Checkout UI Extensions: Replace Script Tags With Polaris Targets

If your store still depends on checkout script tags or a forked checkout.liquid, you are on borrowed time. Shopify's supported path is Checkout UI extensions: custom UI and logic at defined steps, rendered with Polaris web components so the experience matches native checkout.

What you can add

Extensions can show personalized messages during cart review, surface custom payment context, or drop a survey on the thank-you page. You pick a target (where it mounts), use the target API (cart, buyer, shipping), and render Shopify's web components — not arbitrary HTML/CSS that breaks PCI and performance.

Plus vs non-Plus

Shopify is explicit: Checkout UI extensions for the information, shipping, and payment steps are available only on Shopify Plus. Thank-you and order-status customizations have a wider surface. We scope Plus brands to in-checkout upsells and B2B fields; non-Plus brands get post-purchase and account work instead of promising a custom checkout they cannot install.

How we scaffold

cd my-app
shopify app generate extension --template checkout_ui

CLI creates the TOML config plus a Checkout.jsx template. From there we wire targets, keep logic inside the sandbox, and test in a Plus development store. No theme file edits. Uninstalls leave no ghost Liquid.

Source: Checkout UI extensions (2026-07).