The Universal Commerce Protocol (UCP) is a protocol for letting AI agents buy things through one pattern rather than one integration per merchant. As described in Developer’s Guide to AI Agent Protocols, it standardizes the shopping lifecycle into modular capabilities, expressed as strongly typed request and response schemas that remain consistent whatever the underlying transport — REST, Model Context Protocol, Agent2Agent Protocol (A2A), or Embedded Protocols (EP) for browser-based flows.
Usage
The problem UCP addresses, in that guide’s framing, is that every supplier has a different checkout
API, so an agent sourcing from five wholesale distributors would otherwise need five different checkout
integrations. With UCP, the agent discovers a merchant’s capabilities from a profile published at a
well-known URL (/.well-known/ucp) — the same discovery pattern A2A uses for its Agent Cards — then
builds a typed checkout request with line items and payment details, creates a checkout session, and
completes it. The guide’s example sends identifying headers with each request, including one pointing
to the calling agent’s capability profile and a fresh idempotency key per operation.
Because UCP also supports a standard REST API, the guide notes that it works with whatever HTTP client a project already uses, with no proprietary SDK required. It also points to a sample shopping assistant that combines UCP with A2A for end-to-end shopping workflows.
UCP covers what is ordered and from whom. Authorization for the purchase — who approved it, within what limits — is the job of the Agent Payments Protocol (AP2), which the guide describes as plugging into UCP as an extension.
Related Terms
- Agent Payments Protocol (AP2) — adds payment authorization and an audit trail to UCP’s checkout flow
- Agent2Agent Protocol (A2A) — whose well-known-URL discovery pattern UCP reuses
- Model Context Protocol — one of the transports UCP can run over