Per-customer limits
One per customer, checked at checkout.
For a limited drop or a Black Friday doorbuster, a maximum per cart is not enough: the same buyer can check out twice. A per-customer limit counts what that customer already bought. This page covers how the count works, what to do about guests, and where Shopify enforces it.
Per cart or per customer
A per-cart rule, such as no more than 2 of one product per order, looks only at the cart in front of it. A per-customer rule adds the units that customer account has already ordered, so a second order for the same product is blocked as well. A minimum purchase is a different rule; see wholesale minimum order rules for customer-tag and first-order minimums.
Guests: allow them or require an account
A guest checkout has no customer account, so there is nothing to count against. You choose between two setups:
- Guests allowed. Account holders are limited to one unit per product. Guests are not counted and can check out, which keeps checkout open but lets a determined buyer order again as a guest.
- Account required. Checkout must be linked to a customer account, and each account is limited to one unit per product. Rulestage checks the account link on the checkout, not how the buyer signed in.
Both setups are templates in the app. Pick one, adjust the limit and the products it covers, and test it before it goes live.
How the count works
Rulestage adds each order's units to the customer's history when Shopify reports the order. It counts orders placed after Rulestage is installed; earlier orders are not imported. The history update can lag a few seconds, so two checkouts placed back to back by the same customer may both pass.
Where the limit is enforced
Rules run in Shopify's server-side checkout validation, so a cart over the limit can't complete checkout. That covers the online-store cart and checkout, Shop Pay, PayPal, Google Pay and Apple Pay, the Storefront API, and B2B and draft-order checkouts. Shopify does not run validation on POS, order editing, the orderCreate API, subscription renewals or pre-orders, so no app can enforce a limit there.
Test a cart before the sale starts
Build a cart, choose a buyer with or without an account and with earlier orders, and run it against your draft rules. The result names the rule that blocked it and the message the buyer sees. On Guard, you can roll back to an earlier version after the sale.
Price
Build rules and simulate your own carts free, without enforcement. Enforce is $9 a month for checkout enforcement. Guard is $29 a month and adds conflict review, scenarios and version history. Both have a 14-day trial, then Shopify bills monthly unless you cancel.