What is CLS? (What is Cumulative Layout Shift?)

What is CLS? (What is Cumulative Layout Shift?)

Hey there! Have you ever been reading something on a website, maybe looking at a cool new product, and all of a sudden, everything jumps around? You were about to click a button, but then poof! The button moves, and you accidentally click on something else entirely. It’s super frustrating, right? That annoying “jumpiness” has a name in the web world: it’s called Cumulative Layout Shift, or CLS for short. It’s a big deal because it makes websites feel unstable and can really mess up your online experience.

Imagine building a tower with blocks, and just as you’re about to put the top block on, the table shakes, and everything shifts. That’s what CLS feels like for your fingers and eyes when you’re browsing the internet. It’s not just a minor annoyance; it can make a big difference in how much you enjoy a website and even whether you decide to stick around or leave. Let’s dive in and understand this “wobbly website” problem better and see why it matters so much.

What Exactly is CLS? The ‘Wobbly’ Website Problem Explained

Alright, let’s break down CLS into plain English. Cumulative Layout Shift is a way to measure how much a website’s content moves around unexpectedly while it’s loading or while you’re interacting with it. Think of it like a fidgety friend who just can’t sit still. When parts of a web page shift their position without you telling them to, that’s a layout shift.

The “cumulative” part means it adds up all these unexpected movements that happen during your visit. So, if a picture loads, then text pops in above it, pushing everything down, and then an advertisement suddenly appears at the top, pushing everything down again, all those shifts get counted. The more things move, and the bigger the movement, the higher a website’s CLS score will be. And when it comes to CLS, a lower score is always better, because it means your website is more stable and less jumpy.

It’s crucial for websites to feel steady. When a page doesn’t shift, it makes browsing easy and enjoyable. Nobody likes trying to read a paragraph only for it to disappear off-screen because an image decided to load above it. This kind of instability can be incredibly distracting and can even make you abandon a website altogether, especially if you’re trying to complete an important task, like making a purchase or filling out a form.

Why Does CLS Matter So Much? It’s More Than Just Annoying

You might be thinking, “Okay, so things move around a bit. Is it really that big of a deal?” The answer is a resounding yes! CLS isn’t just a small annoyance; it has significant consequences for both people using websites and the businesses that own them. Let’s explore why:

1. Bad User Experience: This is the most obvious one. When a website keeps shifting, it’s incredibly frustrating. It can lead to misclicks, where you try to tap a button but end up hitting something else because the content moved. This can happen when you’re trying to add an item to your cart, click a “Read More” link, or even just scroll through a list of products. A jerky experience makes people less likely to stay on your site.
2. Lower Engagement: If a website is difficult or unpleasant to use, visitors won’t stick around. They’ll spend less time on pages, explore fewer sections, and are less likely to come back. Imagine trying to read interesting customer stories or browse through a loyalty program’s benefits on a site that’s constantly moving – it becomes a chore instead of a pleasant discovery.
3. Hurts Your Business Goals: For online stores, CLS can directly impact sales and other important actions. If customers can’t easily click the “buy” button or struggle to navigate to the checkout, they might give up. This means fewer purchases, fewer sign-ups for newsletters, and a general loss of potential customers. A smooth experience is vital for converting browsers into buyers, which is why things like ecommerce conversion rates are so important.
4. Impacts Search Engine Rankings: Google cares a lot about how people experience websites. They’ve even made CLS a part of their “Core Web Vitals,” which are important signals they use to decide where a website should rank in search results. Websites with good Core Web Vitals, including a low CLS score, tend to rank higher. This means more people can find your site when they search online.
5. Damages Brand Trust: A stable, well-designed website shows that a business cares about its customers’ experience. A jumpy, unpredictable site, on the other hand, can make a business seem unprofessional or untrustworthy. Building trust is essential, especially when asking customers to share personal information or make a purchase.

In short, a high CLS score can chase away visitors, hurt your online visibility, and ultimately cost businesses money. Making sure a website is stable is a foundational step for providing a great customer experience.

How Do Websites Get CLS? Common Culprits

So, what causes all this unwanted movement? It’s usually a mix of different things happening behind the scenes as a website loads. Think of these as common pitfalls that web designers and developers try to avoid. Let’s look at the main reasons why a page might start to wobble:

Images and Videos Without Dimensions

This is one of the most frequent offenders! When a website loads an image or video without telling the browser how tall and wide it is, the browser doesn’t know how much space to reserve. It just shows the text first, and then, *poof*, the image finally loads, pushing all the text down to make room. It’s like trying to fit a puzzle piece without knowing its shape – you only find out when you try to put it in, and everything else has to move.

Ads, Embeds, and Iframes

Advertisements, embedded maps, social media posts, or videos from other sites (like YouTube) are often added to web pages. The problem is, these elements sometimes load much later than the rest of the content. And when they do, they can be a surprise size! If the browser hasn’t reserved enough space for them, they’ll suddenly expand and push everything around. This is especially common with ads that might change size based on who’s viewing them.

Dynamically Injected Content

Sometimes, content appears on a page because of something you did (like clicking a button) or because the website fetched new information. For example, a “Related Products” section might load after the main product description. If this new content isn’t added carefully, and space wasn’t saved for it, it will just barge in and rearrange the existing layout. Think of a pop-up window appearing from nowhere and pushing the main content down – that’s a dynamic injection causing a shift.

Web Fonts Causing FOIT/FOUT

Websites often use special fonts to make them look unique and stylish. But these fonts take a moment to download. While they’re downloading, the browser usually shows a basic font (called a “fallback” font). When the special font finally loads, it might be a different size, causing the text to reflow and shift its position. This is known as Flash of Unstyled Text (FOUT) or Flash of Invisible Text (FOIT), and it’s a common cause of layout shifts.

Actions Waiting for Network Responses

Imagine you have a section on a page that displays personalized recommendations or a customer’s loyalty points. This information often needs to be fetched from a server over the internet. If the website doesn’t reserve space for this content while it waits for the server to respond, then when the data finally arrives, it suddenly appears and pushes other elements around. It’s like waiting for a delivery; if you don’t clear a spot for it, you’ll have to quickly rearrange things when it arrives.

Understanding these common culprits is the first step in making a website more stable and user-friendly. By anticipating where shifts might occur, developers can take steps to prevent them.

Measuring CLS: How Do We Know It’s Happening?

Okay, so we know what CLS is and what causes it. But how do we actually figure out if a website has a CLS problem, and how bad is it? Luckily, there are tools and standards that help us measure this. Google, in particular, has given us clear guidelines and tools.

Google’s Core Web Vitals

Google introduced Core Web Vitals as a set of important metrics that measure the real-world user experience of a website. CLS is one of the three main Core Web Vitals, alongside LCP (Largest Contentful Paint, measuring loading performance) and FID (First Input Delay, measuring interactivity). These metrics are like a report card for how good your website feels to use.

• Good CLS Score: A website is considered to have a “good” CLS score if it’s 0.1 or less. This means very little, or no, unexpected movement.
• Needs Improvement: A score between 0.1 and 0.25 indicates that there’s some layout shift that should be addressed.
• Poor CLS Score: If the score is above 0.25, the website has a significant layout shift problem that needs urgent attention.

Google uses these scores as a factor in its search rankings, so having a good CLS score isn’t just about making users happy; it’s also about helping people find your website more easily.

Tools to Check Your CLS Score

You don’t need to be a coding wizard to check a website’s CLS score. Google provides several free and easy-to-use tools:

• PageSpeed Insights: This is probably the most popular tool. You just type in a website’s address, and it gives you a detailed report, including its CLS score and suggestions for improvement. It checks both mobile and desktop performance.
• Google Search Console (Core Web Vitals Report): If you own a website, Search Console gives you a report on your site’s overall Core Web Vitals performance across many pages. It helps you identify pages that need the most help.
• Lighthouse: This tool is built right into your web browser (like Chrome). You can open the “Developer Tools” (usually by pressing F12 or right-clicking and selecting “Inspect”), go to the “Lighthouse” tab, and run an audit. It will give you a CLS score and many other performance insights.
• Web Vitals Browser Extension: For a quick check while browsing any site, you can install the Web Vitals browser extension. It shows you the Core Web Vitals scores in real-time right in your browser toolbar.

Using these tools regularly helps website owners keep an eye on their CLS and ensure their visitors have a smooth, enjoyable experience. Staying on top of these metrics helps to improve the overall customer experience.

Fixing CLS: Making Your Website Stable and Happy

The good news is that most CLS issues can be fixed with some careful planning and coding. It’s all about making sure the browser knows exactly how much space each part of your website needs before it even starts showing things. Let’s look at some effective strategies to banish those frustrating layout shifts.

Always Set Image and Video Dimensions

This is the golden rule! For every image and video on your website, tell the browser its width and height attributes in the HTML. Even better, you can use modern CSS techniques like aspect-ratio to reserve the correct amount of space. This way, when the browser loads the page, it instantly knows how big the picture or video will be, and it won’t have to push things around when the actual media file finally arrives. This simple step prevents a huge number of common shifts.

Be Smart with Ads and Embedded Content

• Reserve Space: Just like with images, always try to reserve space for ads or embedded content before they load. If you know an ad slot will be 300 pixels wide and 250 pixels tall, create an empty container with those dimensions.
• Place at the Bottom: If possible, consider placing dynamic content like ads or embeds lower down on the page, or in areas where a shift won’t disrupt the main content you’re trying to show. Content below the fold (the part you have to scroll to see) causes less noticeable CLS.
• Avoid Inserting Above Existing Content: Never insert an ad or embedded widget directly into existing content, pushing it down. Find a designated, stable spot for it.

Handle Dynamic Content Carefully

For content that appears after the page loads (like notifications, related products, or social feeds), it’s important to:

• Reserve Space: Again, the theme is reserving space. If you know a customer review widget is going to load, create a placeholder for it with estimated dimensions. This prevents sudden jumps.
• Use Placeholders: Display a placeholder or a simple loading animation in the area where new content will appear. This occupies the space and gives a visual cue to the user without causing a shift.
• Trigger on User Interaction: If content appears only after a user clicks something (like an “Expand” button), that’s generally fine, as the user expects a change. The problem arises with unexpected changes.

Platforms like Yotpo Reviews are designed to integrate smoothly, ensuring that customer product reviews and other user-generated content appear without causing jarring shifts, contributing to a stable and pleasant shopping experience. This is crucial for showcasing authentic content like User-Generated Content (UGC) effectively.

Preload Fonts and Use font-display

To prevent text from shifting when custom fonts load:

• Preload Important Fonts: Use <link rel="preload"> in your HTML to tell the browser to download important fonts early, so they’re ready when the page needs them.
• Use font-display: swap;: In your CSS, use font-display: swap; for your custom fonts. This tells the browser to use a basic fallback font immediately, and then swap it for your custom font once it’s loaded. This still causes a small shift, but it’s often preferred over a blank space (FOIT) and provides a better user experience than a completely unmanaged shift.

Reserve Space for Future Content

Sometimes, content just takes a while to arrive, perhaps from a database or another service. In these cases, it’s best to reserve the space using a technique called “skeleton screens” or “content placeholders.” These are simple grey boxes or shapes that mimic the layout of the content that will eventually appear. They hold the space until the real content arrives, preventing any layout shifts. This provides a much smoother visual experience for the user.

By implementing these strategies, web developers can create websites that are not only beautiful but also stable and enjoyable to use. A little bit of foresight goes a long way in preventing those irritating content jumps.

CLS and Your Business: Why Stability is Key to Success

Beyond the technical jargon, what does a low CLS score truly mean for your business? In the competitive world of online commerce, every detail matters. A stable website isn’t just a nicety; it’s a fundamental aspect of a successful digital strategy. Let’s connect the dots between layout stability and your business goals.

Keeping Customers Engaged

Think about your favorite online store. Does it feel smooth and responsive, or does it constantly jump around? A website with low CLS feels professional and reliable. When customers don’t have to worry about misclicking or losing their place, they’re more likely to explore your products, read product descriptions, check out product reviews, and engage with your brand. This increased engagement can lead to longer site visits and a deeper connection with your offerings.

Building Trust and Credibility

In the digital age, trust is paramount. A wobbly website can unconsciously signal a lack of attention to detail, or even imply that the business isn’t very professional. On the flip side, a stable, well-performing website conveys competence and reliability. When customers feel comfortable and confident navigating your site, they’re more likely to trust you with their purchase and their personal information. This trust is invaluable for customer retention and building a loyal customer base, which you can learn more about in resources like this one.

Boosting Conversion Rates

This is where CLS directly impacts your bottom line. Every time a layout shifts unexpectedly, there’s a risk of a misclick or a moment of frustration that leads a customer to abandon their cart or leave your site. A stable experience ensures a clear path to conversion, whether that’s adding an item to a cart, signing up for a newsletter, or completing a purchase. Imagine a customer deciding to make a purchase, and as they go to click “checkout,” the button moves! That frustration can easily turn into a lost sale. Improving your website’s stability contributes directly to a better ecommerce conversion rate.

Improved SEO

As we discussed, Google uses Core Web Vitals, including CLS, as a ranking factor. A better CLS score can mean higher rankings in search results, which translates to more organic traffic to your site. More visitors mean more potential customers, without having to spend extra on advertising. This is free, high-quality traffic driven simply by providing a better experience.

In essence, treating CLS seriously is an investment in your customer experience, brand reputation, and ultimately, your business’s growth. A seamless and stable online environment paves the way for satisfied customers and a thriving business.

How Yotpo Helps with User Experience

At Yotpo, we understand that a fantastic user experience is at the heart of building strong customer relationships and driving business success. While we focus on empowering brands with powerful tools for customer advocacy and engagement, our products are built with performance and stability in mind, ensuring they contribute positively to your website’s overall health and CLS score.

Yotpo Reviews: Stable Widgets for User-Generated Content

Collecting and displaying customer reviews and User-Generated Content (UGC) is incredibly powerful. Yotpo Reviews is designed to integrate seamlessly into your website, providing robust widgets that showcase authentic content like star ratings, written reviews, and customer photos. Our widgets are engineered to load efficiently and reserve appropriate space, minimizing layout shifts. This means that when a customer lands on a product page, they see those valuable reviews without the page jumping around. It’s about presenting compelling social proof in a way that enhances the user experience, rather than detracting from it. By ensuring our review widgets are stable, we help brands maintain a low CLS score, which contributes to higher engagement and trust.

Yotpo Loyalty: Smooth Experiences for Rewarding Customers

Building loyalty programs is a fantastic way to keep customers coming back. Yotpo Loyalty empowers brands to create engaging rewards programs that delight customers. Our loyalty components, whether they are on-site pop-ups for points notifications, or dedicated loyalty program pages, are developed with an emphasis on performance and a smooth user interface. We ensure that these elements are integrated thoughtfully, so they don’t unexpectedly push content around. When customers interact with their loyalty points balance, redeem rewards, or learn about new ways to earn, they experience a consistent and stable interface. This seamless experience is crucial for encouraging participation and making customers feel valued, reinforcing positive interactions with your brand and contributing to a great overall loyalty experience.

By focusing on efficient loading and thoughtful integration, both Yotpo Reviews and Yotpo Loyalty are built to enhance your website’s functionality without negatively impacting critical performance metrics like CLS. We believe that empowering brands with best-in-class solutions means ensuring those solutions are also best-in-class in terms of website stability and user experience.

Summary: Preventing the Wobbles

Let’s quickly recap what we’ve learned about CLS. It stands for Cumulative Layout Shift, and it’s a measure of how much your website content unexpectedly moves around while you’re trying to use it. Think of it as the “wobble factor” of a website. A low CLS score (0.1 or less) means a stable, pleasant experience, while a high score means frustration and potential lost customers.

The main culprits behind these shifts include images and videos without defined sizes, slow-loading ads or embedded content, dynamic content that just pops in, and even special fonts taking time to load. Google cares a lot about CLS as part of its Core Web Vitals because it directly affects how much people enjoy and trust a website. Tools like PageSpeed Insights can help you discover your CLS score.

The good news is that preventing CLS is often about proactive planning: always defining image sizes, reserving space for dynamic content, and smart font loading. Doing so not only makes your visitors happier but also helps your business grow by improving engagement, building trust, boosting conversion rates, and even helping your website show up higher in search results.

Ultimately, a stable website is a happy website, both for those visiting it and for the businesses running it. By making sure your digital storefront is steady and predictable, you create a welcoming environment that encourages customers to explore, connect, and come back again and again.

A Stable Website is a Happy Website

Making sure your website stays steady and doesn’t jump around is one of the best things you can do for your online business. It’s like having a smoothly paved road instead of a bumpy one – everyone prefers the smooth ride! When you provide a predictable and delightful experience, customers are more likely to explore your products, read those glowing reviews, and participate in your awesome loyalty program. They’ll feel comfortable and confident, which means they’re more likely to make a purchase and stick around to become your most devoted customers.

Focusing on a low CLS score shows you care about every detail of your customer’s journey. It’s a key ingredient in building trust and turning casual browsers into loyal fans who rave about your brand. Keep your website steady, and you’ll keep your customers happy!