Checkout Extensibility on Shopify: Extensions and Developer Limits

What is Checkout Extensibility?

Shopify separates checkout customization into extensions and APIs defined by the platform instead of allowing arbitrary page modifications. For a developer, this means working within documented targets, components and permissions, with an app distributing the extension.

Current documentation is available in Shopify.dev's Checkout technologies.

Which extensions can I use on Basic, Shopify and Advanced?

Several technologies are available on the plans I support, including web pixels, post-purchase extensions, UI extensions for thank-you and order-status pages, customer-account extensions and public apps that use Shopify Functions, according to Shopify’s documented availability.

UI extensions that insert components directly into the information, shipping and payment pages of checkout are not available on Basic, Shopify and Advanced. When a request concerns those areas, I do not promise a change the plan does not allow: I check whether the requirement can be solved elsewhere in the flow or with a supported function.

Thank-you and Order status pages

Post-purchase pages provide useful targets for displaying information and functions compatible with the order context. Even here, an extension must use the data and APIs exposed by Shopify rather than assuming full access to checkout HTML.

Customer Account UI Extensions

Customer-account extensions let apps add functionality to supported account surfaces. They are useful when the function genuinely belongs to the post-purchase relationship, such as information, actions or data customers should be able to access after an order.

Post-purchase extensions

Post-purchase extensions can add experiences after the initial order completion in supported contexts. Availability, access and requirements may change with platform versions, so I always check current documentation before including them in a project.

Web pixels

Web pixels are the official layer for collecting customer events in supported cases, rather than treating checkout as a normal theme page. They are a tracking tool, not a guarantee that every advertising platform will receive or attribute every conversion identically.

Checkout Extensibility and Shopify Functions

The two technologies can operate at different layers. UI Extensions handle interfaces in available targets; Shopify Functions extend some backend logic exposed by the platform. On Basic, Shopify and Advanced, public Shopify App Store apps that include Functions can be used, but the availability of each individual API must be verified.

When is a Shopify app needed?

If a feature must live in a checkout target, customer account or extensible backend logic, the Liquid theme is often not the correct layer. In these cases I design the solution as a Shopify app, separating configuration, logic and extensions from the theme.

My process is:

1. define the actual requirement;
2. identify the correct Shopify surface;
3. verify availability for the merchant’s plan;
4. choose a UI extension, Function, web pixel, API or alternative solution;
5. develop and test errors and edge cases;
6. verify behavior in the real checkout or account surface allowed by the platform.

What I do not promise

I do not treat Checkout Extensibility as a way to make any checkout completely custom. Extensions operate within Shopify’s security and API limits. I also do not promise an automatic conversion-rate increase: a feature can improve a process, but its commercial effect must be measured on the store.

Who develops these solutions?

I am Francesco Guiducci, a freelance Shopify expert and Shopify app developer. Within my scope on Basic, Shopify and Advanced I develop and integrate the features actually available, declaring any plan or API limitation before development.

For app projects see IFG Development.

Updated September 3, 2026 based on current Shopify documentation for Checkout Extensibility.