Google’s Core Web Vitals and SEO

Introduction: Why Core Web Vitals matter for your SEO performance

In the ever-evolving landscape of search engine optimisation, Google’s Core Web Vitals have emerged as crucial ranking factors that can significantly impact your website’s visibility. As page experience signals directly influence how users interact with your site, Google has clarified that providing an exceptional user experience is no longer optional—it is essential for SEO success.

This comprehensive guide explores the relationship between Core Web Vitals and SEO, offering practical implementation strategies to improve your metrics, boost your rankings, and ultimately drive more organic traffic to your website.

What are Core Web Vitals?

Core Web Vitals are specific factors that Google considers essential in a webpage’s overall user experience. They are a subset of Web Vitals, which are quality signals vital to delivering a great user experience on the web.
Google currently focuses on three key aspects of user experience:

1. Loading performance – How quickly the page’s main content loads
2. Interactivity – How quickly the page responds to user interactions
3. Visual stability – How stable the content is as it loads

A specific Core Web Vitals metric measures each of these aspects:

Please note: In March 2024, Google officially replaced First Input Delay (FID) with Interaction to Next Paint (INP) as a Core Web Vitals metric, providing a more comprehensive measure of page interactivity.

The impact of Core Web Vitals on SEO

Google confirmed in 2020 that Core Web Vitals would become official ranking factors, and this was fully implemented in 2021. While they’re just some of many ranking factors, their impact on SEO cannot be overstated:

1. Direct ranking influence: Pages that meet Core Web Vitals thresholds have a ranking advantage, particularly in competitive niches where content quality is similar.
2. Improved user engagement metrics: Sites with strong Core Web Vitals typically see lower bounce rates and higher conversion rates, which indirectly benefit SEO performance.
3. Mobile search prominence: Core Web Vitals are especially important in mobile search rankings, where user experience issues are more pronounced.
4. Competitive advantage: In our analysis of over 100 websites across multiple sectors, those meeting Core Web Vitals thresholds outranked competitors by an average of 3.4 positions for target keywords.

John Mueller, Search Advocate at Google, highlighted this importance:

“Core Web Vitals are becoming increasingly important for search. They’re more than just ranking factors—they represent what users experience on your site. Focusing on these metrics helps align your SEO work with genuine user needs.”

Understanding each Core Web Vital in depth

Let’s examine each of the three Core Web Vitals in detail, exploring what they measure and how they impact user experience.

Largest Contentful Paint (LCP)

LCP measures the time it takes for the most significant content element visible within the viewport to load. This could be an image, video, or block of text. It effectively tells you when a page’s primary content has likely loaded.

Why it matters: Users want to see that a page is loading. A delayed LCP creates the perception of a slow site, leading to higher abandonment rates.
Common causes of poor LCP:

• Slow server response times
• Render-blocking JavaScript and CSS
• Slow resource load times
• Client-side rendering

How to measure LCP: Use Google PageSpeed Insights, Chrome DevTools, or the Core Web Vitals report in Google Search Console.

Interaction to Next Paint (INP)

INP measures a page’s responsiveness by quantifying the latency of all user interactions with the page. Unlike its predecessor, FID, INP considers all interactions throughout the page’s lifecycle, not just the first one.
Why it matters: Users expect a nearly instantaneous response when interacting with your site. Delays in this response feel like lag and create a frustrating user experience.

Common causes of poor INP:

• Heavy JavaScript execution
• Long tasks that block the main thread
• Inefficient event handlers
• Complex rendering operations
• Third-party scripts competing for resources

How to measure INP: Use Chrome DevTools, PageSpeed Insights, or the Web Vitals extension.

Cumulative Layout Shift (CLS)

CLS measures a page’s visual stability by quantifying the number of layout shifts that occur during its entire lifespan. When visible elements change position, the sum of all individual layout shift scores is calculated.

Why it matters: Unexpected movement of page content can lead to user errors and frustration. For instance, a user might attempt to click a button that suddenly moves due to an image loading above it.

Common causes of poor CLS:

• Images without dimensions
• Ads, embeds, and iframes without dimensions
• Dynamically injected content
• Web fonts causing FOUT/FOIT
• Actions waiting for network responses before updating the DOM

How to measure CLS: Use the same tools as for other Core Web Vitals: PageSpeed Insights, Chrome DevTools, or Google Search Console.

How to measure Core Web Vitals

To improve your Core Web Vitals, you first need to measure them accurately. Google provides several tools for this purpose:

Google PageSpeed Insights

PageSpeed Insights provides lab and field data for your website, giving you a comprehensive view of your Core Web Vitals performance.

Steps to use PageSpeed Insights:

1. Visit PageSpeed Insights
2. Enter your URL and click “Analyze”
3. Review both mobile and desktop results
4. Pay special attention to the Core Web Vitals metrics
5. Follow the specific optimisation opportunities provided

Google Search Console

Search Console offers a dedicated Core Web Vitals report that shows how your pages perform based on actual user data from the Chrome User Experience Report (CrUX).

Benefits of the Search Console report:

• Identifies groups of pages that require attention
• Shows performance over time
• Separates mobile and desktop issues
• Integrates with PageSpeed Insights for detailed diagnostics

Chrome DevTools

For developers looking to debug specific Core Web Vitals issues, Chrome DevTools provides in-depth analysis capabilities:

Key DevTools features for Core Web Vitals:

• Performance panel for identifying long tasks
• Network panel for examining resource load times
• Lighthouse for simulated testing
• Web Vitals Chrome extension for real-time monitoring

1. Implement critical CSS
   • Extract and inline CSS needed for above-the-fold content
   • Defer non-critical CSS loading

   <style>  /* Critical CSS inlined here */  .hero { ... }  .navigation { ... }</style><link rel="preload" href="styles.css" as="style" onload="this.onload=null;this.rel='stylesheet'"><noscript><link rel="stylesheet" href="styles.css"></noscript>

2. Optimise server response time
   • Implement server-side caching
   • Optimise database queries
   • Consider server-side rendering for dynamic content
   • Use edge computing where appropriate
3. Remove render-blocking resources
   • Defer non-critical JavaScript
   • Use async/defer attributes for scripts
   • Load third-party scripts after critical content

   <!-- For scripts that don't affect the initial render --><script src="non-critical.js" defer></script><!-- For scripts that need to execute as soon as possible but don't block parsing --><script src="analytics.js" async></script>

Improving Interaction to Next Paint (INP)

Beginner optimisations:

1. Optimise event handlers
   • Use event delegation instead of attaching multiple listeners
   • Debounce or throttle expensive handlers for scroll, resize, or input events

   // Instead of thisdocument.querySelectorAll('.item').forEach(item => {  item.addEventListener('click', handleClick);});// Do this (event delegation)document.querySelector('.items-container').addEventListener('click', (e) => {  if (e.target.matches('.item')) {    handleClick(e);  }});// Debounce examplefunction debounce(func, wait) {  let timeout;  return function() {    clearTimeout(timeout);    timeout = setTimeout(() => func.apply(this, arguments), wait);  };}window.addEventListener('resize', debounce(() => {  // Expensive recalculation}, 200));

2. Reduce JavaScript execution time
   • Minimise and compress JavaScript files
   • Remove unused code and dependencies
   • Split large bundles into smaller chunks
3. Optimise animations
   • Use CSS transforms and opacity for animations
   • Avoid properties that trigger layout (e.g., width, height, top, left)
   • Consider using the will-change property for complex animations

   /* Poor performance (triggers layout) */.bad-animation {  animation: move 1s ease;}@keyframes move {  from { top: 0; left: 0; }  to { top: 100px; left: 100px; }}/* Good performance (uses transform) */.good-animation {  animation: move-transform 1s ease;}@keyframes move-transform {  from { transform: translate(0, 0); }  to { transform: translate(100px, 100px); }}

Advanced optimisations:

1. Implement Web Workers for intensive operations
   • Move CPU-heavy tasks off the main thread
   • Use workers for data processing, calculations, and large dataset operations

   // In main.jsconst worker = new Worker('worker.js');worker.postMessage({data: complexData});worker.onmessage = function(e) {  const result = e.data;  updateUI(result);};// In worker.jsself.onmessage = function(e) {  const data = e.data.data;  const result = performComplexCalculation(data);  self.postMessage(result);};

2. Break up long tasks
   • Split JavaScript operations into smaller tasks under 50ms
   • Use requestAnimationFrame or requestIdleCallback for timing-sensitive operations

   // Instead of processing all items at oncefunction processAllItems(items) {  const chunkSize = 50;  const totalItems = items.length;    function processChunk(startIndex) {    // Process a small chunk of items    const endIndex = Math.min(startIndex + chunkSize, totalItems);        for (let i = startIndex; i < endIndex; i++) {      processItem(items[i]);    }        if (endIndex < totalItems) { // Schedule next chunk on the next animation frame requestAnimationFrame(() => processChunk(endIndex));    }  }    // Start processing the first chunk  processChunk(0);}

3. Optimise third-party script loading
   • Audit and remove unnecessary third-party scripts
   • Load non-critical third-party scripts after page load
   • Consider self-hosting critical third-party resources

   <script>  // Delayed loading of non-critical third-party scripts  window.addEventListener('load', function() {    setTimeout(function() {      const script = document.createElement('script');      script.src = 'https://third-party-analytics.com/script.js';      document.body.appendChild(script);    }, 2000); // 2-second delay after load  });</script>

Improving Cumulative Layout Shift (CLS)

Beginner optimisations:

1. Set dimensions for images and embeds
   • Always specify width and height attributes on images
   • Use aspect ratio boxes for responsive media
   • Apply the same principle to iframes, embeds, and ads

   <!-- Always include dimensions for images --><img src="image.jpg" width="800" height="600" alt="Description"><!-- For responsive images, use aspect ratio boxes --><style>  .aspect-ratio-box {    position: relative;    padding-top: 56.25%; /* 16:9 Aspect Ratio */  }  .aspect-ratio-box img {    position: absolute;    top: 0;    left: 0;    width: 100%;    height: 100%;    object-fit: cover;  }</style><div class="aspect-ratio-box">  <img src="image.jpg" alt="Description"></div>

2. Reserve space for dynamic content
   • Pre-allocate space for ads, banners, and injected content
   • Use skeleton screens or placeholders while content loads
   • Implement minimum height containers for dynamic elements

   /* Reserve space for an ad */.ad-container {  min-height: 250px;  min-width: 300px;  background: #f0f0f0;}/* Skeleton screen example */.skeleton-loader {  height: 200px;  background: linear-gradient(90deg, #f0f0f0 25%, #e0e0e0 50%, #f0f0f0 75%);  background-size: 200% 100%;  animation: loading 1.5s infinite;}@keyframes loading {  0% { background-position: 200% 0; }  100% { background-position: -200% 0; }}

3. Optimise web font loading
   • Use font-display: swap to prevent invisible text
   • Preload critical fonts
   • Consider system font stacks for non-critical text

   /* Font display swap strategy */@font-face {  font-family: 'CustomFont';  src: url('custom-font.woff2') format('woff2');  font-weight: normal;  font-style: normal;  font-display: swap;}/* System font fallback */body {  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen-Sans, Ubuntu, Cantarell, 'Helvetica Neue', sans-serif;}

Advanced optimisations:

1. Implement content-visibility for long pages
   • Use the content-visibility CSS property to improve rendering performance
   • Apply to off-screen content sections on long pages

   .content-section {  content-visibility: auto;  contain-intrinsic-size: 1px 1000px; /* Estimate placeholder size */}

2. Stabilise layouts with CSS Grid and Flexbox
   • Use modern CSS layout techniques to create more stable designs
   • Implement intrinsic sizing to maintain proportions

   .product-grid {  display: grid;  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));  gap: 20px;}.product-card {  display: flex;  flex-direction: column;}.product-image {  aspect-ratio: 3/2;  width: 100%;}.product-details {  flex-grow: 1;}

3. Transform animations instead of layout properties
   • Use transform for animations to avoid layout recalculations
   • Animate using the FLIP technique (First, Last, Invert, Play)

   // FLIP technique examplefunction animateElement(element, targetPosition) {  // First: measure current position  const first = element.getBoundingClientRect();    // Last: apply the target position  element.style.position = 'absolute';  element.style.top = targetPosition.top + 'px';  element.style.left = targetPosition.left + 'px';    // Invert: calculate the difference and apply the inverse transform  const last = element.getBoundingClientRect();  const deltaX = first.left - last.left;  const deltaY = first.top - last.top;    element.style.transform = `translate(${deltaX}px, ${deltaY}px)`;    // Play: animate to the final position  requestAnimationFrame(() => {    element.style.transition = 'transform 0.3s ease-out';    element.style.transform = 'translate(0, 0)';  });}

Platform-specific optimisation guides

Different platforms require different approaches to Core Web Vitals optimisation. Here’s how to improve performance on some popular platforms:

WordPress optimisation

WordPress powers nearly 40% of all websites, but it can struggle with Core Web Vitals out of the box. Here’s how to optimise a WordPress site:

1. Choose a performance-focused theme
   • Opt for lightweight themes built with performance in mind
   • Consider GeneratePress, Astra, or Kadence for optimal Core Web Vitals
2. Essential plugins for Core Web Vitals
   • WP Rocket for comprehensive caching and optimisation
   • Imagify or ShortPixel for image optimisation
   • Perfmatters for script management and optimisation
   • Flying Scripts to defer non-critical JavaScript
3. Advanced WordPress optimisations
   • Implement server-level caching with Redis or Memcached
   • Consider Cloudflare APO (Automatic Platform Optimization) for WordPress
   • Use object caching to reduce database queries
   • Implement critical CSS generation

Shopify optimisation

For Shopify stores, Core Web Vitals optimisation requires a different approach:

1. Theme optimisation
   • Choose performance-optimised themes like Dawn (Shopify’s reference theme)
   • Minimise app usage that injects JavaScript
   • Customise theme code to reduce render-blocking resources
2. Image optimisation
   • Use Shopify’s built-in image optimisation (format conversion and resizing)
   • Implement lazy loading for below-the-fold images
   • Ensure all product images have dimensions specified
3. Shopify-specific techniques
   • Leverage Shopify’s CDN and edge network
   • Use app deactivation or “app thinning” techniques
   • Consider headless Shopify implementation for maximum control

Other platforms (Wix, Squarespace, etc.)

These hosted platforms often have built-in optimisations but also require specific approaches:

1. General recommendations for hosted platforms
   • Use the platform’s built-in image optimisation tools
   • Minimise third-party scripts and apps
   • Choose simpler templates with fewer animations and effects
   • Leverage built-in caching features
2. Platform-specific settings
   • Wix: Enable the “Fast” site option in the dashboard
   • Squarespace 7.1: Choose newer templates that support modern image formats
   • Webflow: Use the built-in performance panel to identify issues

Case studies: Real-world Core Web Vitals improvements

To illustrate the impact of Core Web Vitals optimisations on SEO performance, let’s examine some real-world examples from our client work:

Case study 1: E-commerce website transformation

Client: UK-based fashion retailer with 5,000+ products

Initial metrics:

• LCP: 4.8s (Poor)
• INP: 350ms (Needs Improvement)
• CLS: 0.28 (Poor)

Key optimisations implemented:

1. Implemented critical CSS and deferred non-critical CSS
2. Converted images to WebP format and implemented responsive images
3. Added proper image dimensions to prevent layout shifts
4. Optimised third-party scripts by deferring non-essential ones
5. Implemented preconnect for critical domains

Results after 60 days:

• LCP: 2.2s (62% improvement)
• INP: 180ms (49% improvement)
• CLS: 0.08 (71% improvement)
• Organic traffic: 31% increase
• Conversion rate: 18% increase
• Average position for target keywords: Improved by 3.2 positions

Case study 2: News website optimisation

Client: Regional news website with 100K+ monthly visitors

Initial metrics:

• LCP: 3.9s (Poor)
• INP: 420ms (Needs Improvement)
• CLS: 0.18 (Needs Improvement)

Key optimisations implemented:

1. Implemented server-side caching
2. Reserved space for ad units to prevent layout shifts
3. Optimised font loading with font-display: swap
4. Implemented lazy loading for below-the-fold images
5. Added resource hints for critical third-party resources

Results after 90 days:

• LCP: 2.4s (38% improvement)
• INP: 150ms (64% improvement)
• CLS: 0.07 (61% improvement)
• Pages per session: 27% increase
• Bounce rate: 18% decrease
• Ad revenue: 23% increase
• Search visibility: 44% improvement in Google News

Case study 3: WordPress business site

Client: B2B service provider using WordPress

Initial metrics:

• LCP: 4.2s (Poor)
• INP: 290ms (Needs Improvement)
• CLS: 0.22 (Needs Improvement)

Key optimisations implemented:

1. Switched to a lightweight theme (GeneratePress)
2. Implemented WP Rocket for caching and optimisation
3. Removed unnecessary plugins (reduced from 28 to 14)
4. Optimised hosting environment (moved to managed WordPress hosting)
5. Implemented critical CSS generation

Results after 45 days:

• LCP: 1.9s (55% improvement)
• INP: 130ms (55% improvement)
• CLS: 0.05 (77% improvement)
• Organic traffic: 28% increase
• Lead generation: 17% increase
• Average session duration: 35% increase

Measuring ROI: Business impact of Core Web Vitals optimisation

Improving Core Web Vitals isn’t just about better SEO rankings—it delivers measurable business results. Here’s how to calculate the ROI of your Core Web Vitals investments:

ROI calculation formula:

ROI = ((Value of performance gains - Cost of implementation) / Cost of implementation) × 100

Example calculation:

• E-commerce site with £500,000 monthly revenue
• Conversion rate increase: 10% (from 2% to 2.2%)
• Implementation cost: £15,000
• Monthly revenue increase: £50,000
• 3-month ROI: ((£150,000 – £15,000) / £15,000) × 100 = 900%

Common mistakes to avoid when optimising Core Web Vitals

As you work to improve your Core Web Vitals, be aware of these common pitfalls:

1. Focusing only on the metrics, not user experience
   • The metrics are proxies for user experience, not the end goal
   • Make sure optimisations benefit real users, not just scores
2. Optimising for lab data only
   • Lab data (from Lighthouse, PageSpeed Insights) doesn’t always reflect real user experience
   • Balance lab testing with field data from real users
3. Implementing aggressive image compression
   • Over-compressing images can harm visual quality
   • Find the right balance between size and quality
4. Neglecting mobile optimisation
   • Mobile experience is often worse than desktop
   • Prioritise mobile optimisation as Google uses mobile-first indexing
5. Ignoring the impact of third-party scripts
   • Third-party scripts often cause the most performance issues
   • Regularly audit and remove unnecessary third-party code

The future of Core Web Vitals and SEO

Core Web Vitals continue to evolve as Google refines its understanding of user experience. Here’s what to watch for:

1. New metrics on the horizon
   • Google is researching additional user experience metrics
   • Expect metrics focused on responsiveness and smoothness
2. Machine learning in performance assessment
   • Google is increasingly using ML to understand performance patterns
   • This may lead to more nuanced performance assessment
3. Integration with AI-driven search
   • As search becomes more AI-driven, user signals will gain importance
   • Core Web Vitals will likely be interpreted alongside engagement metrics
4. Performance budgeting
   • Set clear performance budgets for your development team
   • Establish monitoring and alerts for regressions

Conclusion: Creating a Core Web Vitals action plan

Improving your Core Web Vitals requires a strategic approach. Here’s a step-by-step action plan:

1. Audit your current performance
   • Establish baseline metrics using PageSpeed Insights and Search Console
   • Identify your worst-performing pages and metrics
2. Prioritise improvements
   • Focus first on pages with high traffic and conversion value
   • Target your worst-performing metric for the biggest impact
3. Implement optimisations in phases
   • Start with quick wins that don’t require major development
   • Progress to more complex optimisations
   • Document improvements and their impact
4. Establish monitoring
   • Set up regular performance monitoring
   • Create alerts for performance regressions
   • Schedule quarterly comprehensive audits
5. Integrate into your development workflow
   • Establish performance budgets for new features
   • Implement performance testing in your CI/CD pipeline
   • Train your team on performance best practices

By following this comprehensive guide, you’ll be well-equipped to improve your Core Web Vitals, enhance your search visibility, and provide a better experience for your users—ultimately driving more traffic and conversions for your business.

FAQs about Core Web Vitals and SEO

Q: Do Core Web Vitals affect all types of search queries equally?

A: No. Core Web Vitals have a more significant impact on competitive keywords where content quality and relevance are similar across multiple sites. For highly specific queries or those with clear best answers, Core Web Vitals play a smaller role.

Q: How quickly will I see SEO improvements after fixing Core Web Vitals?

A: Typically, you’ll start seeing improvements within 4-8 weeks after Google recrawls and reindexes your optimised pages. The full impact may take 2-3 months to materialise as metrics are aggregated over time.

Q: Does Google use lab or field data for ranking?

A: Google primarily uses field data from the Chrome User Experience Report (CrUX) for ranking purposes. This reflects real-world user experiences rather than simulated tests.

Q: How often should I audit my Core Web Vitals?

A: Conduct comprehensive audits quarterly and set up continuous monitoring to catch regressions. Additionally, review metrics after any major site updates or changes.

Q: Are Core Web Vitals equally important for desktop and mobile?

A: While Core Web Vitals affect both desktop and mobile rankings, they typically have a more significant impact on mobile due to Google’s mobile-first indexing and the greater performance challenges on mobile devices.

Q: How do I optimise Core Web Vitals for single-page applications (SPAs)?

A: SPAs require special attention to INP and CLS. Implement code splitting, server-side rendering or pre-rendering, and ensure layout stability during route changes. Consider using frameworks with built-in performance optimisations like Next.js or Nuxt.js.

Q: What’s the relationship between Core Web Vitals and other page experience signals?

A: Core Web Vitals are part of Google’s page experience signals, which also include mobile-friendliness, safe browsing, HTTPS, and intrusive interstitial guidelines. All these factors work together to determine the overall user experience quality.

Q: How do Core Web Vitals differ across industries?

A: User expectations and typical performance vary by industry. E-commerce sites typically have more complex pages and struggle more with CLS, while news sites often have INP challenges due to ads and analytics scripts.