Cart API

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.

Note: This Cart API is a new feature and is only available starting with UCP version 2026-04-08.

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 API is distinct from the Checkout API, as it does not handle payments or the full purchase lifecycle.

Note: 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 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/ucp and include the dev.ucp.shopping.cart capability, as described in the UCP Profile guide. The endpoint specified in your profile (for example, https://business.example.com/ucp/v1) will be used as the base URL for these API calls.

Next steps

View the API payloads and technical implementation details for the UCP Cart API:

• Version 2026-04-08 Cart API