x402 Protocol Enables AI Agents to Make Autonomous Micropayments via HTTP
The x402 specification repurposes HTTP's long-dormant 402 status code to create a payment negotiation channel between AI agents and paid API services. When a server requires payment, it returns a 402 response with details such as amount, token, blockchain, and a nonce to prevent replay attacks. The client then signs and submits an on-chain ERC-20 transaction, attaching the transaction hash in a retry request header. Because the entire flow operates within standard HTTP headers and response bodies, no new protocol layer is required. Developers can implement x402 using existing tools like the viem library for Ethereum wallet interactions and standard HTTP clients.
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