Shopify’s checkout is famous for its speed and high conversion rates, but merchants often need extra fields, loyalty perks or post‑purchase upsells. Historically, Shopify Plus stores customized the checkout.liquid file to add banners and scripts. That method is now deprecated and will stop working by January 2026. To future‑proof your store, you need to embrace Shopify Checkout Extensibility. This new framework lets you personalize the entire checkout experience with apps, blocks, pixels and Shopify Functions. Better yet, Shopify Checkout Extensibility is upgrade‑safe, meaning your customizations will continue working as Shopify rolls out one‑page checkout, Shop Pay improvements and other innovations.
Why Shopify is deprecating checkout.liquid
Until recently, Plus merchants could edit the checkout.liquid theme file to insert analytics scripts, custom fields and UI tweaks. This method had serious downsides: merchants carried the burden of maintaining and debugging their custom code, and it often conflicted with Shop Pay and new features. Shopify announced that the old approach will be shut down on August 13 2024 for checkout customizations, and automatic upgrades for Thank you and Order status pages begin in January 2026. By moving to Checkout Extensibility, merchants get a standardized, secure sandbox environment controlled by apps rather than brittle theme edits.
What is Shopify Checkout Extensibility?
Checkout Extensibility is a suite of upgrade‑safe tools—UI extensions, Shopify Functions and pixels—that replace checkout.liquid. With these tools you can customize every stage of checkout:
UI extensions allow merchants to insert custom components at specific extension points during checkout. You can customize product information, shipping options, payment methods and the order summary. This capability is currently available for information, shipping and payment steps on Shopify Plus and for Thank you and Order status pages on all plans.
Shopify Functions let developers write server‑side business logic—such as discount rules, shipping rate adjustments or payment method sorting—that runs within Shopify’s infrastructure. These functions replace Shopify Scripts, which will end support in June 2026, and run up to 100× faster.
Pixels provide a way to track customer behaviour without injecting scripts. You can collect events like “add to cart,” “add payment info” and “purchase” across checkout and post‑purchase pages. Pixels are more secure and easier to manage than manually inserted scripts.
Key benefits of Checkout Extensibility
Rootsyntax’s 2025 guide summarizes why extensibility is superior to checkout.liquid. It highlights that changes are modular, secure and upgrade‑safe, can be installed via apps without touching theme files, support both checkout and post‑purchase pages, and work with Shop Pay. Additional benefits include:
Compliance – The new framework offers better PCI and international regulation support.
Seamless Shop Pay integration – Customizations built with extensions automatically work with Shop Pay, which converts up to 50 % better than guest checkout.
Performance and security – Extensions run in a sandbox and are loaded by Shopify, eliminating the need for insecure scripts.
Future‑proof – Apps built with Checkout Extensibility automatically get new features like Shop Pay enhancements, one‑page checkout and discount stacking.
What’s new in 2025
Shopify continues to expand Checkout Extensibility, adding capabilities in 2025 that make customization easier and more powerful. According to Rootsyntax’s update, notable additions include:
UI Extensions for Checkout – Add custom banners, form fields, offers or modules at specific points in the checkout flow. These extensions can also access buyer context (e.g., cart items or shipping method) via App Bridge Checkout.
Post‑Purchase Page APIs – Create dynamic upsells or referral workflows on the Thank you page.
Custom Validation API – Enforce business rules like PO Box restrictions or B2B‑only shipping with server‑side validation.
Function APIs for Discounts & Delivery – Use functions to control discount logic, shipping rules and available payment methods.
Global Field Input Blocks – Collect additional customer details such as tax IDs or gift messages without editing templates.
These innovations demonstrate that Shopify is turning checkout into a composable platform. You can choose from a growing ecosystem of extensibility‑powered checkout apps or build your own, ensuring your customizations stay compatible with Shopify’s releases【401689370567853†L170-L169】.
Design customization with Checkout Branding
One of the first tasks when customizing checkout is aligning its look with your brand. Shopify’s new Checkout Branding tools let merchants change the logo, background, colors, fonts and element shapes through a drag‑and‑drop editor. Developers can go further by:
Applying custom fonts and adjusting sizes of headings and form inputs.
Changing styles of individual components, such as adding rounded corners.
These branding settings apply to both the default checkout and any UI extensions you install, ensuring a consistent experience.
Adding new functionality with apps and extensions
Checkout Extensibility makes it easy to install or build apps that add new features. Shopify’s 2024 guide lists examples of tasks you can accomplish without writing code: adding banners, date pickers or gift messages, running loyalty programs, or offering free gifts. Apps can be configured via the checkout and accounts editor and inherit your branding automatically.
Some common use cases include:
Collecting extra information – Add fields for delivery dates, PO Boxes, purchase order numbers or special instructions.
Upsells and cross‑sells – Use post‑purchase apps to surface one‑click upsells or loyalty programs on the Thank you page.
Trust and communication modules – Insert trust badges, FAQ sections or contact modules using checkout extensions.
Integrated services – Display dynamic shipping insurance quotes or real‑time financing offers through widgets integrated with third‑party services.
For more advanced requirements, you can build custom apps using the Shopify CLI and UI extension APIs. Shopify’s developer docs show how to scaffold an extension and configure targets in the shopify.extension.toml file. You can then render React/Preact components within the checkout’s remote DOM.
Leveraging Shopify Functions
Functions are server‑side hooks that extend Shopify’s backend logic. They are the upgrade‑safe replacement for Shopify Scripts. Use cases include:
Custom discounts – Create product‑specific or cart‑wide discounts that stack or combine according to business rules.
Shipping and payment rules – Sort or rename shipping methods, exclude PO Box addresses, or limit payment methods based on cart contents.
Cart and checkout validations – Validate orders against complex conditions (e.g., minimum order value for B2B buyers).
Functions run within Shopify’s infrastructure, so they scale automatically and remain compatible with future updates. If you’re migrating from Shopify Scripts, note that Scripts will be deprecated by June 2026. Use this time to rewrite your logic as Functions or install apps that implement similar functionality.
Best practices for migrating to Shopify Checkout Extensibility
Migrating from checkout.liquid requires planning. Here are steps to ensure a smooth transition:
Audit existing customizations – Identify scripts, upsells and analytics embedded in your current checkout. Shopify provides a personalized upgrade guide for Plus merchants.
Review installed apps – Upgrade apps that already support Checkout Extensibility and replace incompatible apps with alternatives.
Replace script-based customizations – Recreate custom code using blocks, web pixels and Functions; note that the Additional Scripts area became read‑only on August 28 2025.
Test using Checkout Dev Preview – Rootsyntax recommends testing extensions in Shopify’s dev preview to simulate the live environment.
Plan for versioning and updates – Create a versioning strategy because API changes or new features can affect your extension’s behaviour.
Monitor performance and analytics – Use app pixels or custom pixels to track conversions and adjust your checkout based on data.
When to use Shopify Checkout Extensibility vs. checkout.liquid
The Rootsyntax comparison table shows that Checkout Extensibility works on all Shopify plans (with some limitations), while checkout.liquid is Plus‑only. Extensibility is modular, secure and compatible with Shop Pay and future upgrades. In contrast, editing checkout.liquid exposes you to maintenance burden, security risks and broken functionality when Shopify releases updates. Unless you need a feature that isn’t yet available in the new framework, migrating now will protect your store against forced upgrades and lost customizations.
Conclusion: Embrace a future‑proof checkout
Shopify is rapidly evolving its checkout to support one‑page flows, buy‑it‑now buttons and other innovations. Shopify Checkout Extensibility ensures that merchants can keep their brand and functionality without hacking theme files. By using extensions, functions and pixels, you can:
Customize branding, insert modules and collect additional information through UI extensions and blocks.
Implement complex discount, shipping and payment logic with Functions.
Track behaviour and manage analytics using pixels.
Migrating from checkout.liquid may require some work, but it will pay dividends in performance, security and access to new features. Start by auditing your current customizations, upgrading compatible apps, and experimenting with the checkout and accounts editor. With Shopify Checkout Extensibility, you can deliver a tailored, high‑converting checkout experience that keeps pace with Shopify’s innovation.
