How a purchase completes.

What a checkout API call looks like from the other side.

Strip away the protocol names and an AI agent completing a purchase is, from a business's own system, just another API request arriving with a specific, checkable shape. Here's roughly what lands, and what a business's system has to do with it.

UCP and the checkout handoff: what changes when a purchase completes inside the conversation.

Every other protocol in this hub gets a purchase ready. UCP is the one that completes it: the point where a business hands back a confirmed order without sending the customer off to finish the job on a website.

MCP, explained: what it actually connects, and what it doesn't.

Model Context Protocol gives an AI agent a standard way to call into a business's own systems: read live data, run a search, trigger a defined action. It has nothing to do with payment or identity. That's a separate job, done by separate protocols.

Holds, mandates and spend limits: how a business keeps control of an automated payment.

A mandate only says what an AI agent was allowed to try. What protects a business is what happens on its own side of the transaction: the hold it places, the ceiling it enforces, and the mandate scope it insists on before a booking or order is allowed to proceed.

AP2 and agent payments: how an agent proves it's allowed to spend on someone's behalf.

A credential proves an AI agent is who it says it is. AP2 (Agent Payments Protocol) proves something narrower and more specific: that a real person authorised this exact spend, up to this exact limit, and a business can verify that before it charges anything.

Agent credentials: the token that says "yes, actually let this agent buy."

Before an AI agent can act on anyone's behalf, something has to vouch for it. An agent credential is the short-lived, scoped proof a business checks before it trusts a request enough to act on it.

A2A, explained: how one agent proves what it's asking another to do.

A shopping AI agent rarely finishes the whole job itself. It hands specific tasks to other, more specialised agents along the way. Agent2Agent protocol is how one agent describes a task to another clearly enough that the second agent can trust it and act on it.