Checkout app extensions

Checkout app extensions make it easy for developers to extend their app code into checkout, and customize many aspects of the checkout experience.

These app extensions make customizations easy to distribute, fast for merchants to install, and upgrade-safe, enabling merchants to continue getting platform benefits as Shopify releases new features.

Today using checkout app extensions, you can:

  • Add new personalized content such as messages or interactive offers to the post-purchase page
  • Personalize the set of checkout options, such as shipping methods or payment methods

Soon you will also be able to:

  • Add new UI to checkout, such as custom content, messages or interactive elements
  • Capture additional information from the buyer in checkout
  • Validate information input by buyers
  • Create custom discounts

There are two types of checkout app extensions available: UI extensions and Scripts.

UI extensions

UI extensions allow you to add new user interface (UI) and functionality to checkout, and are built into apps using extension points, APIs, and UI components provided by Shopify.

Checkout UI extensions code is hosted on Shopify’s CDN for fast delivery. Your extension code is run securely inside of a Web Worker sandbox in the browser.

UI extensions are designed to provide enough flexibility to support a wide variety of customization use cases, while maintaining guardrails to ensure the trust and performance checkout has always been known for.

Post-purchase UI extension point

The first UI extension point to be released to developers is the post-purchase extension, available in public beta. These extensions allow developers and Plus merchants to surface an offer (such as an upsell) or show content to a buyer on a post-purchase page. This page is shown to the buyer right after they have completed their checkout and confirmed an order, but before they arrive at the thank you page.

Other checkout UI extensions

As development continues on checkout extensions, Shopify will release additional UI extension points for checkout, additional APIs, and new checkout components to expand the set of supported use cases.


Scripts let you add custom server-side logic to checkout, and securely change the behavior of payment methods, shipping rates, and checkout line items.

Currently in developer preview, our newest version of scripts lets developers add scripts to apps for ease of management and distribution. Scripts are hosted and executed on Shopify's infrastructure within a WebAssembly sandbox for fast and secure execution.

This new foundation speeds up the development process, improves reliability, and makes your scripts run much faster.

Shipping and payment scripts

The first Scripts APIs available to customize the checkout experiences are payment methods and shipping methods.

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