When stock is limited, the risk is one buyer taking all of it. A cart cap spreads limited inventory across more customers.
Before you start
- The most items a single order should contain.
- Whether a per-product cap would serve you better — it usually does for a single hyped item.
Steps
1. Install Nex Validator
Search Nex Validator in the Shopify App Store, or use the button below. Approve the permissions and the app appears in your admin under Apps. There is a free trial, and it works on every Shopify plan.
2. Go to Simple Order Limit → Create Rule.
3. Give the rule a title, and switch Enable/Disable Limit on. A rule that is saved but not enabled looks identical to one that is not working.
4. Open the Cart tab, choose Cart Max Quantity, and enter the maximum number of items.
5. Write the message, then save. Explain why, briefly — “Limit 2 per order so everyone gets a chance” converts better than a bare rejection.
Verify it worked
- Cart above the cap → checkout blocked.
- Cart at the cap → checkout completes.
Common setups
| Goal | Maximum |
|---|---|
| Flash sale fairness | 2–4 items |
| Ticketed events | Your per-person allowance |
| Regulated products | Whatever your rules require |
| Protecting a restock | 1–2 items |
Set it too low and you block genuine bulk customers. If you have wholesale buyers on the same storefront, consider Advanced rules so the cap applies only to retail customers.