x402: 52 websites publish a price an agent can pay
What is x402?
x402 is an open payments protocol built on HTTP: when a resource requires payment, the server answers with status 402 and a PAYMENT-REQUIRED header carrying a base64-encoded PaymentRequired object that states the price and how to pay; the client retries with a PAYMENT-SIGNATURE header carrying its authorisation, and the server confirms settlement in a PAYMENT-RESPONSE header. It was designed for machine-to-machine payments, which is why it matters to an index of sites agents can act on: it is how a site charges an agent without an account, a card form, or a person. The specification is published in the open at x402.org, currently at v2 of its HTTP transport.
How does Known Good check it?
Two things, separately. First, whether any request the probe made returned a 402: that is a site asking to be paid. 67 of those answers carried a PAYMENT-REQUIRED header, the protocol's own terms. Second, whether the site publishes an x402 schema the probe can read without paying. The probe never pays and never retries with a signature; it records the ask and the schema, and stops.
How many websites use x402?
A 402 alone is a door that asks for money; the schema is the price list beside it. 44 of the sites with a schema are listed because something else on the site answered, since a payment ask is not by itself a check in the rubric.
Does x402 make a site agent-ready?
It makes a site payable, which is a different thing. Rubric v1.2 lists a site on signals that answer without payment. Whether a paid request counts as a capability is an open question for a later rubric version.
How do I add x402 to my site?
Answer 402 with a PAYMENT-REQUIRED header on the resources you charge for, following the x402 HTTP transport specification, and publish the schema so a client can read the price before it tries. Then ask for a probe at /submit.
Frequently asked
Does Known Good pay to test a site? No. The probe records the 402 and the schema and never sends a payment.
Is a 402 a failure? No. It is recorded as a payment ask, separately from pass, fail and could-not-ask.
Counts are of sites (hostnames), measured by Known Good's probe on 28 Sep 2026. Could-not-ask is counted beside the total, never inside it. Method: /bot. Rubric: /benchmark.