Action Required / API

Storefront MCP cart tools are being deprecated
Migration to UCP Cart MCP is required

Storefront MCP's get_cart / update_cart is being deprecated. Migrate to the UCP-compliant Cart MCP (new endpoint /api/ucp/mcp). The old tools remain available until August 31, 2026 .

On this page
  1. What's actually changing (understand it in 30 seconds)
  2. Old-to-new mapping diagram
  3. Old vs. new (Storefront MCP vs. UCP Cart MCP)
  4. What migration involves (4 steps)
  5. Points to watch out for (PUT semantics, etc.)
  6. 5 key points for developers
  7. 3 use cases you can apply to your work
  8. One-line summary for pitches

1What's actually changing

The MCP tools that let agents (AI) operate a store's cart aremoving from Shopify's proprietary Storefront MCP to the Cart MCP, which complies with the industry-standard UCP (Universal Commerce Protocol).
The old get_cart / update_cart will work until August 31, 2026, but after that all documentation will assume the new tools.
Deprecated

Old endpoint

https://{shop}.myshopify.com/api/mcp 's get_cart / update_cart is affected.

New endpoint

UCP Cart MCP

https://{shop-domain}/api/ucp/mcp. Implements the UCP cart features dev.ucp.shopping.cart(version 2026-04-08).

Deadline

August 31, 2026

The old tools are maintained until this date. Migration must be completed by then.

2Old-to-new mapping diagram

Old: Storefront MCP /api/mcp get_cart update_cart (no create / cancel) New: UCP Cart MCP /api/ucp/mcp create_cart Create a new cart with line items + buyer context get_cart Get the current cart state update_cart Replace the entire contents (PUT) cancel_cart Cancel the cart (requires idempotency-key) + Attach meta.ucp-agent.profile to every request
UCP(Universal Commerce Protocol)What it is: A common spec for AI agents to work with store carts across systems. This Cart MCP is the cart functionality of UCP dev.ucp.shopping.cart(version 2026-04-08). It adds what the old tools lacked, create_cart / cancel_cart covering the entire lifecycle.

3Old vs. new comparison

ItemOld: Storefront MCPNew: UCP Cart MCP
Endpoint https://{shop}.myshopify.com/api/mcp https://{shop-domain}/api/ucp/mcp
Tools 2 types get_cart / update_cart 4 types create / get / update / cancel
Compliant spec Shopify proprietary UCP dev.ucp.shopping.cart(2026-04-08)
meta object Not documented On every request, ucp-agent.profile is required. cancel also idempotency-keyneeds a (UUID).
Meaning of update Not documented PUT Full replacement (send all line_items every time)
Support deadline Until 2026-08-31 The future standard

4Migration steps (4 steps)

1

Swap the endpoint

get_cart / update_cart Point the calls to /api/ucp/mcp the Cart MCP tools.

2
meta

Attach meta to every request

ucp-agent.profile Always include it.cancel_cart For idempotency-keya (UUID) too.

3

Match the PUT semantics

update_cart is a full replacement. Every time the complete line_items arrayeach time.

4

Update the schema

Review the new request/response schemas for all cart tools and align your app.

For details, see the Cart MCP documentation(shopify.dev/docs/agents/carts-and-checkout/cart-mcp). The migration grace period runs until August 31, 2026 .

5Key things to watch

update is PUT = full replacement
not a per-field patch. Even to add a single item, you must send thecomplete line_items arrayevery time, including existing line items, or the cart is wiped.
cancel_cart requires an idempotency key
meta["idempotency-key"] Put a UUID in it. It's a safeguard against double cancellation on retries.

65 points engineers need to know

UCP

1. From Shopify-specific to the industry-standard UCP

Cart operations now conform to UCP dev.ucp.shopping.cart(2026-04-08). A move to align agent integration with a cross-vendor standard.

2 4

2. Tools expand from 2 to 4

The old set had only get/update. The new one adds create_cart / cancel_cart, covering the full cart lifecycle.

3. update is PUT (idempotent full replacement)

A state replacement, not a diff patch. You need to redesign the client to assemble the complete line items.

meta

4. meta requires an agent profile

on every request ucp-agent.profile. cancel also needs idempotency-key(UUID). Preparing a single shared request wrapper makes this easier.

5. The deadline is August 31, 2026 = Action Required

The old tools are maintained until this date, but after that all documentation assumes the new tools. Identify the endpoint URL (myshopify.com/api/mcp → {shop-domain}/api/ucp/mcp) and schema differences and switch over before the deadline.

73 use cases you can apply to your business

AI
USE CASE 1

Standards compliance for AI shopping assistants / agentic commerce

Problem
An AI concierge bot built on Storefront MCP's proprietary cart tools risks breaking on August 31.
Solution
Cart MCP(/api/ucp/mcp). Handle all cart operations with the four tools: create/get/update/cancel.
Impact
Becoming UCP-standard compliant makes it easier to connect with future agent integration targets (other tools and platforms).
Technical notes
In the shared request wrapper, meta.ucp-agent.profile is attached automatically. Only cancel generates and injects a UUID idempotency key.
USE CASE 2

Hardening cart sync logic with PUT semantics

Problem
The old implementation assumed incremental "add one item at a time" diffs, so moving to UCP's full-replacement PUT easily causes bugs where line items get dropped.
Approach
Keep the source of truth for cart state on the client, and rebuild and send the complete line_items array on every update.
Result
Cart contents stay intact even under concurrent updates or retries, keeping the sync idempotent.
Technical notes
Strictly follow the order: fetch the latest state with get_cart → merge locally → update with the complete array. cancel uses an idempotency-key to prevent double execution.
USE CASE 3

Present a deadline-driven migration plan to your team/clients

Problem
Across multiple apps/stores that integrate with the MCP cart, there's no inventory of who fixes what and when.
Approach
grep every repository for get_cart / update_cart call sites → list out the scope of impact → draw up a migration schedule working backward from 8/31.
Result
Avoid a production outage caused by missing the Action Required. Estimate the migration effort early.
Technical notes
Searching by the endpoint strings (/api/mcp) and tool names makes them easy to find. After migrating, add integration tests against the new schema to CI.

8A one-line summary you can use in a proposal

"The Storefront MCP cart tools (get/update) will be deprecated on August 31, 2026 .
You need to migrate to the UCP-compliant Cart MCP (/api/ucp/mcp, with 4 tools: create/get/update/cancel).
update is a full-replacement PUT, every request needs meta.ucp-agent.profile, and cancel requires an idempotency key—keep these three points in mind and switch over before the deadline."