The Big Cut Is Here—Why Shopify Functions Are Now the Reality at Checkout

As a Shopify Plus user, you're probably familiar with the old Shopify Scripts.

The entire Shopify functionality in the checkout process has now undergone a definitive transformation. Since the hard sunset of Shopify Scripts on June 30, 2026, the old environment no longer works. Shopify Functions is now the only option for complex customizations at checkout. As the official successor to Shopify Scripts, it resolves long-standing latency issues. For Shopify merchants, this means that anyone who hasn’t yet migrated their checkout logic needs to act quickly.

We will show you in this article what Shopify Functions is, how it works and how your business can benefit from it.

What is Shopify Functions?

Shopify Functions enables developers to customize backend logic and create custom functions for a Shopify store. With Shopify Functions, all Shopify merchants can now extend existing Shopify functions and tailor them to their business needs.

Moreover, functions can be configured directly in the admin area without touching a line of code. This is possible because these functions are installed with an app. Even though Functions only offers the familiar changes for discounts, shipping, and payment methods, Shopify has announced plans to add features for shipping rates, checkout and shopping cart validations, returns validations, and order routing in the coming time.

Why Shopify Scripts Was Replaced by Shopify Functions

Shopify Scripts has been replaced by Shopify Functions to provide a flexible, scalable and future-proof solution. While Shopify Scripts was reliant on Ruby-based scripts and therefore a technical barrier to entry, Shopify Functions is based on modern programming languages such as JavaScript, which are more accessible. Shopify Functions enables significantly greater customization, allowing merchants to efficiently implement complex business logic. Shopify Functions also offers better scalability as it can easily handle large amounts of data and requests, making it ideal for growing businesses and multi-store setups. Functions can also be applied across multiple stores, which simplifies administration. Unlike Shopify Scripts, which has seen little long-term development, Shopify Functions receives continuous support and is better suited to the long-term needs of merchants.

The Technical Limitations of the Old Ruby Environment

Shopify Scripts was based on the Ruby programming language and ran in an isolated sandbox environment. This created a high technical barrier to entry and occasionally led to performance bottlenecks when dealing with very large amounts of data. The old environment simply could no longer keep up with the growing demands of large multi-store setups.

The hard sunset on June 30, 2026: What happens if you missed the migration?

The final technical shutdown took place on June 30, 2026. If you missed the transition, your old checkout rules, shipping logic, and discount promotions will no longer apply. This can lead to abandoned purchases and massive revenue loss. In this case, immediate migration by technical experts is absolutely essential.

How Shopify Functions works

In summary, Shopify Functions allows developers to create serverless functions using common programming languages such as JavaScript, TypeScript, and Rust; to do so, the code must be compiled in WebAssembly. The functions can then be uploaded to Shopify infrastructure, where they are executed in response to events, such as a new order or customer data update.

You can use the Shopify API to interact with your Shopify store and perform various tasks. With this Shopify API, you can access the store's data and functions to easily create custom solutions based on Shopify.

The innovative Functions architecture provides open-source flexibility without the need for hosting, security, or forked code management. Because Functions are hosted on the Shopify infrastructure, they are always up to date and able to handle all the important tasks, even for larger Flash sales.

The Architecture: Why WebAssembly (WASM) Is the New Standard

At the heart of this new technology is Shopify Functions WASM (WebAssembly). Every Shopify Functions tutorial for developers today begins with an understanding of this WASM architecture, as it forms the foundation for its extreme speed.

What was Shopify Scripts?

Shopify Scripts is a feature that allows Shopify Plus merchants to extend and customize their stores by adding custom scripts, such as to customize the checkout process. However, support for Shopify Scripts was discontinued on August 13, 2024.

Since the final deadline expired on June 30, 2026, all legacy Ruby scripts are now permanently inactive. Merchants who have not yet migrated to Shopify Functions will consequently lose critical checkout logic and discount promotions. An immediate migration to the new WebAssembly-based Functions architecture is now absolutely necessary to prevent abandoned carts and restore the online store’s full functionality.

Shopify Functions advantages

1. Improved performance

Shopify Functions are built on AWS Lambda, a serverless computing platform. This allows Functions to automatically scale up or down depending on the number of requests. This ensures that a store remains responsive even in times of high traffic. This can reduce page load times and improve the overall user experience.

2. Increased security

To protect against potential security vulnerabilities, Shopify Functions runs in a secure environment provided by AWS Lambda. It is also possible to configure Shopify Functions to only access the specific data and resources they need to operate - further reducing the risk of unauthorized access.

3. Flexibility

The new Shopify Functions technology gives developers and store operators a high degree of flexibility. Thanks to the ability to create custom functions and workflows, companies can adapt their store to specific needs and customer requirements.

4. Checkout customizations without external apps

With Shopify Functions, merchants can now make checkout customizations directly in Shopify without external apps, which in many cases was previously only possible via apps or Shopify scripts. Shopify Functions offers more flexibility and advanced customization options that allow for even more precise control of checkout logic.

5. Maximum Performance on the Shopify Edge Instead of Server Latency

Since Functions run directly on Shopify’s global edge infrastructure (on AWS Lambda), the system scales automatically. Billions of requests can be processed, and according to Shopify itself, execution latency is less than 5 milliseconds. For customers, this means no noticeable loading times at checkout.

6. Security and Checkout Customizations Without App Proliferation

In the past, countless external apps had to be installed for many small customizations, which negatively impacted page load times. Today, Shopify Checkout Functions can be controlled directly through the backend. Running them in a secure environment also drastically minimizes the risk of unauthorized access.

What is possible with Shopify Functions

Scalable performance and faster execution

Shopify Functions is designed to support even the largest organizations by handling billions of requests. Thanks to improved architecture, execution latency has been reduced by up to 57%, resulting in significantly faster processing. In addition, the latency of parallel function APIs has been reduced by 50%.

Extended customization options for the checkout

Shopify Functions can be used to create custom validation logic for the shopping cart and checkout. Merchants can reserve items for specific customer groups, define mandatory fields or set specific purchase criteria. Checkout customizations are now also available for draft orders to ensure a consistent shopping experience.

Flexible discount functions

The discount functions enable even more granular pricing:

• Multiple discounts in a single function: retailers can implement volume discounts, tiered promotions and multiple impact discounts.

• Customizable discount logic: The new “discount distributor” feature allows you to control which discounts are prioritized.

• Advanced shipping discounts: Merchants can apply discounts based on shipping options, shopper identity or purchase history.

Development and debugging tools

Shopify Functions offers advanced development and debugging features:

• Log streaming and replay: Functions logs can now be analyzed directly in the Shopify CLI.

• Shared Functions logs: Merchants can share logs to better monitor successful and failed flows.

• Increased input limit: The input size has been doubled to 128 KB to avoid scaling issues.

Modernized development environment

Shopify Functions supports the latest libraries in Rust and soon also in JavaScript. This reduces the code footprint and the functions run up to 40% faster.

Improved integration into the theme

Customizable buttons for accelerated checkout: These can be adapted to the respective store design.

Support for Shopify Functions and Bundles on shopping cart and product pages: Expands the possibilities for product presentation and design.

Who is Shopify Functions suitable for?

First and foremost, Shopify Functions was introduced for developers and businesses who want to extend the functionality of their Shopify store. However, it is also suitable for businesses that need to automate their routine tasks or integrate with other systems or services.

We'll show you some examples of who Shopify Functions is suitable for below:

1. Small businesses

Shopify Functions can be especially beneficial for small businesses with limited resources. By automating routine tasks (such as updating inventory), businesses can save time and reduce the risk of errors.

2. Medium to large businesses

Shopify Functions is also useful for medium to large businesses. For example, businesses can use a custom function to integrate with their own inventory management system or automate the printing of shipping labels to enable efficient shipping options.

3. Companies with complex requirements

For complex requirements that can't be met by off-the-shelf solutions, Shopify Functions offers a high degree of flexibility to implement these business needs.

4. Developers

Shopify Functions is also naturally an ideal platform for developers to create custom functions for their customers' Shopify stores. Developers can create scalable, powerful applications that integrate seamlessly with Shopify.

Why should merchants use Shopify Functions?

Shopify merchants can maximize the potential of Shopify Functions to improve their business in a number of ways.

With Shopify's new feature, merchants can customize their shopping cart and checkout processes to optimize conversions and provide customers with a seamless shopping experience.

Merchants can thus create dynamic discounts based on factors such as order value or customer location. In addition, merchants can use Shopify Functions to integrate additional payment options so customers can choose the method they prefer and more.

With an effective use of Shopify Functions, it is possible for merchants to improve their overall management and gain valuable insights from detailed reports on sales and performance. Shopify Functions thus provides you with a flexible and powerful toolset to achieve the business needs you require.

Shopify Functions examples: These are the Shopify Functions API

• Product Discount API: Create an innovative discount form that is applied to a specific product or product variant in the shopping cart.

• Order Discount API: Develop an innovative discount type that is applied to all items in the shopping cart.

• Delivery Customization API: Name, structure and rearrange the delivery options available during the checkout process.

• Payment Customization API: Rename, structure and rearrange the payment methods available during the checkout process.

• Cart and Checkout Validation API: Implement your own validation for the cart and checkout process.

• Order Routing Location Rule API: Assign a customized order routing location sequence for each item when routing the order.

• Fulfillment Constraints API: Define your own logic for how Shopify should fulfill and assign an order.

• Shipping Discount API: Develop an innovative discount variation that is applied to one or more shipping rates during checkout.

• Cart Transform API: Expand items in the cart and update how cart items are displayed.

Conclusion

Shopify Functions offers developers many ways to create custom components for their website. This allows merchants to tailor their website to the needs of their customers and provide a personalized shopping experience.

The Toolset is already available to everyone and offers all the features that Scripts provides. As a Shopify Plus agency, we, too, will be relying on Shopify’s new feature going forward, following the phase-out of Shopify Scripts on August 13, 2024, and its final discontinuation on June 30, 2026.