Checkout Security: Strict Limits, Checkout Validation and the Checkout Extension

MinCart has three ways to check your limits at checkout. Two of them are older and stay only for the limits that aren't strict:

Strict limits block every way to check out. The one exception: a limit that checks many tags and collections can show a large-cart warning, and Shopify may skip its rule on carts larger than the size the warning names.

Table of Contents

1. Strict limits
2. Checkout validation (legacy)

• How to enable

3. Checkout extension (deprecated)

• How to remove it

Strict limits

Make a limit strict and MinCart registers it as one of your store's Shopify checkout rules. Shopify runs it in its own backend, at checkout, whatever way the customer got there. Turn the option on in the Strict limit section of each limit's page.

Strict limits work on every MinCart plan and every Shopify plan. Shopify allows 25 active checkout rules per store, across all apps, and each strict limit uses one. A few settings can't be strict. Everything is explained in Strict Limits.

Checkout validation (legacy)

Checkout validation is a checkout rule that passes on what MinCart's script found in the customer's cart: when a limit isn't met there, checkout stops. It doesn't check any limit itself, so it's only as reliable as the cart:

1. Only from your online store's cart: a checkout that doesn't come from the cart MinCart checked isn't stopped: Buy it now and express checkout buttons, cart links, abandoned cart emails, headless storefronts, other sales channels.
2. It can't stop bots, or a customer who changes their cart's data.
3. Checkout-only activation rules (shipping address, shipping type, shipping cost) never reach it: the cart can't read them.

It stays as a small extra safety net for limits that aren't strict. It does nothing for strict limits, which Shopify already checks, and it uses one of your store's 25 checkout rules while it's on. Prefer strict limits.

How to Enable Checkout Validation

[ Installation Video ]

1. Click on Shopify Settings
2. Click on Checkout
3. Scroll down to Checkout Rules
4. Click Add Rule

5. Select MinCart Checkout validation

6. Click on Save for the new rule.

7. Click on Turn On

Checkout extension (deprecated)

Strict limits are a new MinCart feature that replaces the checkout extension, and they're more secure: their rule runs on Shopify's servers, for every customer, signed in or not, with product types and every collection. If your checkout has MinCart's extension:

1. Make your limits strict, in the Strict limit section of each limit's page. The extension stops checking a limit as soon as it's strict, so its message never shows twice.
2. Fix the limits that can't be strict, if you can: each one's Strict limit section says why and how. See Strict Limits: What They Can't Check.
3. Remove the extension from your checkout (below).

MinCart's Home page lists the checkout extension in its App extensions box while it's in your checkout, with a Checkout editor button.

How to Remove the Checkout Extension

1. Click on Shopify Settings
2. Click on Checkout
3. Click on Customize next to your checkout profile.

4. Find the MinCart app block. With a one-page checkout, it's under Payment; with a three-page checkout, check the Information, Shipping and Payment steps.
5. Remove the block from each step where it appears.
6. Click Save.

Updated on: 19/10/2026