x402 payments

What it checks

x402 revives the long-unused HTTP 402 Payment Required status. A paid endpoint answers an unpaid request with 402 and the payment terms; the agent pays and retries with proof of payment.

The extension requests /.well-known/x402 and /.well-known/x402.json, in that order, and passes on the first one that returns a non-empty JSON document. If neither is there, it checks whether the homepage response carries an X-402 or WWW-Authenticate header. Any WWW-Authenticate header counts, so a page behind HTTP authentication also passes.

Commerce protocols are new, and most sites have no reason to support them, so absence is N/A rather than a failure.

Results

Status	When
Pass	One of the paths returns a non-empty JSON document, or the homepage sends one of the headers
N/A	Nothing was found

How to fix

Implement the x402 flow on the endpoints you charge for, and publish a descriptor at /.well-known/x402 so agents can find out before they hit a 402. Serve it as JSON (Content-Type: application/json); the extension only confirms a JSON document is there and does not validate its contents.

These standards are still settling, so follow the protocol’s own documentation for what the descriptor should contain.