Shopify Glossary Terms

Checkout UI Extensions are sandboxed React components that render within Shopify's checkout. They're the presentation layer of Checkout Extensibility - the way you add custom visual elements to the checkout flow on Shopify Plus.

Extensions render at defined target locations within checkout - before and after the contact information, shipping method, payment method, and order summary sections. You can also render extensions on the thank-you page and order status page.

They're sandboxed, which means they run in an isolated environment without access to the full DOM. This prevents scripts from breaking checkout but limits what you can do visually. Shopify provides a UI component library (Polaris for checkout) that ensures extensions match the checkout's look and feel.

Common extensions include custom form fields, upsell product cards, loyalty point displays, delivery date pickers, and gift message inputs. For the full picture, see our checkout customisation guide.

Think: the building blocks for a checkout that does more than just take payment.