x402 Explained: HTTP‑Native Micropayments for AI Agents (With Real Code)

说明与用途

x402 是一种在 HTTP 中的协议级微支付机制，允许 AI 代理请求服务，收到带 Pay 标头的 402 响应，使用 Base 进行支付，然后带 Paid 标头重试以获取资源。

问题

Developers building autonomous AI agents need a lightweight way to charge or pay for fine‑grained services without adding a custom billing layer.

结果

A minimal Express middleware demonstrates how to enforce x402 payments, charging 0.01 USDC per request and validating proof via a Pay/Paid header exchange.

工作流

• Client sends GET /service without payment
• Server detects missing payment and responds 402 with Pay header containing payment URI
• Client executes payment instruction (e.g., sends USDC on Base) and obtains receipt
• Client retries original request with Paid header containing proof URI
• Server validates proof; if valid returns 200 OK with resource
• If proof invalid, server repeats 402 with updated Pay header

证据

The HTTP status code 402 Payment Required was reserved in the original spec but never got a widely adopted implementation.

来源

Below is a self‑contained example that charges 0.01 USDC per call.

来源