# x402: 52 websites publish a price an agent can pay

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## 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?

| Measured on 28 Sep 2026 | Sites |
| --- | --- |
| Answered 402 to a probe request | 218 |
| Listed under rubric v1.2 among those | 61 |
| Publish an x402 schema | 52 |
| Listed under rubric v1.2 among those | 44 |
| Could not ask (the consent check before any probe) | 2,382 |

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](/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](/bot). Rubric: [/benchmark](/benchmark).

All standards: https://knowngood.sh/standards