x402 is an open protocol for internet-native payments. A resource server can describe the price of an API, file or computation in an HTTP 402 Payment Required response. A client authorizes the payment and retries the same request with a signed payload.
It is not a new payment network. It is a shared language between the client, the resource server and payment infrastructure.
The basic exchange
GET /v1/data HTTP/1.1
Host: api.example.com
HTTP/1.1 402 Payment Required
PAYMENT-REQUIRED: eyJ4NDAyVmVyc2lvbiI6Miwi...In the current V2 wire format, the client returns a PAYMENT-SIGNATURE header. The server verifies the payload locally or through a facilitator, performs the paid operation, settles the payment and returns the resource.
The participants
Client
A program, application or AI agent that wants a paid resource and can authorize one of the payment options offered by the server.
Resource server
The HTTP service that prices and protects a resource. It remains responsible for authorization rules, product behavior and safe failure handling.
Facilitator
An optional service that verifies and settles payments for supported scheme and network combinations. A resource server can also perform these functions itself.
Why agents care
Traditional API access often requires account creation, prepaid credits, subscriptions and long-lived API keys. x402 can make price discovery and payment part of the same programmatic exchange as the resource request.
| Traditional access | x402-style access |
|---|---|
| Create an account | Request the resource |
| Add billing details | Receive machine-readable terms |
| Buy credits | Authorize the exact interaction |
| Manage an API key | Retry with the payment payload |
This does not remove risk. Agents still need spending limits, domain trust policies, idempotency and an audit trail.
What it does not solve
x402 does not choose a price, guarantee the quality of a resource, make delivery and settlement automatically atomic, or replace tax and compliance work. Those remain product and operational responsibilities.
Treat a 402 response as an offer, not as proof that a service is trustworthy.
Source of truth
The x402 Foundation repository contains the open specification, SDKs and current payment-scheme documents. Check the exact protocol and package versions before building a production integration.