What Are Checkout Extensions in Shopify Plus
Checkout Extensions are Shopify's official API for customizing the checkout flow without modifying the checkout.liquid file — which was discontinued in August 2024 for most Shopify Plus stores.
The change was significant: previously, development teams directly modified the checkout HTML/Liquid, which was powerful but fragile — any Shopify update could break customizations. With Checkout Extensions, customizations are built using the Checkout UI Kit (React + Shopify APIs) and run in the same secure environment as the native checkout.
Important: Checkout Extensions require Shopify Plus. On Basic, Shopify or Advanced plans, the checkout is fixed and cannot be customized beyond the admin settings.
What Is Possible with Checkout Extensions
The Checkout Extensions API allows adding visual components and custom logic at specific points in the checkout. The main use cases are:
Post-purchase Upsell and Cross-sell
Offer complementary products on the order confirmation screen with one click to add without re-entering payment data.
Custom fields
Add information fields to the order: gift message, desired delivery date, corporate reference number (B2B).
Address validation
Integrate zip code APIs for automatic filling, validate delivery addresses in real time or block specific regions.
Custom payment methods
Display installment banners, BNPL (Buy Now Pay Later) calculators and dynamic shipping information based on the cart.
Real Limitations That Apps Promise to Solve but Cannot
There is a narrative in the market that "apps solve everything in Shopify Plus checkout". In practice, there are structural limitations that even expensive apps cannot work around:
What Even Apps Cannot Do
- Modify the native checkout flow — you cannot re-order steps (address → shipping → payment) or remove steps from the standard flow
- Access raw payment data — for PCI DSS reasons, no extension accesses card number or CVV
- Execute complex backend logic in real time — validations that need access to slow external systems can cause timeouts
- Customize the order confirmation email via Extension — this requires Shopify Email or separate templates
What Apps Generally Promise but Deliver Poorly
"Checkout customization" apps frequently use iframes or overlays that load slowly, break on mobile, conflict with payment methods or are disabled by Shopify updates. An extension natively developed with the Checkout UI Kit is more stable and faster.
Red flag: Any app that promises "checkout customization" without being built on the official Checkout Extensions API probably uses fragile solutions that can break on Shopify updates. Check if the app uses checkout_ui_extension in the public API.
When to Use Checkout Extensions vs. Apps
| Scenario | Native Checkout Extension | Shopify App Store App |
|---|---|---|
| Simple post-purchase upsell | ✅ Ideal — fast and integrated | ✅ Apps like Reconvert work well |
| B2B custom fields | ✅ More reliable and direct | ⚠️ Depends on the app — test each one |
| Real-time ERP integration | ✅ Via Functions + webhooks | ❌ Apps rarely support ERP latency |
| Visual layout different from default | ⚠️ Limited to the design system | ❌ Not possible even with apps |
| Complex discount rules | ✅ Via Shopify Functions | ⚠️ Limited depending on discount type |
Shopify Functions: The Most Powerful Part
Beyond visual extensions, Shopify Plus offers Shopify Functions — backend logic that runs on Shopify's infrastructure to customize discount rules, delivery methods and payment rules.
With Shopify Functions you can:
- Create fully custom discount rules (e.g. "buy X products from collection Y and earn Z% on the next purchase")
- Hide delivery methods based on business logic (weight, zip code, order value, customer tags)
- Hide payment methods based on custom criteria (e.g. show bank slip only for B2B customers)
- Create gift cards and promotions with rules that Shopify's native admin does not support
Need to implement customizations in your Shopify Plus checkout?
I develop native Checkout Extensions and Shopify Functions for Shopify Plus stores. Stable implementations, without relying on fragile apps, using Shopify's official APIs.