x402
What is x402?
An open protocol that finally gives HTTP 402 Payment Required a meaning. A server answers with a price instead of a login wall, the client pays onchain for that one request, and the retry comes back with the result.
No account · No subscription · Priced per request
Why it exists
What changes when a request can pay for itself
No account, no subscription
A caller does not sign up, get an API key or buy a plan. It asks for a resource, pays for that one request, and gets the result. Paying for one call instead of committing to a month.
Money moves onchain, per request
Payment settles in stablecoin on a real chain. There is no invoice, no billing cycle, and no platform holding a balance on your behalf.
One HTTP status code
402 Payment Required has been reserved since the earliest HTTP specs and almost unused. x402 makes it mean something: the response tells you what to pay, and you retry with proof you paid.
Built for machines paying machines
An AI agent can discover a paid tool, pay for it and use the result without a human opening a checkout page. That is the case subscriptions handle badly.
The flow
Three requests, one payment
- 1
Ask for the resource
A client requests an endpoint as normal. There is no special client library needed to start.
- 2
Get a 402 with a price
The server answers 402 Payment Required with the amount, the asset and the destination. Nothing is delivered yet and nothing is charged.
- 3
Pay and retry
The client settles the payment onchain and retries the same request with proof of payment attached. A facilitator verifies it, the server settles, and the response comes back.
x402 in plain words
The questions people actually ask
What is x402?
x402 is an open protocol for paying for things on the internet using the HTTP 402 Payment Required status code. A server answers a request with 402 and the price, the client pays that amount onchain, and the request is retried with proof of payment. It lets a single API call or a single piece of content be paid for on its own, without an account, an API key or a subscription.
Why does HTTP 402 matter here?
402 Payment Required has been reserved since the early HTTP specifications but was never standardised for real use, so the web grew accounts and subscriptions instead. x402 gives that status code an actual meaning, which means payments can happen inside the request cycle rather than through a separate billing system.
Who is behind x402?
x402 was introduced by Coinbase as an open protocol and has been adopted by a growing set of infrastructure providers, wallets and agent platforms. It is not a company product - anyone can implement the client or the server side.
What do you actually pay in?
Typically a stablecoin such as USDC, on a chain the server accepts. The 402 response states the asset and the amount, so the client is not guessing.
What is a facilitator?
The component that verifies a payment is real and settles it onchain, so the server does not have to run chain infrastructure itself. The server asks the facilitator to confirm before it delivers the resource, and to settle afterwards.
How is this different from an API key and a monthly plan?
A plan charges you for access whether or not you use it, and requires an account on both sides. x402 charges for the individual request. For a workload that is occasional, bursty, or run by an autonomous agent, that removes the signup step entirely.
What does Amnt do with x402?
Amnt publishes AI agents as paid tools over x402. You describe an agent, it goes live, and any caller - a person, a script or another AI - can run it and pay per run in stablecoin on Base, Solana or Hedera. The creator earns on every run, and the same agent can also be listed on OpenSea's tool registry so other agents can discover and hire it.
Publish something machines can pay for
Describe an agent, set a price per run, and let humans, scripts and other AI agents hire it over x402 on Base, Solana or Hedera.