Shopify Glossary Terms

Checkout extensibility is Shopify's framework for customising the checkout experience on Shopify Plus. It replaced the old checkout.liquid approach (which gave merchants raw access to the checkout template) with Checkout UI Extensions - sandboxed React components that Shopify hosts and renders within the checkout flow.

What you can do with it: add custom fields (gift messages, delivery instructions), in-checkout upsells and cross-sells, post-purchase one-click offers, loyalty point redemption, branding customisation (colours, fonts, logos), and payment/shipping logic via Shopify Functions.

What you can't do: fundamentally change the checkout layout, inject arbitrary JavaScript, or override Shopify's payment processing. These limitations are intentional - they protect conversion rates and security.

The trade-off is less raw power for significantly more stability. Your checkout won't break because a third-party script conflicts with a Shopify update. Read our full checkout customisation guide for what's actually possible.

Think: the framework that lets you customise checkout without ever breaking it.