This guide describes how to integrate with the Universal Commerce Protocol (UCP) Cart API, allowing users to build and manage a shopping cart across Google surfaces, including AI Mode in Google Search and Gemini. This capability is designed for basket building before the user has expressed explicit intent to check out.
Overview
The UCP Cart API (Capability Name:
dev.ucp.shopping.cart
) enables the transfer of a user's shopping cart from Google surfaces, such as
AI Mode in Google Search and Gemini, directly to your website. This API supports
Google's Universal Cart feature by allowing a one-way population of the cart on
your system, primarily through the CreateCart endpoint.
This initial release is limited to cart creation and transfer using the
CreateCart method. Features like updating, deleting, or synchronizing cart
contents between Google and your system are not supported.
Key Benefits
Key Benefits of Implementing CreateCart:
- For Users: A seamless transition from product discovery on Google to a prepopulated cart on your website.
- For Merchants: Receive user carts directly from Google, simplifying the initial purchase steps for customers and providing opportunities for upselling and cross-selling on your website.
Prerequisites
- Ensure your system is set up to handle UCP version
2026-04-08. - Publish your UCP profile at
/.well-known/ucpand include thedev.ucp.shopping.cartcapability, as described in the UCP Profile guide. Theendpointspecified in your profile (for example,https://business.example.com/ucp/v1) will be used as the base URL for these API calls.
Authentication
For details on securing your Cart API endpoints, including supported authentication methods like API keys and OAuth 2.0, see the Authentication & Security guide.
Service level objectives and capacity planning
While formal Service Level Objectives (SLOs) are not enforced for the
POST /carts endpoint, we strongly recommend that you meet the following
targets to ensure a seamless cart transfer experience for users:
- Latency: respond as quickly as possible, ideally in under one second. Responses taking longer than one second don't cause the transfer flow to fail, but higher latency can degrade the user experience.
- Capacity planning: plan your endpoint capacity according to the referral
traffic you expect during your peak campaigns. The
POST /cartscalls are driven entirely by user intent (triggered when a user clicks to transfer their cart) and request volume is based on user traffic. - Rate limiting: gracefully throttle requests by returning standard
HTTP 429 (Too Many Requests)responses if your system receives traffic that exceeds its rate limits. For more information, see Error codes.
Next steps
View the API payloads and technical implementation details for the UCP Cart API: