UCP Cart Capability

Before writing code

Fetch live spec: Web-search site:ucp.dev specification shopping cart and fetch the page for the exact Cart schema, operation names, and binding details. Also fetch https://ucp.dev/latest/schemas/shopping/cart.json for the authoritative JSON Schema. Field names and required-ness change between spec versions — never write the schema from memory.

Conceptual Architecture

Why Cart is separate from Checkout

Checkout carries payment handler configuration, buyer commitment, and a status lifecycle. That is overhead a buyer does not need while still browsing. Cart is the lightweight half: collect items, get estimated totals, share a link — with no payment configuration and no status machine.

The canonical progression is:

cart session  →  checkout session  →  order

Cart handles exploration. Checkout enforces commitment.