Do I need Storefront MCP cart migration, and what should I verify before paying for it?
Ask for affected calls before paying. Updated carts must preserve other items and attribution; cancellation and checkout need tests.
· Updated September 21, 2026
- When this applies
- You run or pay for a custom shopping agent, assistant, or integration, or a vendor has quoted Storefront MCP cart migration work. [1] [2]
- When this does not apply
- No migration is needed when the integration owner confirms that nothing you run or pay for calls get_cart or update_cart at /api/mcp. Standard Shopify storefront use alone is outside this migration. [1] [2]
- Why this matters
- Shopify’s stated maintenance window for the old cart tools ended on August 31, 2026. Their replacement overwrites the full cart on update, so an endpoint-only migration can discard unchanged items and attribution. [1] [2]
- What to do
- Ask the owner to list the endpoints and tools. Migrate affected /api/mcp cart calls and require dated tests for full-cart updates, cancellation, and checkout handoff. With no affected calls, decline the migration. [1] [2]
- When you’re done
- You have written confirmation that no affected integration exists, or an inventory showing no old /api/mcp cart calls plus dated tests showing updates preserve unchanged items and required attribution, cancellation makes the cart unavailable, and the integration’s checkout handoff works. [1] [2]
- Sources checked
- September 21, 2026
Paid help and free options
Only custom integrations using the old cart calls need migration. Ask the integration owner for the endpoint and tool list before approving a quote.
Identify the calls
Shopify’s deprecation notice names get_cart and update_cart at https://{shop}.myshopify.com/api/mcp. Shopify set August 31, 2026 as the maintenance end date; the replacement is https://{shop-domain}/api/ucp/mcp.
Match both endpoint and tool. search_shop_policies_and_faqs is not a cart-migration task merely because it uses the old endpoint.
The Storefront MCP reference still listed old cart tools when checked September 21, 2026. That historical listing and the elapsed date establish neither support nor live call behavior.
If there are no affected calls, keep written confirmation and decline this migration. Standard Shopify storefront use alone needs no change.
Give the developer the full requirements
The Cart MCP reference requires:
- The new endpoint and
meta["ucp-agent"].profileon every request. - The complete desired cart on
update_cart. It replaces the cart; resend unchanged items and required attribution. - A UUID in
meta["idempotency-key"]oncancel_cart. - Validation against current request/response schemas and the integration’s checkout handoff.
Check a dated test record
Use several cart items. Adding, changing quantity, and removing one must preserve the other intended items and attribution. Test Checkout MCP handoff separately if used.
cancel_cart removes the cart. A later get_cart for its ID must return not_found; cancelled carts need not retain items.
Finish with no old cart calls and passing dated tests, or written confirmation that no affected integration exists. The record covers that integration, not uptime or live-order guarantees.