flow has five steps. A buyer requests a resource. If payment is needed, the server replies with 402 and payment instructions. The buyer prepares and submits a payment payload. The server then verifies and settles the payment itself, or hands that work to a facilitator through its verify and settle endpoints. If the payment is valid, the server returns the resource.

The docs name buyers, which can be human developers or AI agents, sellers who monetize APIs or content, and the optional facilitator. They describe the payments as crypto-native and mention support for micropayments, and the one network the introduction names is EVM, for batched onchain settlement.

Because a buyer can be an AI agent, the docs present x402 as a way for agents to pay for API access on their own. The documentation source lives in the x402-foundation/x402 repository.