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)

Sources (2)

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

  1. x402Payment over HTTP 402The seller’s 402 challenge carries the ATR hash and a link to the ATR; the payment carries the ATR hash in the rail’s own field.29 pairings in @integraledger/lcp
  2. MPPMachine Payments ProtocolThe MPP challenge itself carries the ATR hash: its id is derived from it, so whatever the payer signs over the challenge commits to it.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 pairings in @integraledger/lcp
  6. ACKAgent Commerce KitThe seller-signed Payment Request takes the ATR hash as its id.1 pairings in @integraledger/lcp
  7. Visa TAPTrusted Agent ProtocolThe agent’s payer signature covers a field holding the ATR hash.1 pairings 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 carries the ATR hash in its own pairing.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