E-commerceShopify Speed Checklist: Faster Mobile Pages and Checkout (2026)

A slow Shopify store is rarely one big problem. It is usually a pile of small ones: oversized images, code left behind by apps you uninstalled years ago, third-party scripts that block rendering, and a cart that makes shoppers work too hard. This checklist goes through them in the order that usually pays off, on mobile, which Shopify says accounts for the majority of storefront traffic.

It is the same checklist App369 works through in its fixed-price Shopify Speed & Checkout Tune-Up. Every change below can be made on a duplicate theme and checked before you publish it. Shopify allows up to 20 themes per store, so delete an old copy first if you are at the limit.

Step 1: Measure before you change anything

Pick four URLs that matter: the home page, a busy collection, a best-selling product, and the cart. For each one:

• Run PageSpeed Insights on mobile. If Google has enough real-user data for your store, the top of the report shows your Core Web Vitals from the Chrome UX Report. That field data comes from real visits over the previous 28 days; the Lighthouse score below it is a lab test on one simulated load.
• Run Lighthouse three times and keep the median. Single runs vary a lot.
• Write the numbers down. Without a baseline, you can’t tell whether a change helped.

The three Core Web Vitals and their “good” thresholds are below. Google recommends measuring them at the 75th percentile of real page loads, split by mobile and desktop:

Step 2: Images

Image loading has a direct effect on LCP for most storefronts, according to Shopify’s theme performance guide.

• Serve the right size. Use Shopify’s image_url filter with a width, and image_tag with widths and sizes, so a phone downloads a phone-sized image instead of a 4,000-pixel original.
• Load the hero image first. Never lazy-load the main image above the fold, because that delays it. Mark it for early loading, for example {{ image | image_url: width: 1500 | image_tag: loading: 'eager', fetchpriority: 'high' }}, so the browser fetches it early. Use the preload option sparingly, for one or two images only.
• Lazy-load everything below the fold. Product grids, reviews and footer images can wait. Shopify’s image_tag filter already lazy-loads images in sections further down the page, so check that your theme has not overridden this.
• Set width and height. Images without dimensions push content around as they load, which hurts CLS. The image_tag filter adds both attributes for you; check any hand-written <img> tags in the theme.

Step 3: Leftover app code and third-party scripts

Uninstalling a Shopify app doesn’t always remove what it added to your theme. Older apps often pasted snippets into theme.liquid or product templates, and those keep loading after the app is gone. For a step-by-step cleanup, see How to Remove Leftover App Code From a Shopify Theme.

• Search the theme code for the names of apps you no longer use, and remove their snippets on the duplicate theme.
• List every script that loads on the product page (the Network tab in Chrome DevTools shows them). For each one, ask whether it still earns its keep.
• Load chat widgets, review carousels and pop-ups after the page is usable, not before.
• Keep tracking pixels you rely on. Removing one breaks reporting, not just a script.

To list every third-party script your store loads, and see which block rendering, paste your page source into the free Shopify app script checker.

Step 4: Fonts

• Use one or two font families, and only the weights you actually show.
• Prefer fonts from Shopify’s font library, which are served from Shopify’s CDN, or system fonts, which need no download. Shopify advises against loading fonts from external font services.
• Use font-display: swap so text appears immediately in a fallback font. In Liquid, the font_face filter takes it as an option: {{ settings.type_header_font | font_face: font_display: 'swap' }}.

Step 5: Liquid on collection and product pages

Heavy Liquid slows the server’s response before the browser even starts. The usual suspects are loops over every product in a large collection, nested loops over variants and metafields, and the same snippet rendered many times. Shopify’s Theme Inspector for Chrome shows which Liquid takes the longest to render, so you can fix the slowest part first.

Step 6: Layout shift

CLS problems on Shopify usually come from announcement bars, discount banners and app badges that appear after the page loads, and push everything down. Reserve their space in CSS with a min-height, or render them in the theme instead of injecting them with a script.

Step 7: From cart to checkout

Speed doesn’t help if the cart is hard to get through. Check, on a phone:

• Express checkout. Shop Pay, Apple Pay and Google Pay buttons (Shopify’s dynamic checkout buttons) let returning shoppers skip typing. Show them where your theme supports it.
• The cart drawer. It should open quickly, show the total clearly, and let shoppers change quantities without reloading.
• No surprises. Shipping costs and the returns policy should be visible before checkout, not discovered in it.
• App injections. Upsell and gift-wrap apps that add steps or slow the cart are worth testing with and without.

Shopify’s checkout is edited in the checkout and accounts editor, separate from your theme. On plans below Shopify Plus you can change branding such as logo, colors and fonts, but apps that change the information, shipping and payment pages need Plus. The cart and everything before checkout is in your theme, so that is where you have the most control.

Step 8: Measure again, then publish

Run the same four URLs, three times each, on the duplicate theme, and compare with your baseline. Keep a short log of every change, so if something looks wrong after publishing you know exactly what to undo. Lab scores move faster than field data: Core Web Vitals in PageSpeed Insights reflect the last 28 days of real visits, so give them a few weeks.

When to get help

If you’d rather not spend a week in theme code, App369 does this as a fixed-price tune-up for $750, delivered in 5 business days. You get the baseline and after numbers for four page types, the fixes on a duplicate theme you review and publish yourself, a cart-to-checkout review, and a log of every edit. App369 never publishes to your live store or touches payment or customer data. Thinking about leaving Shopify instead? Read Shopify vs custom e-commerce development first.