Checkout used to be the one place on a Shopify Plus store where the developer with checkout.liquid access held all the cards. Checkout extensibility changed that. Customization now happens through apps, configurable blocks, and Shopify's own APIs, which makes changes safer and faster. It has not made it any easier to decide which changes are worth making.
What It Covers
Checkout extensibility is Shopify's framework for customizing checkout and the Thank you and Order status pages without editing checkout code directly. It includes checkout UI extensions (app blocks for custom fields, upsells, trust badges, and messaging), Shopify Functions (custom logic for discounts, delivery and payment options, and cart validation), branding controls, and web pixels for tracking. Extensions are upgrade-safe and work with Shop Pay.
checkout.liquid is no longer supported for the Information, Shipping, and Payment steps, and Shopify sunset checkout.liquid and additional scripts on the Thank you and Order status pages for Plus stores on August 28, 2025. Any Plus brand still relying on legacy checkout customizations or scripts should already have migrated.
Why It Needs a Real Owner
Because so much can now be installed from an app, checkouts collect extensions the same way storefronts collect widgets. Every block adds something for the shopper to process at the most sensitive step in the funnel. Tracking also needs attention, since analytics and ad platform events now flow through web pixels and customer events rather than scripts pasted into checkout. Someone needs to own the checkout as a system, not as a list of installs.
Who Should Own It
Checkout belongs with an eCommerce Developer or Technical Lead, working closely with the CRO owner who decides what to test. Many simple changes can be made in the checkout editor, but custom UI extensions and Shopify Functions require development. Whether that developer is in-house, fractional, or an agency depends on how often the brand changes its checkout.
What to Screen For
- Hands-on checkout UI extension and Shopify Functions work, not just theme development.
- Migration experience moving a store off checkout.liquid and legacy scripts.
- Tracking implementation through web pixels and customer events.
- A test-first mindset, working with CRO on what to change rather than building whatever is requested.
A strong answer names specific customizations and the extension, Function, or process change that replaced each one. A candidate who has not done a migration will struggle to be concrete.
Frequently Asked Questions
Do I need a developer for Shopify Plus checkout extensibility?
For simple changes, often not, since many apps and branding settings work through the checkout editor. Custom checkout UI extensions and Shopify Functions for discounts, delivery, payment, or validation logic do require development.
Should a Shopify Plus checkout developer be in-house or an agency?
Brands making frequent checkout changes usually get more value from a dedicated in-house or fractional developer. Brands making occasional changes are often better served by a specialized agency or freelancer on an as-needed basis.
More Shopify Plus Apps
For how all of these fit together, and which roles to hire at each growth stage, see The Top Shopify Plus Apps for 2026, and the eCommerce Talent You Need to Run Them, or browse the full Shopify Plus apps guide.