Building High-Converting Custom Checkout Experiences

Shopify's transition to Checkout Extensibility allows developers to safely customize checkouts using UI Extensions. This transition offers security benefits but changes how we design custom flows.

Modern Customizations

Checkout UI extensions operate in sandboxed environments, which means we cannot inject arbitrary scripts. Instead, we:

• Use pre-built UI Components provided by Shopify's SDK.
• Connect checkout data to external APIs using secure, authorized fetch calls.
• Run light validation logic locally at checkout runtime.

This approach guarantees checkout pages remain lightning-fast and upgrade-safe while allowing customizable discount upsells and address validators.