Shopify speed: the apps are usually the problem

When a Shopify store slows down, the theme usually gets the blame. Shopify's developer docs point somewhere else first: they call auditing and removing unused apps, tracking pixels and third-party scripts the highest-impact fix for responsiveness and overall performance. Each app installed to solve one problem adds a little more code to the storefront, and the cost builds up over months. So we audit apps before we touch anything else.

Why do apps slow a Shopify store down?

Because many of them load JavaScript and CSS on every page, whether that page needs it or not. Every script competes for the browser's main thread, which also handles layout and painting, so heavy scripts delay the page appearing and make taps feel slow. Shopify's docs name the usual suspects:

• Chat widgets that load a large script on every page, even when chat is rarely used.
• Review apps that load everywhere, although reviews only appear on product pages.
• Email capture pop-ups that load on every page, even when set to show on a few.
• A/B testing tools that add blocking JavaScript for every visitor.
• Two analytics or tracking tools measuring the same thing.

Many apps also add script tags without async or defer. The browser then can't show the page until each of those scripts has downloaded and run.

Does uninstalling an app remove its code?

Not always. Shopify's help center says uninstalling an app doesn't automatically remove its code from your theme. Apps that edit theme code directly can leave script tags, stylesheet links or Liquid snippets behind, and Shopify notes that this leftover code can cause quality and performance issues. After removing an app, a developer should:

1. Search the theme files for the app's name and script domains, starting with layout/theme.liquid.
2. Check the snippets/ folder for files the app created, and any {% render %} tags that still call them.
3. Open the live page source and search for the app's domain to confirm nothing still loads.

Before you uninstall, check the app's listing or ask its developer whether any extra removal steps are needed.

Which apps load more cleanly?

Apps built with theme app extensions. They don't edit your theme files: Shopify injects their blocks, scripts and styles for them, and when you uninstall one of these apps, its blocks are removed from your theme automatically and entirely. Their files are served from Shopify's CDN, a script shared by several blocks loads only once per page, and app embed blocks can limit scripts to the pages that need them.

When two apps do the same job, ask whether each one uses theme app extensions. It is a good sign, not a guarantee: the app's own script can still be heavy.

How do you find the app costing you most?

Measure before removing anything. Three checks we rely on:

• Shopify's web performance reports, under Analytics > Reports, use real visitor data and mark app installs, theme updates and new code on the charts. A dip right after an install is a strong clue.
• The Lighthouse Treemap shows every script on a page, grouped by origin and sized by bytes.
• Network request blocking in Chrome DevTools lets you block one app's domain, reload and compare.

Test a home page, a collection page and a product page. A script that looks idle on the home page may be doing real work on a product page.

What about images and theme code?

They matter too, and we check them once the apps are sorted. Two Shopify-specific checks:

• Oversized images. Without srcset and sizes, phones download desktop-sized images. Shopify's image_url and image_tag Liquid filters build responsive images with width and height set, and the main image at the top of the page should load eagerly, never lazily.
• Heavy Liquid loops on collection pages. Loops nested across products and variants grow much faster than the catalogue, so a theme that is quick with a small range can slow down as the range grows. A limit on loops that show a fixed number of products also stops the theme fetching more than it displays.

Should you buy a speed optimisation app?

Be wary. Shopify's developer docs warn that some speed services cheat testing tools: they detect tools such as Lighthouse and serve an altered page, or hold scripts back until the visitor interacts, which lab tests rarely do, so scores rise while shoppers see no benefit. Shopify says it has removed most of these apps from the App Store, but the same techniques are still sold as services. Judge any change by the real-visitor reports and by watching the page load, not by a lab score alone.

Where to start

List every installed app, what it does for sales and which pages need it. Remove what nobody can justify, clean out the leftover code, and watch the web performance reports over the following weeks. Our Shopify stores service includes app and script clean-up, or start with a website review.