Shopify Checkout Extensions Explained: Upsells, Badges & More
Checkout is the most valuable page in your store and, for years, the hardest to change. Checkout UI extensions are Shopify's answer: app-built blocks that slot into checkout and the pages after it. Here is what they can do and how to get one built.
What a checkout UI extension is
A checkout UI extension is a block, delivered by an app, that Shopify renders inside checkout. It is built from Shopify's own UI components, so it inherits your checkout's branding and stays fast and secure, and you place it in the checkout editor the same way you place a theme block.
Extensions replace the old approach of editing checkout templates directly. Shopify has been moving every store onto this model, called checkout extensibility, alongside Shopify Functions for logic such as discounts.
Where they can appear
There are two groups of placements, and the difference matters because of plans:
- Inside checkout — the information, shipping and payment steps. Extensions here are available to stores on Shopify Plus.
- After checkout — the thank-you page and the order status page. Extensions here are available on all plans.
So if you are not on Plus, the thank-you and order status pages are where a checkout extension can work for you. Shopify's plan rules change from time to time, so check the current checkout extensibility documentation for your plan before you build.
The checkout blocks merchants build most
- Post-purchase upsells on the thank-you page — a complementary product offered while intent is highest.
- Trust and reassurance — returns policy, delivery promise, secure-payment badges.
- Delivery notes and gift messages collected and saved to the order.
- Order status helpers — care instructions, setup guides or a support link matched to what was bought.
- Surveys — a one-question “how did you hear about us?” on the thank-you page.
- Loyalty prompts — points earned on this order, or a nudge to create an account.
How to build one without a developer
In AppFly, pick A checkout block from the dropdown under the prompt box — or just say “on the thank-you page” — and describe it:
“A block on the thank-you page that shows a care guide for the product category the customer just bought, with a link to our support page.”
The coding agent writes the extension with Shopify's checkout components, registers it, and installs it on your store. You then place it in the checkout editor, preview it with a test order and iterate in chat. The step-by-step version is in how to build a Shopify app without coding.
Rules worth knowing before you start
- Extensions run in a sandbox. They cannot inject arbitrary scripts or restyle checkout freely; they use Shopify's components. That is what keeps checkout fast and safe.
- Keep them light. One clear message beats three competing ones at the moment someone is paying.
- Logic belongs in Functions. If what you want is a price change — a discount, a shipping rule — that is a discount function or another Shopify Function rather than a UI block. AppFly builds discount rules too.
Frequently asked questions
Can I customise Shopify checkout without Shopify Plus?
Yes, on the thank-you and order status pages, where checkout UI extensions are available on all plans. Extensions inside the information, shipping and payment steps are a Shopify Plus feature.
What is the difference between a checkout UI extension and a Shopify Function?
A checkout UI extension adds something the customer sees, such as a block of content or a form field. A Shopify Function changes logic Shopify runs, such as how a discount is calculated.
How do I add an upsell to the Shopify thank-you page?
Use an app that provides a thank-you page checkout UI extension, then place the block in the checkout editor. With AppFly you can describe the upsell and have the extension built for your store.