Shopify Checkout Extensibility is the framework that allows Shopify Plus merchants to customise the checkout experience using official, supported APIs - specifically Checkout UI Extensions and Shopify Functions. It replaced the deprecated checkout.liquid customisation method in 2024 and is the only supported way to modify the Shopify checkout on Plus plans going forward.
Checkout Extensibility solves a fundamental tension in Shopify's architecture: Shopify controls and optimises the checkout for conversion and payment security, but merchants need to add their own elements - loyalty point redemption, custom upsells, gift message fields, custom shipping logic, branded content - without compromising checkout performance or security. Checkout UI Extensions allow approved third-party app blocks to be inserted at defined points in the checkout flow. Shopify Functions allow merchants to write custom server-side logic that runs within Shopify's infrastructure to modify discounts, delivery options, and payment methods.
Common customisations include: displaying and redeeming loyalty points at checkout (through apps like LoyaltyLion or Smile.io); post-purchase upsell pages (the thank-you page after purchase); custom gift message or personalisation fields; showing subscription upgrade offers at checkout; and custom discount validation logic. The Checkout Extensibility framework has made many of the complex checkout customisations that previously required a headless Shopify build accessible to standard Shopify Plus stores, significantly reducing the business case for going headless solely for checkout customisation reasons.
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