What is UCP?
Universal Commerce Protocol (UCP) is an open standard that lets AI agents shop on behalf of users — searching catalogs, adding items to carts, and completing checkouts programmatically.
The Problem
Today's e-commerce is built for humans clicking buttons. AI agents need structured, machine-readable interfaces to browse products, compare options, and transact. Without a standard protocol, every store requires custom integration code.
How UCP Solves It
UCP defines a set of capabilities that any store can implement. An AI agent connects to a store's UCP endpoint and uses standard operations. Exact tool names vary a little by store and transport; typical ones are:
- search_catalog — Search products with filters, pagination, and sorting (Shopify's older storefront endpoint calls it
search_shop_catalog) - lookup_catalog / get_product — Fetch full product info including variants, pricing, and availability
- create_cart / update_cart — Manage shopping carts with line items
- create_checkout / update_checkout / complete_checkout — Handle the full checkout flow including payment
The specification is versioned by date. The current releases are 2026-08-25 (latest) and 2026-04-08.
Transports
A store can declare four transports in its manifest — the ways an agent connects:
- MCP (Model Context Protocol) — JSON-RPC over HTTP for tool calls. The primary transport for AI agent interactions.
- REST — Standard HTTP endpoints, for stores that serve UCP as an HTTP API.
- A2A — Agent-to-agent: the store side is itself an agent rather than a tool server.
- Embedded — the Embedded Checkout Protocol (ECP): the store hands its checkout UI to the host application at the payment step (iframe plus MessagePort handshake), for payment flows that need a browser context.
UCP Playground connects over MCP and REST, opens embedded checkouts, and shows A2A as declared.
Some stores also register tools on their own web pages through WebMCP. That is a separate route, not a UCP transport. The Playground can run an agent through it and set it beside the store's UCP tools; see WebMCP: the store page.
What is UCP Playground?
UCP Playground is a testing and observability tool for UCP. It lets you:
- Inspect — In the Inspector, connect to any UCP-compatible store, browse its tools, and call them manually to debug responses; the WebMCP view shows the store page's own tools beside them
- Benchmark — On the Agent page, run AI models (Claude, GPT, Gemini, and more) against your store over UCP, or through the store page's WebMCP tools, and measure how far they get
- Compare — Test multiple models side-by-side to find which handles your catalog best
- Replay — Every session is saved as a replay: the chat view and the wire-level Backend view, shareable and embeddable
- Audit — View published UCP compliance scores across manifest, runtime, and gap consistency on the UCP Checker Leaderboard
New to UCP Playground? Start with the Quick Start guide to run your first agent session in under five minutes.
Discovery
Stores advertise their UCP support through a discovery manifest at /.well-known/ucp. This JSON file tells agents which UCP version the store runs, which transports it serves and where, what capabilities it declares, and what payment methods it accepts.
UCP Playground reads this manifest automatically when you enter a domain, so you can immediately see what a store supports before running any tests.