Core Web Vitals 2025: Optimizing LCP, INP and CLS for SEO and User Experience
Published on — Updated on — By Equipe SEO 5.0
In an increasingly competitive digital landscape, user experience has become a fundamental pillar for online success. Google, recognizing this importance, has consolidated the Core Web Vitals as crucial metrics to evaluate the quality of browsing experience. Since 2021, these indicators have been confirmed ranking factors, and their relevance is only expected to grow in 2025. According to a Deloitte study, a 0.1 second improvement in site load time can increase conversion rates by up to 8%. This shows that optimizing Core Web Vitals is not just an SEO concern, but a vital strategy for business growth. This practical guide will dive into the LCP, INP and CLS metrics, providing a detailed roadmap to optimize them, with a focus on practical examples for WordPress and custom sites. ## Understanding the Core Web Vitals: LCP, INP and CLS The Core Web Vitals are a set of three specific metrics that measure the user experience on a website: Largest Contentful Paint (LCP), Interaction to Next Paint (INP) and Cumulative Layout Shift (CLS). Each of them addresses a different aspect of the experience — loading, interactivity and visual stability, respectively. > "Core Web Vitals are a set of real-world, user-centered metrics that quantify key aspects of the web user experience. They measure dimensions of web usability such as loading performance, interactivity, and visual stability of content, and are ranking factors for Google." - Google Search Central A deep understanding of each of these metrics is the first step toward effective optimization. ### Largest Contentful Paint (LCP): Perceived Speed LCP measures the time it takes for the largest visible content element in the viewport to be rendered. This element can be an image, a video, a large block of text, or any other element that occupies the largest portion of the initial screen. LCP is crucial because it reflects the perceived loading speed for the user. A fast LCP means the user sees the main content quickly, which improves first impressions and reduces the likelihood of abandonment. #### LCP Benchmarks: | Status | Time (seconds) | | :--------------- | :--------------- | | Good | ≤ 2.5 | | Needs Improvement| 2.5 - 4.0 | | Poor | > 4.0 | #### Main Causes of Poor LCP: * **Slow server response times:** Slow or misconfigured servers, low-quality hosting. * **Render-blocking resources:** Unoptimized JavaScript and CSS that delay rendering of the main content. * **Slow resource loading:** Large, unoptimized images and heavy videos. * **Client-side rendering:** Single Page Applications (SPAs) that rely heavily on JavaScript to render initial content. ### Interaction to Next Paint (INP): Interaction Responsiveness INP is the newest Core Web Vitals metric, replacing First Input Delay (FID) in March 2024. It measures the latency of all page interactions — from the moment the user clicks, taps, or types, until the browser is able to paint the next visual frame with the relevant UI update. INP assesses overall page responsiveness, ensuring user interactions are processed quickly and accompanied by immediate visual feedback. #### INP Benchmarks: | Status | Time (milliseconds) | | :--------------- | :-------------------- | | Good | ≤ 200 | | Needs Improvement| 200 - 500 | | Poor | > 500 | #### Main Causes of Poor INP: * **Long-running JavaScript:** Scripts that perform complex tasks and block the main thread for extended periods. * **Excessive network tasks:** Network requests that delay the UI response. * **Complex rendering:** DOM updates that require significant browser processing. * **Main thread blocking:** Caused by third-party scripts, tag managers or poorly optimized plugins. ### Cumulative Layout Shift (CLS): Visual Stability CLS measures the total sum of all individual layout shift scores for every unexpected layout shift that occurs during the lifetime of a page. A layout shift happens when a visible element changes position unexpectedly, causing a frustrating experience for the user (for example, a button that moves while the user is trying to click it). CLS is critical for usability, as unstable layouts can lead to accidental clicks and a feeling of lack of control. #### CLS Benchmarks: | Status | Score | | :--------------- | :-------- | | Good | ≤ 0.1 | | Needs Improvement| 0.1 - 0.25| | Poor | > 0.25 | #### Main Causes of Poor CLS: * **Images without dimensions:** Images that load without `width` and `height` attributes, causing the browser not to reserve space. * **Ads, embeds and iframes without dimensions:** External content that injects elements into the page without reserved space. * **Dynamically injected content:** Cookie banners, pop-ups or other elements that appear after initial load. * **Web fonts (FOIT/FOUT):** Fonts that load late, causing a layout shift when applied. ## How to Measure the Core Web Vitals: Tools and Methods Accurate measurement of Core Web Vitals is essential to identify problems and monitor optimization progress. There are several tools, each with its peculiarities and uses. ### Field Tools (Real User Monitoring - RUM): Field tools collect data from real users, providing a more accurate view of the experience across different devices and network conditions. * **Chrome User Experience Report (CrUX):** This is Google's official dataset for Core Web Vitals. It collects anonymous data from real Chrome users across millions of sites. CrUX is the data source Google uses to determine ranking based on Core Web Vitals. You can access CrUX data through PageSpeed Insights, Google Search Console and BigQuery. * **Google Search Console:** In the "Core Web Vitals" section, Search Console shows your site's performance based on CrUX data, categorizing URLs as "Good", "Needs Improvement" or "Poor" for each metric. * **Third-party RUM tools:** There are various paid solutions that offer detailed RUM monitoring, allowing segmentation by device type, geographic location and other factors. ### Lab Tools (Synthetic Monitoring): Lab tools simulate page loading in a controlled environment, which is useful for debugging and identifying specific issues. * **PageSpeed Insights:** This Google tool provides a comprehensive analysis of a URL, including field data (CrUX) and lab data (Lighthouse). It's one of the most accessible and complete tools for an initial analysis. * **Lighthouse:** Integrated into Chrome DevTools, Lighthouse lets you audit performance, accessibility, SEO and best practices. It provides detailed scores for each Core Web Vital and optimization recommendations. * **WebPageTest:** An advanced tool that allows testing page load from different locations, browsers and connection speeds, with detailed waterfall reports and loading videos. #### Case Study: LCP Improvement at The Washington Post In 2020, The Washington Post faced LCP challenges on its article pages. The site, rich in multimedia content and third-party scripts, frequently exceeded the 2.5 second threshold for a "good" LCP. The engineering team performed an in-depth analysis using Lighthouse and WebPageTest, identifying the main causes as: 1. **Unoptimized hero images:** Large, high-resolution images loading without optimization. 2. **Render-blocking CSS and JavaScript:** CSS and JS files that delayed above-the-fold rendering. 3. **Custom web fonts:** Fonts that caused delays in text display. To address these issues, they implemented the following strategies: * **Image optimization:** They used modern image formats (WebP), lossless compression and responsive loading via `srcset`. * **Critical CSS and asynchronous JS loading:** They extracted critical CSS for above-the-fold content and inlined it directly in the HTML, deferring the rest of the CSS and JavaScript. * **Font preloading:** They used `rel="preload"` for web fonts to ensure they loaded as early as possible. * **Server optimization:** They improved CDN and server cache configuration. As a result, The Washington Post managed to reduce its average LCP to under 2 seconds on article pages, positively impacting user retention and visibility in Google Discover. This case demonstrates the importance of detailed analysis and applying technique-specific solutions for each metric. ## Practical Optimization of Core Web Vitals: Strategies and Tools Optimizing Core Web Vitals requires a multifaceted approach, combining front-end, back-end and infrastructure techniques. The C.O.R.E. Framework of SEO 5.0 emphasizes the importance of Continuous, Outcome-Oriented and Strategic optimization, and this applies perfectly to Core Web Vitals. ### Optimizing LCP (Largest Contentful Paint) The key to a fast LCP is ensuring the page's main content is loaded and rendered as quickly as possible. #### 1. Server and Hosting Optimization: * **Choose a quality hosting provider:** Slow servers are a bottleneck. A good provider with optimized infrastructure and data centers near your target audience is essential. * **Use a CDN (Content Delivery Network):** CDNs store copies of your content on geographically distributed servers, delivering it to users from the nearest server and reducing latency. * **Enable browser caching:** Configure HTTP cache headers so static resources are stored in the user's browser, speeding up subsequent visits. * **Optimize server response time (TTFB):** This may involve database optimizations, server-side code improvements and web server configuration. #### 2. Image and Media Optimization: * **Compress and resize images:** Use tools like TinyPNG, ImageOptim or WordPress plugins (Smush, Imagify) to compress images without perceptible quality loss. Resize images to the exact dimensions they'll be displayed at. * **Use modern image formats:** Formats like WebP and AVIF offer better compression and quality compared to JPEG and PNG. * **Responsive image loading:** Use the `srcset` attribute and the `