Shopify Slow on Mobile? 5 Technical Checks to Improve Speed

1. Check images before code

Images are often among the heaviest resources on a product page or homepage. I verify actual dimensions, format, compression, lazy loading and whether the browser is downloading a file much larger than the space in which it is displayed.

I do not compress everything blindly: hero images, product images and editorial content have different needs. The goal is to reduce unnecessary bytes while maintaining quality consistent with the brand.

2. Verify the JavaScript and apps actually loaded

Each app can have a different impact. Some work mainly in the backend, while others load scripts, widgets and listeners in the storefront. For this reason, I do not consider “number of apps” a sufficient metric.

I check which resources execute on the affected pages, which are necessary and which features overlap. If a feature is simple and belongs in the theme, replacing it with Liquid can make sense; if it requires backend logic, APIs or persistent data, an app is often still the correct solution.

3. Reduce main-thread work

A page can appear loaded and still be unresponsive because the browser is executing too much JavaScript. This can affect interaction metrics such as INP and the perceived fluidity of menus, variants, filters and cart.

The work consists of finding the responsible scripts, reducing what is not immediately needed and verifying that the changes do not break commercial functions or required tracking.

4. Check fonts, CSS and critical resources

External fonts, very large stylesheets and resources loaded in a suboptimal order can delay rendering. Before changing anything I distinguish what is needed above the fold from what can load later.

I avoid aggressive mass optimizations: deferring or removing the wrong resource can cause flashes, unstable layouts or broken components.

5. Analyze Liquid and theme structure

Liquid generates the HTML before the page reaches the browser. If a section produces redundant markup, unnecessary loops or loads components that are not needed, the page can become heavier than necessary.

Here I work on sections, snippets and templates while preserving compatibility with the Shopify editor. The goal is to reduce complexity without turning the theme into code that is difficult to update.

Which metrics should you look at?

Core Web Vitals are a useful reference, but I do not turn them into a commercial formula. LCP, INP and CLS describe aspects of the experience; a technical improvement can reduce friction, but it cannot guarantee a predetermined percentage of conversions or sales.

I therefore compare:

• available real-world Core Web Vitals data;
• repeatable lab tests;
• resource weight and count;
• behavior of key interactions;
• commercial metrics, only after verifying that tracking is reliable.

When a performance app is not enough

If the problem comes from a necessary widget, integration or application feature, “removing JavaScript” is not a solution. You need to understand whether the feature can be rewritten, configured better or replaced.

When dedicated software is needed, I can also work as a Shopify app developer, separating application logic from the theme instead of accumulating workarounds in the frontend.

How I work on Shopify speed

I am Francesco Guiducci, a freelance Shopify expert and Shopify app developer. I work on Basic, Shopify and Advanced plans and treat performance as a problem to measure: baseline, change, test and readback.

If you want to understand what is slowing down your store, you can start with a Shopify audit or a 1:1 consultation.

Updated September 3, 2026.