UCP
UCP — the Universal Commerce Protocol — describes itself as a common language for platforms, agents and businesses: building blocks for agentic commerce from discovery through checkout. It is assembled from transports and agent standards that already exist rather than defining its own.
The site states the shape plainly — building blocks for agentic commerce across industries, from discovery to checkout and beyond, so that the ecosystem can work through one standard without custom builds. It names its foundations as REST and JSON-RPC transports, with support built in for AP2, for A2A — the agent-to-agent protocol — and for MCP.
It is co-developed rather than published by a single party, and the roster is on its own site. What matters for vocabulary is the lane it occupies, which is the one ACP occupies. Stripe's integration guidance points a seller who wants to sell through agents at UCP or ACP, and a seller who wants to charge for an API somewhere else entirely.
For a glossary of machine payments it is a boundary marker. UCP is about commerce between businesses and agents — catalogues, carts, checkouts — and says nothing about HTTP 402. An endpoint charging for each call is not doing what UCP describes, even when an agent is the one paying.
→ probe402 measures the machine-payment rails rather than the commerce protocols, and the boundary it works to is set out in the method.
Sources
- The Universal Commerce ProtocolUniversal Commerce Protocol
- Agentic commerceStripe documentation
Related agentic commerce · ACP · AP2 · MCP