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Why Core Web Vitals In SEO Are So Important - Expert Insights

Understanding the importance of Core Web Vitals is essential for anyone looking to improve their website’s SEO performance. These specific metrics—Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS)—measure critical aspects of user experience. Google prioritises sites that deliver fast, responsive, and visually stable experiences. By focusing on these metrics, you can enhance your site's performance, boost user satisfaction, and ultimately achieve better search rankings. Read on with UpLink SEO company in London to find out the key details.

What are Core Web Vitals?

Definition and Overview

Core Web Vitals are a set of specific factors that Google considers important in a webpage's overall user experience. These metrics measure key aspects of user experience, focusing on loading performance, interactivity, and visual stability. They are essential for providing a smooth and enjoyable experience for users visiting your site.

Key Metrics: LCP, FID, and CLS

The Core Web Vitals consist of three main metrics:

  • Largest Contentful Paint (LCP): Measures loading performance. LCP should occur within 2.5 seconds of when the page first starts loading.

  • First Input Delay (FID): Measures interactivity. Pages should have an FID of less than 100 milliseconds.

  • Cumulative Layout Shift (CLS): Measures visual stability. Pages should maintain a CLS of less than 0.1.

Why Core Web Vitals Matter

Impact on User Experience

Core Web Vitals are designed to improve the user experience on your website. By focusing on loading speed, interactivity, and visual stability, you ensure that visitors have a seamless and pleasant experience. This not only keeps users on your site longer but also encourages them to return, reducing bounce rates and increasing engagement.

Influence on Search Rankings

Google uses Core Web Vitals as a ranking factor in its search algorithm. This means that websites that perform well on these metrics are more likely to rank higher in search results. By optimising your site for Core Web Vitals, you enhance its visibility and reach a broader audience.

Largest Contentful Paint (LCP)

What is LCP?

Largest Contentful Paint (LCP) measures the time it takes for the largest content element on a webpage to become visible within the viewport. This could be an image, video, or large block of text. LCP is a crucial metric as it directly correlates with how quickly users perceive a page to load.

How to Measure LCP

LCP can be measured using tools like Google PageSpeed Insights, Lighthouse, and the Web Vitals Extension. These tools provide detailed insights into your page's LCP and offer suggestions for improvement.

Tips to Improve LCP

To improve LCP, consider the following strategies:

  • Optimise your images by compressing them and using appropriate formats.

  • Remove unnecessary third-party scripts that might slow down your page.

  • Implement lazy loading for offscreen images.

  • Use a Content Delivery Network (CDN) to speed up the delivery of your content.

First Input Delay (FID)

Understanding FID

First Input Delay (FID) measures the time from when a user first interacts with your page (e.g., when they click a link or tap a button) to the time when the browser begins processing that interaction. FID is crucial for ensuring that your page feels responsive to users.

Measuring FID

FID can be measured using field data from tools like Google PageSpeed Insights and the Web Vitals Extension. These tools show how real users experience interactivity on your site.

Reducing FID

To reduce FID, focus on the following:

  • Minimise JavaScript execution time by breaking up long tasks.

  • Optimise your web page's critical rendering path to speed up interactivity.

  • Use a web worker to run scripts off the main thread.

Cumulative Layout Shift (CLS)

What is CLS?

Cumulative Layout Shift (CLS) measures the visual stability of your webpage. It quantifies how often users experience unexpected layout shifts while a page is loading. A low CLS score indicates that your page is visually stable and provides a better user experience.

Measuring CLS

CLS can be measured using tools like Google PageSpeed Insights, Lighthouse, and the Web Vitals Extension. These tools help identify elements causing layout shifts and provide recommendations for reducing them.

Minimising CLS

To minimise CLS, implement these practices:

  • Use size attributes for images and videos to reserve space.

  • Avoid inserting content above existing content except in response to user interactions.

  • Ensure ads and embeds have a reserved space, preventing unexpected shifts.

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Mobile SEO

Core Web Vitals and Mobile SEO

Importance for Mobile Users

Mobile users form a significant portion of web traffic, making it crucial to optimise for mobile SEO. Core Web Vitals are particularly important for mobile users as they often experience slower connections and less processing power compared to desktop users. A mobile-optimised website ensures a smooth and efficient experience, reducing frustration and keeping users engaged.

Optimising for Mobile Devices

To optimise Core Web Vitals for mobile devices:

  • Implement responsive web design to ensure your site adjusts seamlessly to different screen sizes.

  • Compress images and other media to reduce load times.

  • Use mobile-friendly layouts that prevent layout shifts and improve interactivity.

  • Test your site on various mobile devices to ensure consistent performance and user experience.

Tools for Measuring Core Web Vitals

Google PageSpeed Insights

Google PageSpeed Insights is a powerful tool for measuring Core Web Vitals. It provides a comprehensive analysis of your site's performance, including detailed metrics on LCP, FID, and CLS. The tool also offers actionable recommendations to improve these metrics.


Lighthouse is an open-source, automated tool for improving the quality of web pages. It includes audits for performance, accessibility, progressive web apps, SEO, and more. Lighthouse is integrated into the Chrome DevTools, making it easily accessible for developers.

Web Vitals Extension

The Web Vitals Extension is a Chrome extension that provides real-time feedback on your site's Core Web Vitals. It is a handy tool for developers to monitor performance metrics and make quick adjustments to improve user experience.

Common Issues and Fixes

Slow Server Response Times

Slow server response times can significantly impact LCP and overall page performance. To fix this:

  • Upgrade to a faster hosting provider.

  • Optimise your server configurations.

  • Implement caching strategies to reduce load times.

Render-Blocking Resources

Render-blocking resources, such as JavaScript and CSS files, can delay the loading of your page's main content. To address this issue:

  • Minimise the use of render-blocking resources.

  • Use asynchronous loading for JavaScript files.

  • Inline critical CSS to ensure essential styles are loaded first.

Large Page Size

Large page sizes can slow down your site and negatively impact Core Web Vitals. To reduce page size:

  • Compress images and other media files.

  • Minimise the use of heavy scripts and third-party libraries.

  • Remove unnecessary plugins and widgets.

Role of Web Hosting

Choosing the Right Hosting Provider

Selecting a reliable hosting provider is crucial for maintaining optimal Core Web Vitals. Look for providers that offer:

  • High uptime guarantees.

  • Fast server response times.

  • Scalable resources to handle traffic spikes.

Importance of Server Location

The location of your server can affect load times, especially for international users. To improve performance:

  • Choose a hosting provider with data centres close to your target audience.

  • Consider using a Content Delivery Network (CDN) to distribute content globally.

Content Delivery Network (CDN)

How CDNs Help Improve Core Web Vitals

CDNs can significantly enhance Core Web Vitals by:

  • Reducing latency by serving content from servers closer to the user.

  • Decreasing load times through caching and efficient content delivery.

  • Balancing traffic loads to prevent server overloads.

Best Practices for Using a CDN

To maximise the benefits of a CDN:

  • Cache static content, such as images, CSS, and JavaScript files.

  • Use a CDN with a broad network of edge servers.

  • Regularly update and purge outdated content from the CDN to ensure users receive the latest version of your site.

Optimising Images for Better Performance

Image Compression

Image compression is crucial for reducing load times and improving Core Web Vitals. By compressing images, you decrease their file size without sacrificing quality, resulting in faster loading pages. Tools like TinyPNG and JPEGoptim can help compress images effectively.

Appropriate Image Formats

Choosing the right image format is essential for performance. For example:

  • JPEG: Best for photographs and images with many colours.

  • PNG: Ideal for images with transparency or fewer colours.

  • WebP: A modern format that provides superior compression for both lossless and lossy images, recommended for most scenarios.

Lazy Loading for Better Load Times

What is Lazy Loading?

Lazy loading is a technique that defers the loading of images and other non-critical resources until they are needed. This improves initial load times and reduces the amount of data that needs to be loaded upfront.

Implementing Lazy Loading

To implement lazy loading:

  • Use the loading="lazy" attribute on img tags in HTML.

  • Employ JavaScript libraries like LazyLoad for more advanced implementations and greater control over lazy loading behaviour.

Impact of JavaScript on Core Web Vitals

Minimising JavaScript Impact

JavaScript can significantly impact Core Web Vitals, particularly FID. To minimise its impact:

  • Reduce the amount of JavaScript loaded on the page.

  • Split large scripts into smaller, more manageable chunks.

  • Avoid long-running JavaScript tasks that block the main thread.

Async and Defer Attributes

Using the async and defer attributes for JavaScript can help improve loading performance:

  • Async: Downloads the script file while the HTML document is parsing, then executes it as soon as it’s available.

  • Defer: Downloads the script file while the HTML document is parsing, but waits to execute it until the document has finished parsing.

Importance of a Fast and Reliable Internet Connection

User Perception

A fast and reliable internet connection is essential for maintaining a good user experience. Slow connections can lead to longer load times, affecting user satisfaction and engagement. Users are more likely to abandon a site if it takes too long to load, which can negatively impact your Core Web Vitals and overall SEO performance.

Ensuring Consistent Speeds

To ensure consistent speeds:

  • Monitor your website’s performance regularly using tools like Google Analytics and PageSpeed Insights.

  • Optimise your site to load quickly even on slower connections by minimising the size of files and resources.

  • Use a CDN to deliver content from servers closest to the user, reducing latency and improving load times.

Case Studies of Improved Core Web Vitals

Examples from Industry Leaders

Several industry leaders have successfully improved their Core Web Vitals, resulting in better user experiences and higher search rankings. For example, UpLink SEO company in east London worked with various clients to enhance their site performance. One notable client, a local e-commerce store based at Liverpool Rd, London N1 0RR, saw their LCP improve from 4 seconds to 2 seconds by optimising their images and implementing lazy loading. Another client based near Angel Undeground Station, a blog site, reduced their CLS by 50% through better use of CSS and reserving space for ads and images.

Key Takeaways

From these case studies, we can extract several key takeaways:

  • Image Optimisation: Compressing and choosing the right formats can significantly improve LCP.

  • Lazy Loading: Deferring the loading of non-critical resources can enhance initial load times.

  • CSS Optimisation: Properly managing CSS and reserving space for dynamic content helps reduce CLS.

  • JavaScript Management: Minimising and optimising JavaScript can improve FID and overall page responsiveness.

Monitoring and Maintenance

Regular Audits

Regular audits are crucial to maintaining optimal Core Web Vitals. Use tools like Google PageSpeed Insights, Lighthouse, and the Web Vitals Extension to periodically check your site’s performance. Identify and fix issues promptly to ensure consistent user experience and high search rankings.

Keeping Up with Updates

The digital landscape is constantly evolving, and so are the standards for Core Web Vitals. Stay informed about the latest updates and best practices by following industry news, attending webinars, and participating in SEO communities. Regularly update your site to align with new guidelines and maintain competitive performance.

Future of Core Web Vitals in SEO

Anticipating Changes

Core Web Vitals are expected to play an increasingly important role in SEO. Google continues to refine its algorithms to prioritise user experience, meaning these metrics will likely become more significant. Anticipate changes by staying informed about Google’s updates and preparing to adapt your optimisation strategies accordingly.

Preparing for Future Updates

To prepare for future updates:

  • Stay Informed: Follow SEO blogs, Google announcements, and industry experts to keep abreast of upcoming changes.

  • Be Proactive: Regularly review and optimise your site’s performance, even if it currently meets the standards.

  • Invest in Quality: Focus on providing high-quality, user-friendly content and experiences that align with Core Web Vitals metrics.


What are the 3 pillars of Core Web Vitals?

The three pillars of Core Web Vitals are:

  • Largest Contentful Paint (LCP): Measures loading performance. A good LCP score is 2.5 seconds or less.

  • First Input Delay (FID): Measures interactivity. A good FID score is less than 100 milliseconds.

  • Cumulative Layout Shift (CLS): Measures visual stability. A good CLS score is less than 0.1.

How much do Core Web Vitals affect SEO?

Core Web Vitals significantly impact SEO as they are part of Google's ranking factors. Websites that perform well on these metrics tend to rank higher in search results. This is because Core Web Vitals improve user experience, which is a priority for Google’s search algorithms.

What are the four Core Web Vitals?

Currently, there are three Core Web Vitals: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). However, there is often confusion due to the inclusion of additional web performance metrics such as Time to First Byte (TTFB) and First Contentful Paint (FCP) in broader discussions about web performance.

What is the CWV score in SEO?

CWV (Core Web Vitals) score in SEO refers to the evaluation of a website's performance based on the Core Web Vitals metrics: LCP, FID, and CLS. These scores are used by Google to assess the quality of user experience provided by the site. High CWV scores can positively affect a site's search engine rankings.

How do I pass Core Web Vitals?

To pass Core Web Vitals:

  • Optimise LCP: Improve server response times, use efficient caching, and optimise images.

  • Reduce FID: Minimise JavaScript execution, use web workers, and defer non-critical JavaScript.

  • Minimise CLS: Reserve space for images and ads, avoid inserting content above existing content, and implement animations carefully.

What is the purpose of Core Web Vitals?

The purpose of Core Web Vitals is to measure and ensure a good user experience on web pages. These metrics focus on key aspects of user experience such as loading performance, interactivity, and visual stability, helping site owners and developers create more user-friendly websites.

Core Web Vitals are essential in SEO because they directly impact user experience and search engine rankings. These metrics—Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS)—measure how quickly a page loads, how responsive it is, and how stable the content is as it loads. A site that performs well in these areas ensures visitors have a smooth, fast, and enjoyable experience. Google prioritises such sites, meaning a strong performance in Core Web Vitals can lead to higher search rankings, increased visibility, and more organic traffic. Focusing on Core Web Vitals is not just about meeting Google's standards; it's about creating a better, more user-friendly web.

For more information, call our SEO company in London on: 020 7183 5137 or email

Address: 128 City Rd, London EC1V 2NX

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