How to find what slows down your Shopify store

No single tool answers every question about a slow ecommerce store. Real-shopper data tells you whether people are waiting. A lab test tells you what on the page is slow. ShopWeight tells you which of your apps adds the most processing time.

Most stores get the clearest answer by using the tools in that order. Where you start depends on how much traffic your store gets. Where a step needs a developer, the guide says so.

Start with what real shoppers experience

Shopify's web performance report, in your Shopify admin, shows how fast your store loads for real visitors. It covers the last 90 days and the three Core Web Vitals: loading (LCP), response to taps and clicks (INP) and layout shift (CLS).

The report marks events such as app installs on its timeline. It doesn't say which app caused a change.

Google Search Console's Core Web Vitals report uses Google's Chrome UX Report, which is built from real Chrome users' visits over the past 28 days. Google rates a page as good when all three figures meet their targets for at least 75% of visits. The targets are the main content showing within 2.5 seconds, a response to taps within 200 ms and a layout shift score of 0.1 or less.

Smaller stores may not get enough visits for Google to publish these figures. In that case, start with a lab test.

Find what is slow on the page

PageSpeed Insights runs Google's Lighthouse test on one page, with the settings of a mid-range phone on a slowed mobile connection. It lists the outside scripts on the page by company under "3rd parties."

Each test is a single page load. The score can move by several points from one test to the next.

WebPageTest is another free lab test, with more settings once you create a free account.

Find which apps add the most processing time

Lab tests name companies and web addresses. A Shopify store's scripts come from the apps you installed, from your theme and from Shopify itself. The web address alone doesn't always say which is which.

ShopWeight loads your homepage five times with Lighthouse and matches each script it can identify to the app that loaded it. Each app gets a band, from light to very heavy. For apps measured on at least 20 stores, the report also compares your result with the same app on other Shopify stores.

ShopWeight is free and installs nothing on your store.

If your team already pays for speed monitoring, ShopWeight gives you a quick independent check. Before you install an app, you can check a store that already runs it or look the app up in the App Weight Index.

Check your theme code

Some slowness comes from the theme itself, before any app script runs. Shopify's Theme Inspector for Chrome shows how long each part of your theme takes to render on Shopify's servers. Liquid is the template language Shopify themes are written in. The inspector is built for developers and times each part of that code.

Decide what to do with a heavy app

A heavy app isn't automatically a problem. Weigh its processing time against what it brings in: sales from reviews, email sign-ups, recovered carts.

The usual choices are to keep it, delay it, replace it with a lighter app or remove it. Delaying an app means your developer loads its script after the page appears. Not every app still works when delayed.

When you remove an app, check that its code left your theme too. Some apps add code to your theme files. Uninstalling the app doesn't always remove that code.

Shopify requires apps in its App Store to lower a store's Lighthouse performance score by no more than 10 points. Several apps that each meet that rule can still add up to a slow store.

Check again after a change

Real-shopper figures take time to catch up. Google's figures cover the last 28 days. A change shows in full about four weeks later.

A ShopWeight check shows the difference the same day. Check again from your report page to see which apps changed.

Limits to keep in mind

Lab tests, ShopWeight included, test one page under fixed conditions. Real shoppers use many different phones and connections. They also visit more pages than your homepage.

A few stores skip some scripts when a browser says it is being run by a program. ShopWeight's test browser doesn't say that. On those stores, ShopWeight usually sees the same scripts a shopper's browser gets.

ShopWeight counts only scripts it can match to an app. Scripts it can't match stay out of every app's result.

Common questions

Which apps slow down a Shopify store the most?

It depends on the store and on how each app is set up. The App Weight Index covers apps found on at least 20 of the Shopify stores we've checked. For each one, it shows how often the app landed in each band. A ShopWeight check shows the answer for your own store.

Why does my PageSpeed score change every time I test?

Each PageSpeed Insights test is one load of one page. Page loads vary with the network, the server and the scripts that run. Running several tests and looking at the middle result gives a steadier picture.

Will removing an app speed up my store?

Removing an app usually removes its processing time from the page. Check that uninstalling also removed the app's code from your theme files. A ShopWeight check afterward shows whether the app's scripts are gone.

Is ShopWeight worth using if I already pay for speed tools?

It can be. ShopWeight is a free independent check of your homepage. It names each app it can match and compares it with the same app on other stores when there's enough data. Paid monitoring shows when your speed changes. A ShopWeight check shows which apps add the most processing time.

Check which apps slow your store

Enter your Shopify store's address to see its apps ranked by processing time. It's free and takes a few minutes.

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