Why your Shopify store is slow on mobile, and how to fix it

A Shopify store is usually slow on mobile for a small number of reasons: scripts from apps, images that are larger than the screen, video that loads before anyone asks for it, web fonts, popups that load early and marketing tags that each bring their own code. Each one can be checked. Start by measuring what real shoppers get, then fix the largest cause first.

Measure real visits first

Your own phone on office Wi-Fi tells you little. Two numbers are worth more:

• Real-visit data. Zalify Analytics has a page speed report built from your shoppers' actual visits, page by page. Google's own PageSpeed Insights shows real-visit data too, when a page has enough traffic.
• A lab test for the cause. PageSpeed Insights also lists what slowed the page down. Use it to find the cause, not to judge the result.

The targets, each for at least 75% of visits:

Check the product page and the collection page before the home page. Most ad clicks land there.

1. Remove scripts you don't use

Every app that adds a script to the storefront costs time on every page. Go through your installed apps and remove the ones you no longer use. Then check the theme for code left behind by apps you removed in the past: an uninstalled app does not always take its script with it.

2. Size images for the screen

The largest image at the top of the page usually decides LCP. Upload it at the size it is shown, let the theme serve a smaller version to phones, and don't lazy-load the first image. Lazy-load everything below it.

3. Don't load video before it is wanted

An autoplay video in the hero downloads megabytes before the shopper has seen the headline. Show a poster image and load the video when it scrolls into view or is tapped.

4. Limit web fonts

Two font files are usually enough. Each extra weight is another download, and text that waits for a font delays the whole page.

5. Delay popups and chat

A popup or chat widget that loads with the page competes with the content. Load them after the page is usable. In Zalify Popups you set when a popup appears, for example after a delay or on scroll.

6. Count your marketing tags

Each ad platform's browser tag is another script. Sending purchases server-side, as Zalify Pixel does, means the platforms still receive every order when you keep the browser tags to the ones you need.

When the theme is the limit

If the page is still slow after all six, the theme itself may be the cause. Zalify Theme is built to load fast, and a headless store is the option when the speed you need depends on the architecture. Our store build team does both.

A checklist to run today

1. Read real-visit LCP, INP and CLS for your top product page.
2. Remove unused apps and their leftover code.
3. Resize the first image; stop lazy-loading it.
4. Replace hero autoplay video with a poster.
5. Delay popups and chat.
6. Measure again in a week, on real visits.

Sources

• Web Vitals, web.dev
• Largest Contentful Paint, web.dev
• Interaction to Next Paint, web.dev