# 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.

August 22, 2026 · Updated September 21, 2026 · Sources checked September 21, 2026

https://app.ai-commerce-ready.com/blog/shopify-storefront-mcp-cart-tools-deadline-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]

## What this cannot prove

An inventory and passing tests do not guarantee uptime or live orders. The checked Shopify pages do not establish whether deprecated calls still work on your store or the time they stop. [1][3]

## Paid help and free options

- When paid help makes sense: Paid help has a defined task when a custom integration you use still calls the deprecated cart tools and its owner must migrate and test it. A quote without affected calls does not establish work you need. [1][2]
- What’s already free: Shopify publishes the migration instructions and Cart MCP reference. You do not need a paid monitoring product to learn which calls the integration owner must inspect. [1][2]

**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](https://shopify.dev/changelog/storefront-mcp-cart-tools-are-being-deprecated-in-favour-of-ucp-cart-mcp) 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](https://shopify.dev/docs/apps/build/storefront-mcp/servers/storefront) 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](https://shopify.dev/docs/agents/carts-and-checkout/cart-mcp) requires:

1. The new endpoint and `meta["ucp-agent"].profile` on every request.
2. The complete desired cart on `update_cart`. It replaces the cart; resend unchanged items and required attribution.
3. A UUID in `meta["idempotency-key"]` on `cancel_cart`.
4. 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.

## Sources

1. [Storefront MCP cart tools deprecation](https://shopify.dev/changelog/storefront-mcp-cart-tools-are-being-deprecated-in-favour-of-ucp-cart-mcp)
2. [Cart MCP](https://shopify.dev/docs/agents/carts-and-checkout/cart-mcp)
3. [Storefront MCP server](https://shopify.dev/docs/apps/build/storefront-mcp/servers/storefront)