What is a theme editor app block?
A theme editor app block is a piece of app functionality — such as Looksy’s try-on interface — that you add, position, and remove inside Shopify’s theme editor, with no edits to your theme’s code.
How app blocks fit into a Shopify theme
Modern Shopify themes are built from sections, and sections hold blocks — small movable units like text, images, or buttons. An app block is a block supplied by an installed app rather than by the theme itself, delivered through what Shopify calls a theme app extension. Once the app is installed, its blocks appear in the theme editor’s add-block list alongside the theme’s own blocks, and you place them the same way. Looksy ships as a theme app extension, so its try-on block behaves like any other block in your product template.
Adding and positioning a block in the editor
From Shopify admin, go to Online Store, then Themes, and choose Customize on the theme you want to edit — for try-on that is usually your product template. Inside a section, choose Add block; blocks from installed apps are listed under the app’s name. After adding the block, drag it to sit where it makes sense against the price, buy buttons, and description, then save. The editor shows a live preview as you work, so you can see the placement before anything is published to shoppers. No code files are opened at any point.
Why app blocks replaced pasted theme code
Older Shopify apps often asked merchants to paste snippets into theme files or injected scripts automatically. That approach broke when themes were updated, and leftover code could stay behind after an uninstall. App blocks avoid both problems: the app’s code lives in the extension, not in your theme files, so theme updates do not disturb it and removing the app removes the block. This is why Looksy’s listing can state that there are no theme code edits and that uninstalling is clean — the block only renders while the app is installed.
What this means for installing Looksy
Practically, adding Looksy’s try-on to your store is a theme editor task, not a development task. Install the app, open the editor, add the Looksy block to your product template, position it, and save — the try-on interface then appears on the storefront for that template. If the block does not appear in the add-block list, confirm the app is installed and that you are editing the theme and template you expect — a block saved to an unpublished theme will not show on your live store. For placement specifics, check the tutorial and app documentation linked from Looksy’s App Store listing.
Sources: the public Shopify App Store listing for Looksy. Last checked 27 July 2026.
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