Core Web Vitals are Google’s way of assessing if pages on a site are a good experience for their visitors, and from that a page can gain a ranking boost. A page has to be good at all Core Web Vitals to be classed as a good page experience.

  • Largest Contentful Paint (LCP) – How long it takes to show the user the main content
  • Cuminative Layout Shift (CLS) – Is the page stable as the user views and scrolls the page
  • First Input Delay (FID) – Does the page respond quicky to user interactions.

At the moment Shopify have the edge over BigCommerce when it comes to getting good Core Web Vitals scores. Let’s try and rectify that.

The HTTP Archive team have set up a Core Web Vitals Technology Report to show how different platforms have performed over time. It shows how Shopify have recently overtaken BigCommerce in the percentage of visitors to their pages having a good page experience. In fact, BigCommerce has started to go the wrong way!

Let’s focus on BigCommerce and the big question – Why it is not always causing good page experiences?

First Input Delay (FID)

FID is the responsiveness to user interactions. This is currently passed by everyone, so not of a concern.

Cumulative Layout Shift (CLS)

If we look at CLS (unexpected movement of elements on the page) for BigCommerce sites we can see a recent desktop improvement, with both mobile and desktop results now above 40% of page views being a good experience. But that still means over half the page views have jumpy content as the pages load or are used.

In the meantime Shopify have been working hard at improving their own CLS scores. They’ve got their pages to now pass CLS almost 60% of the time.

CLS is a hard one to identify and fix as it is dependent on how a user interacts with a page and is typically caused by theme design errors. The Core Web Vitals report powered by our Tag Rocket app can identify which elements on a page are causing the most CLS issues. With this information you can beeline to where the problem is happening and investigate ways to alter the design, so that the shifts stop happening.

Often a fix can be quite simple once you know which elements are causing issues. If a shift is due to an image or widget suddenly pushing content down as it is loaded, you can fix it by pre-sizing the element involved so that it reserves space for itself.

And fixes can often have a dramatic effect on the number of users getting a good experience. Our Core Web Vitals report can give you updates on a daily basis – good for both monitoring fixes and identifying new issues:

Largest Contentful Paint (LCP)

Looking at LCP (how long it takes to show the main content of a page) for BigCommerce sites and we see desktop giving close to 75% of page views a good experience before an abrupt fall in October. Desktop devices tend to perform better than mobiles because they typically are more powerful and have a better internet connection. But mobile is where Google focuses, so again we have only about half the BigCommerce page views passing this metric. (Ignore the desktop glitch in Feb 2021).

While Shopify have caught up and overtaken BigCommerce in the last few years.

While using the Core Web Vitals report generated by Tag Rocket, I discovered some common LCP mistakes. So I decided to write the BigCommerce LCP Quick Fix article that explains how to fix these common mistakes (coming from Cornerstone) and get your pages passing LCP.

I tried to get these fixes “baked” into Cornerstone (issue raised here). The response indicated that they are going to work on performance optimisation and Core Web Vitals next year.


You can see that an ecommerce site can pass the core web vitals if they put some effort into it.

We want to see BigCommerce sky rocket their way to being the ecommerce platform with the best scores in the world (Shopify holds that mantle at the moment). And it can be done. We’ve already helped several stores dramatically increase the number of visitors that get a good page experience.