By protocol

The agreement rides the protocols agents already speak.

Each protocol below is someone else’s work. Each page says, in the standard’s and the package’s words, where the ATR hash rides in it, what the buyer signs, and what a payment through it proves. Source: LCP Appendix C⁠ (opens in a new tab) · Source: lcp docs: agentic checkouts⁠ (opens in a new tab) The Agentic Transaction Record (ATR) is one record of exactly what was agreed, for one transaction. Its ATR hash, the ATR’s fingerprint, is the proof bound to the transaction: change one byte of the ATR and it no longer matches. Source: lcp docs: the ATR⁠ (opens in a new tab) · Source: lcp docs: the ATR hash⁠ (opens in a new tab)

LCP Appendix C⁠ (opens in a new tab) · lcp docs: agentic checkouts⁠ (opens in a new tab) · lcp docs: the ATR⁠ (opens in a new tab) · lcp docs: the ATR hash⁠ (opens in a new tab)

  • x402Payment over HTTP 402The seller’s challenge: The ATR hash and a link to the ATR, in extensions.legalContext.
  • MPPPayment in HTTP authenticationEvery MPP challenge: Its id is the ATR hash itself, with a link to the ATR beside it.
  • ACPAgentic checkoutThe checkout session: Its id is the ATR hash; its metadata carries the link to the ATR.
  • UCPCommerce lifecycleThe checkout: A legal_context link carrying the ATR hash, before the business signs the checkout.
  • AP2Payment mandatesThe merchant’s signed checkout: The ATR hash, as its legalContext.
  • ACKAgent identity and paymentsThe seller’s signed Payment Request: Its id is the ATR hash.
  1. x402Payment over HTTP 402The seller’s 402 challenge carries the ATR hash and a link to the ATR; on most rails, the payment then carries the ATR hash in a field the rail already has.29 pairings in @integraledger/lcp
  2. MPPMachine Payments ProtocolThe MPP challenge’s id is the ATR hash itself, with a link to the ATR beside it; on many of MPP’s payment methods, the payer’s signature covers the ATR hash too.26 pairings in @integraledger/lcp
  3. ACPAgentic Commerce ProtocolThe checkout session’s id is the ATR hash, with the link to the ATR in the session’s metadata.2 pairings in @integraledger/lcp
  4. UCPUniversal Commerce ProtocolA legal_context link in the checkout carries the ATR hash, before the business signs the checkout.4 pairings in @integraledger/lcp
  5. AP2Agent Payments ProtocolThe merchant-signed checkout carries the ATR hash, and the buyer’s Checkout Mandate commits to that checkout.1 pairing in @integraledger/lcp
  6. ACKAgent Commerce KitThe seller-signed Payment Request takes the ATR hash as its id.1 pairing in @integraledger/lcp
  7. Visa TAPTrusted Agent ProtocolWhen the agent lists an lcp-hash field holding the ATR hash among the components it signs, its payer signature covers the ATR hash.1 pairing in @integraledger/lcp
  8. Verifiable IntentMastercard Verifiable IntentA Verifiable Intent mandate signs the hash of a checkout that carries the ATR hash.2 pairings in @integraledger/lcp
  9. A2AAgent2Agent protocolA2A delivers the ATR hash and a link to the ATR with the task; the payment for the task binds it as that payment’s own pairing does.delivery, no pairing
  10. MCPModel Context ProtocolMCP delivers legal context to agents as tools, whatever protocol the payment uses.delivery, no pairing

Every payment type in the package: where the ATR hash rides, and what each proves

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