Storefront MCP cart tools are being deprecated in favour of UCP Cart MCP

What's changing

The cart tools on the Storefront MCP server are being deprecated in favour of the UCP-conforming Cart MCP tools:

• get_cart and update_cart on https://{shop}.myshopify.com/api/mcp are deprecated.

Cart MCP implements the UCP cart capability (dev.ucp.shopping.cart, version 2026-04-08) and exposes the following tools at the https://{shop-domain}/api/ucp/mcp endpoint:

• create_cart: Create a new cart with line items and optional buyer context.
• get_cart: Retrieve the current state of a cart.
• update_cart: Replace the cart's contents.
• cancel_cart: Cancel a cart.

The deprecated tools will be maintained until August 31, 2026, but all documentation will refer to the Cart MCP tools.

What you should do

If you're building with the Storefront MCP cart tools:

• Migrate get_cart and update_cart calls to the Cart MCP tools, and update endpoints to use https://{shop-domain}/api/ucp/mcp.
• Include a meta object carrying ucp-agent.profile in every request, and a meta["idempotency-key"] (UUID) for cancel_cart.
• Note that update_cart uses PUT semantics: each request replaces the cart's full state, so send the complete line_items array on every update rather than patching individual fields.
• Consult the updated request and response schemas for all cart tools and update your app to match. See the documentation for Cart MCP (https://shopify.dev/docs/agents/carts-and-checkout/cart-mcp) for more details.