{"glossary_note":"One entry per term. Each entry answers its own address as JSON.","glossary_rules":{"Sources":"Each entry is pinned to primary sources — a specification, an RFC, an EIP, or a party's own published documents — listed on the entry.","Numbers":"Entry text carries links rather than figures. Where a quantity matters, the entry links the source that holds it, so nothing here can go stale in silence.","Named parties":"A party is described as what it is and does, per its own documents. No ranking, no endorsement, and no comparison between parties."},"glossary":[{"slug":"facilitator","title":"facilitator","kind":"term","short":"A facilitator is a service that verifies and settles x402 payments on behalf of a seller. The seller's endpoint quotes a price, the buyer's client signs a payment authorization, and the facilitator checks that authorization against the quote and submits it to the blockchain.","path":"/glossary/facilitator"},{"slug":"payto","title":"payTo","kind":"term","short":"payTo is the field in an x402 payment quote that names the address a payment is sent to. It travels inside the HTTP 402 challenge, so it is chosen by whoever controls the endpoint at the moment of the quote, and it can differ between one request and the next.","path":"/glossary/payto"},{"slug":"catalogue","title":"catalogue","kind":"term","short":"A catalogue is a published list of x402 endpoints that a buyer or an agent can read to discover what is payable. Facilitators operate them, listing the endpoints that settle through the facilitator, so a listing is a curation decision rather than a property of the endpoint itself.","path":"/glossary/catalogue"},{"slug":"verify-and-settle","title":"verify and settle","kind":"term","short":"Verify and settle are the two operations an x402 facilitator exposes. Verify checks a signed payment payload against the quote the endpoint issued; settle submits that payload to the blockchain. They are separate calls, and a payload that passes verification has still moved no money.","path":"/glossary/verify-and-settle"},{"slug":"accepts-array","title":"accepts array","kind":"term","short":"The accepts array is the body of an x402 payment challenge: the list an endpoint returns with HTTP 402 when a request arrives unpaid. Each element of that array is one payment option the endpoint will take, stated in machine-readable terms.","path":"/glossary/accepts-array"},{"slug":"http-402","title":"HTTP 402","kind":"rail","short":"HTTP 402 is the response status code named Payment Required. RFC 9110 reserves it and defines no payment format, which leaves the meaning of such a response to whatever protocol is layered above it. x402 is one such protocol, and the status code is not the same thing as the protocol.","path":"/glossary/http-402"},{"slug":"settlement","title":"settlement","kind":"term","short":"Settlement is the step where an authorised x402 payment is submitted to the blockchain and the transfer actually happens. A quote, a signature and a successful verification all precede it, and none of them is a settlement.","path":"/glossary/settlement"},{"slug":"x402","title":"x402","kind":"rail","short":"x402 is an open protocol for paying for an HTTP request with a stablecoin transfer, using the HTTP 402 status code to carry the terms. It lets a client — often software rather than a person — pay per call, with no account, no key exchange and no subscription.","path":"/glossary/x402"},{"slug":"eip-3009","title":"EIP-3009","kind":"term","short":"EIP-3009 is an Ethereum token standard extension that lets a token holder sign a transfer authorization off-chain, which anyone can then submit on-chain. It is the mechanism under x402's exact scheme: the payer signs, and the facilitator pays the gas to submit.","path":"/glossary/eip-3009"},{"slug":"mpp","title":"MPP","kind":"rail","short":"MPP — the Machine Payments Protocol — is an open protocol for machine-to-machine payments over HTTP, published at mpp.dev. It uses the HTTP 402 status to carry payment terms, and it is a separate specification with its own schemes and its own supported networks.","path":"/glossary/mpp"},{"slug":"coinbase-cdp","title":"Coinbase Developer Platform (CDP)","kind":"player","short":"Coinbase Developer Platform (CDP) is Coinbase's developer product suite. In the x402 ecosystem it operates a facilitator — the service that verifies and settles payments for sellers that configure it — and publishes the discovery catalogue attached to that facilitator, the x402 Bazaar.","path":"/glossary/coinbase-cdp"},{"slug":"x402-foundation","title":"x402 Foundation","kind":"player","short":"The x402 Foundation is the organization that stewards the x402 specification. The protocol's public repository is published under its GitHub organization, which is the source of record for the schemes, the challenge format and the facilitator operations.","path":"/glossary/x402-foundation"},{"slug":"x402-org-facilitator","title":"x402.org facilitator","kind":"player","short":"The x402.org facilitator is the public facilitator served from the protocol's own project site. It verifies and settles payments for sellers that configure it, and it maintains a discovery catalogue of its own, separate from any other facilitator's.","path":"/glossary/x402-org-facilitator"}],"selected":{"slug":"catalogue","kind":"term","title":"catalogue","question":"What is a catalogue in x402?","short":"A catalogue is a published list of x402 endpoints that a buyer or an agent can read to discover what is payable. Facilitators operate them, listing the endpoints that settle through the facilitator, so a listing is a curation decision rather than a property of the endpoint itself.","mechanism":["Being listed means an endpoint met a catalogue's criteria on the day the catalogue was read. The criteria belong to whoever runs it and are published by them: what qualifies an endpoint, what is shown about it, and the period of inactivity after which a listing is removed. A [facilitator](/glossary/facilitator) that runs a catalogue lists what settles through itself, so an endpoint's listing follows its facilitator.","The catalogues in use on this rail are the ones their facilitators publish. The x402 Bazaar is the catalogue [Coinbase Developer Platform](/glossary/coinbase-cdp) publishes, listing endpoints that settle through its facilitator. A separate catalogue is maintained by the [x402.org facilitator](/glossary/x402-org-facilitator) for the endpoints that settle through that one. An endpoint appears in the catalogue belonging to the facilitator it settles through, so the two lists are not versions of one list.","De-listing leaves no trace. A catalogue publishes its current state, so an endpoint that was removed reads the same as an endpoint that was never there, and the date a listing changed cannot be recovered from the list afterwards. Holding that history at all requires reading the catalogue on a clock and keeping every reading."],"citations":[{"url":"https://docs.cdp.coinbase.com/x402/bazaar","publisher":"Coinbase Developer Platform documentation","title":"x402 Bazaar","read_on":"2026-08-27"},{"url":"https://docs.cdp.coinbase.com/x402/seller/get-discovered","publisher":"Coinbase Developer Platform documentation","title":"Seller: get discovered","read_on":"2026-08-27"}],"handoff":{"routes":["/method"],"sentence":"probe402 reads the catalogues it derives targets from on a fixed clock and retains every capture; how that capture works is set out in [the method](/method)."},"related":[{"slug":"facilitator","title":"facilitator","path":"/glossary/facilitator"},{"slug":"coinbase-cdp","title":"Coinbase Developer Platform (CDP)","path":"/glossary/coinbase-cdp"},{"slug":"x402-org-facilitator","title":"x402.org facilitator","path":"/glossary/x402-org-facilitator"}],"terms_used":["facilitator","coinbase-cdp","x402-org-facilitator"],"last_reviewed":"2026-08-27","review_hash":"b772cb5c4940c9b7","url":"https://probe402.com/glossary/catalogue"},"requested_entry_problem":null}