x402 Protocol & x402-rs Development Guide

The x402 protocol activates the long-dormant HTTP 402 Payment Required status code to enable blockchain payments directly through HTTP. The client never touches the blockchain directly — it produces a cryptographic signature, and a facilitator verifies and settles the payment on-chain.

Three Actors

  Client                    Resource Server              Facilitator
    |                             |                          |
    | 1. GET /paid-content        |                          |
    |---------------------------->|                          |
    | 2. 402 Payment Required     |                          |
    |    Payment-Required: <b64>  |                          |
    |<----------------------------|                          |
    | 3. Sign payment (off-chain) |                          |
    | 4. GET /paid-content        |                          |
    |    Payment-Signature: <b64> |                          |
    |---------------------------->|                          |
    |                             | 5. POST /verify          |