Never update the live theme directly. Duplicate it, apply the update to the copy, test the pages that make you money, and only then publish. Keep the old version around as a rollback. The whole process takes under an hour and prevents the most common way stores break themselves.
Theme updates change code you may have customized. If a developer edited your theme's Liquid templates, added custom JavaScript, or adjusted CSS, the update can overwrite those edits or conflict with them. App embeds and app blocks usually survive updates, but older apps that injected code directly into theme files often do not. The result is a store that looks fine on the homepage but has a broken product page, a dead checkout button, or a layout shift that tanks mobile conversion. None of this is visible until a customer hits it.
In the theme editor, duplicate your current live theme and name the copy with the date and version, something like "Live 2026-09-25 before v14.2 update." This copy is your rollback. If anything goes wrong later, you can publish this duplicate in seconds and be back to exactly where you started. Do not skip this because the update "looks small." Small updates break custom code too.
Apply the theme update to the duplicated copy, not the live theme. Shopify will either update the duplicate in place or create an updated version you can customize. If the theme offers a "customize with your settings copied over" option, use it, but verify afterward that the settings actually carried over. Sections, colors, and fonts usually transfer; custom code in theme files does not, and that is where the testing begins.
List every customization in the old theme: edited templates, custom Liquid sections, added scripts, CSS changes. Then check each one in the updated copy. The fastest method is to compare the code files side by side and reapply your edits to the new version. If you do not know what was customized, check with whoever built the store before updating, or look for the telltale signs: code comments with a developer's initials, snippets with custom names, or script tags pointing at custom files.
Preview the updated theme and walk the critical paths on both desktop and mobile: homepage, collection page, product page with variant selection, cart, and checkout. Add a product, apply a discount code, and go as far into checkout as you can without paying. Check that apps render where they should: reviews under the buy button, upsells in the cart, chat widgets in the corner. Test on a real phone, not just a resized browser window, because tap targets and layout shifts behave differently on touch devices.
Run the updated theme's key pages through a speed test and compare against the live theme's numbers. Updates sometimes add JavaScript or heavier sections that slow things down. Watch Largest Contentful Paint and Cumulative Layout Shift specifically: a theme update that shifts the product page layout on load will cost conversions even if everything "works." If the new version is meaningfully slower, find out why before publishing; it is often one new section or script you can remove or defer.
When the duplicate passes every test, publish it. Keep the old live theme (now a backup) unpublished for at least two weeks. Watch your analytics for the first few days: conversion rate, bounce rate on the product page, and any spike in support messages about the site looking broken. If something slipped through testing, you can roll back to the backup in one click while you fix the new version. A calm update process beats a fast one every time.
Source: web.dev, Largest Contentful Paint (LCP); web.dev, Cumulative Layout Shift (CLS). Reviewed Sep 25, 2026.
Test misspellings, plural forms, product types, and attribute searches like a color plus a category. Search should rank the product a shopper means ahead of blog posts and pages, and it should stay fast with filters active on a real catalog.
Large catalogs, heavy filter scripts, and unoptimized predictive search results are the usual causes. Test search on the biggest collection, on mobile, and on a mid range phone rather than a fast desktop connection.
Apps can improve ranking and filtering, but they add scripts and cost. Start by checking whether the theme search is configured correctly and whether product data is clean, because apps built on messy titles and tags inherit the mess.