Core Web Vitals 2025 Guide: Optimize LCP, INP & CLS for SEO Success

Core Web Vitals are a set of real-user, field-measured metrics defined by Google that quantify key aspects of user experience on the web: loading performance, interactivity, and visual stability. Specifically, the three Core Web Vitals metrics are: Largest Contentful Paint (LCP), which measures the loading speed of the main content; Cumulative Layout Shift (CLS), which measures visual stability (layout shifts during page load); and First Input Delay (FID), an older interactivity metric which has been replaced by Interaction to Next Paint (INP) in 2024. To provide a good user experience, Google recommends that LCP occur within 2.5 seconds of when the page starts loading, CLS score be 0.1 or less (on a 0–1 scale), and INP (the latency of user interactions) be 200 milliseconds or less.

These thresholds are based on real-user data and represent a “good” user experience benchmark. For example, LCP values ≤2500 ms are considered good, while >4000 ms are poor; for INP (and formerly FID), ≤200 ms is good and >500 ms is poor; for CLS, ≤0.1 is good and >0.25 is poor. In practice, Google measures these metrics using both lab tools and its Chrome User Experience Report (CrUX) of real-world Chrome data. The field-data values are surfaced in tools like PageSpeed Insights and Search Console. (If you ever see “INP” reported, note that since March 2024, it has replaced FID as the interactivity metric.)

Core Web Vitals have been formally part of Google’s page experience ranking factors since 2021. Google’s documentation strongly recommends that site owners achieve good scores on these metrics “for success with Search” and notes that they “align with what our core ranking systems seek to reward.” In other words, faster, more stable pages tend to be rewarded in search rankings, though Google cautions that “good Core Web Vitals scores do not guarantee a top search ranking.” In short, Core Web Vitals are important both for SEO and for user experience – they capture how real users perceive page speed and smoothness, which directly impacts engagement and business outcomes.

Below, we explain each Core Web Vitals metric and how it is measured, describe recent updates (notably the switch from FID to INP), and detail how and why to optimize them. We discuss their strategic importance for SEO and conversions, review tools for measuring them, and give technical best practices for improving LCP, INP, and CLS. Finally, we cite real-world case studies showing how companies that optimized Core Web Vitals saw better business metrics.

Core Web Vitals Metrics: LCP, CLS, FID/INP

Largest Contentful Paint (LCP) measures loading performance. It records the time from when the page starts to load to when the largest content element (e.g., a hero image, large text block, or video) is rendered in the viewport. In practical terms, LCP tells you how long users wait to see the main content. Google recommends that sites strive for LCP ≤ 2.5 seconds for 75% of page loads (the “good” threshold). Anything over 4 seconds is considered poor (needs improvement). To improve LCP, you need to optimize the critical loading path: serve HTML faster, load the key image/text quickly, and avoid delays (detailed below). For example, Amazon OSS images or CSS often dominate LCP, so preloading or compressing them can help.

Cumulative Layout Shift (CLS) measures visual stability. It quantifies unexpected layout shifts during page load by multiplying the size of the content that moved by the distance it moved. A CLS score of 0 means no shifts; higher scores up to 1.0 are worse. For good UX, Google advises keeping CLS ≤ 0.1. Layout shifts are jarring to users (e.g., text or buttons jumping around) and are typically caused by images, ads, or iframes loading without reserved space or by late-loading fonts that change text size. Best practices to improve CLS include reserving space with width/height (or CSS aspect ratio) on images/videos, setting explicit sizes for ads/embeds, and using CSS transforms for animations instead of layout-affecting properties. (More details below.)

First Input Delay (FID) was the original interactivity metric: it measured the delay from when a user first interacts with the page (e.g., clicks a button) to when the browser begins processing event handlers, reflecting responsiveness. A good FID was ≤100 ms. However, FID only considered the first input and did not account for later interactions. In 2024, Google replaced FID with Interaction to Next Paint (INP) to better assess overall responsiveness. INP measures the latency of user interactions throughout the page’s lifecycle: it captures the worst (or 98th percentile for very interactive sites) of all interaction delays (input delay + event handling time + time to the next frame paint). Thus, INP is a more comprehensive metric of responsiveness. To provide a good experience, pages should aim for INP ≤200 ms at the 75th percentile of loads.

In summary, Core Web Vitals cover loading speed (LCP), interactivity (INP), and visual stability (CLS). Google’s thresholds (e.g., LCP ≤2.5 s, INP ≤200 ms, CLS ≤0.1) have remained stable into 2024–2025. The big change was the March 2024 transition from FID to INP: Google Search Console and performance tools now report INP instead of FID.

Why Core Web Vitals Matter: SEO, UX, and Business Impact

Core Web Vitals are not just technical metrics; they are closely tied to user satisfaction and business outcomes. Google’s teams have emphasized that fast, seamless page experiences delight users and build loyalty, which in turn leads to better KPIs. For instance, one Google case study notes that delivering “fast and seamless navigation experience[s] delight users and help turn them into loyal and returning customers.” Studies of real websites consistently show that improving Core Web Vitals leads to measurable gains: faster load times, reduced bounce rates, and boosted conversions. In one analysis, Renault’s data showed that a 1-second improvement in LCP was associated with a 13% increase in conversion rate and a 14 percentage-point drop in bounce rate. In practice, lowering LCP below 1.0 s yielded significantly better engagement on Renault’s pages.

From an SEO perspective, Core Web Vitals are part of Google’s Page Experience ranking signals. Since the mid-2021 “Page Experience” update, Google has used LCP, CLS, and INP (formerly FID) among many signals to assess whether a page provides a good user experience. Having good Core Web Vitals can give pages a modest ranking boost, especially when content quality is otherwise comparable. That said, Google cautions that CWV scores alone do not guarantee high rankings – they are just one of hundreds of signals. In other words, great Core Web Vitals can help SEO by complementing strong content and relevance, but they won’t replace it.

Strategically, Core Web Vitals optimization should be viewed as an investment in UX and conversion. For example, an analysis by Shopify found that improving a site’s LCP by 1 second led to a 14% increase in conversion rate and a 27% reduction in bounce rate (in contexts like Renault above). Another case study (Vodafone Italy) showed that after optimizing images, CSS, and server rendering to reduce LCP by 31%, the site saw 8% more sales and an 11% lift in cart-to-visit rate. Similarly, Swappie (an e-commerce retailer) improved its Core Web Vitals and saw 42% higher mobile revenue as a result. These and many other examples illustrate that faster, more stable sites drive better engagement, which translates into business metrics like sales or ad revenue.

In summary, optimizing for Core Web Vitals pays off by improving SEO visibility and, more importantly, by enhancing user experience. This leads to tangible business benefits such as higher click-through rates, longer session durations, and increased conversions. Keeping this strategic context in mind helps justify the effort needed to improve these metrics.

Measuring Core Web Vitals: Tools and Updates

To track and diagnose Core Web Vitals, a variety of tools are available, each with its use cases:

• PageSpeed Insights (PSI): Google’s online tool that analyzes a URL, providing both lab (Lighthouse) and field (CrUX) data. PSI displays your LCP, INP, and CLS scores and a pass/fail status based on the thresholds. It uses Lighthouse 12 (as of May 2024) to simulate a page load in the lab and also pulls real-user data from the Chrome UX Report. New PSI features include shareable report links (announced March 2023) and updated field metrics. Developers use PSI to get a quick diagnostic of CWV issues.
• Lighthouse: The open-source auditor that powers PSI. Lighthouse runs in Chrome DevTools (or via the CLI) to simulate loading the page and measure Core Web Vitals in a controlled (throttled) environment. Note that Lighthouse lab results may differ from field data (CrUX), but they provide actionable diagnostics (e.g., which resources are delaying LCP). In mid-2024, PSI/Lighthouse was updated to version 12.0. In that release, the PWA category was removed, but the Performance audits (including CWV) remain. PSI/Lighthouse also removed the experimental EXPERIMENTAL_INTERACTION_TO_NEXT_PAINT metric and now uses the standard INTERACTION_TO_NEXT_PAINT for INP.
• Chrome DevTools Performance Panel: In recent Chrome versions, the Performance panel has a “Live Metrics” view that shows LCP, CLS, and INP in real time as the page loads. Notably, Google has integrated the formerly stand-alone Web Vitals Chrome extension into DevTools. As of Chrome 132 (Jan 2025), the Web Vitals extension has been discontinued, and its features now appear in DevTools. Web developers can record a trace in DevTools and immediately see the page’s LCP, INP, and CLS values alongside the traditional performance waterfall. This is very useful for debugging specific pages interactively.
• Chrome UX Report (CrUX): A BigQuery dataset and API of anonymized field metrics from real Chrome users. CrUX collects LCP, INP, CLS (and other metrics like TTFB) for millions of origins, segmented by device type. Importantly, CrUX no longer provides FID data as of late 2024 (the final FID data was published in August 2024) because of the switch to INP. CrUX data is available via BigQuery or via the CrUX API and is also what powers the field-data sections of PSI and the Search Console report. For example, the Chrome UX Report release notes showed that in August 2024, over 85% of origins had “good” INP, and over 64% had good LCP. Webmasters can use the CrUX API to retrieve CWV data for their site or compare it to competitors.
• Google Search Console – Core Web Vitals Report: This report (in the Google Search Console dashboard) shows real-user CWV performance for your indexed pages. It groups pages by URL pattern and flags “Good,” “Needs improvement,” and “Poor” status for LCP, INP, and CLS based on CrUX data (Read more). You can drill down to see which issues (e.g., “LCP issue” or “CLS issue”) affect specific pages. The report only appears once a site has sufficient CrUX data for LCP and CLS. It’s a convenient way for SEO and marketing teams to monitor field performance trends over time.
• Web Vitals JavaScript Library: Google provides a lightweight web-vitals JS library that can be added to pages to capture Core Web Vitals in real-time and report them to analytics (e.g., Google Analytics or your backend). For example, Renault used this library to send web vitals to Google Analytics for deep analysis. This RUM approach gives the most accurate picture of the real user experience. Other RUM tools (like New Relic, Calibre, Cloudflare, etc.) can also report CWV. In fact, Google’s guidance suggests using any RUM solution to start measuring CWV in production and then analyzing slow interactions in the lab.
• Chrome Web Vitals Extension (deprecated): The Chrome Web Vitals extension was a handy way to see Core Web Vitals for the current page. It is now deprecated: Google ended its support in early 2025 and merged its features into DevTools. If you still have it installed, it will warn that it’s no longer updated. From January 2025 onward, use DevTools instead.

When interpreting results, remember that lab tools simulate conditions (e.g., throttled network/CPU) while field data reflect actual users (with varied devices and connections). A page might score well in a lab but still have field CLS issues due to third-party scripts or ads. Always use a combination of lab and RUM data. For example, PageSpeed Insights shows both the Lighthouse simulation result and the 28-day field data for each metric. Chrome DevTools Performance panel can overlay real CrUX data on a local trace. Search Console reports give historical field trends for your site. By cross-referencing these tools, you can diagnose and prioritize the biggest problems affecting your users.

Optimizing Largest Contentful Paint (LCP)

Optimizing LCP generally means making the page’s largest element (often an image or block of text) appear as quickly as possible. The LCP time consists of four subparts: time to first byte (TTFB), resource load delay, resource load duration, and element render delay. In practice, the largest chunks of LCP time are usually the TTFB (getting the HTML) and downloading the LCP resource (e.g., an image).

Illustration: a network loading timeline where the HTML document (blue) downloads first, followed by other resources; the green bar is the “LCP resource” (an image) whose end marks the LCP time. Optimizing LCP means shifting that green bar to the left (making it load earlier).

Key strategies to improve LCP include:

Preload the LCP resource: If the largest element is an image, video, or font, make sure the browser discovers it immediately. For example, if it’s an <img> element in your HTML, avoid lazy-loading it (don’t use loading=”lazy” for the LCP image). You can explicitly preload it with a high-priority hint:

<link rel="preload" as="image" href="hero-image.webp" fetchpriority="high">

• This ensures the browser starts fetching the image at the same time as it loads the main HTML. If the LCP is text requiring a web font, preload the font. The goal is that the LCP resource’s request starts no later than the first few resources on the page. (In fact, a good rule of thumb is the LCP resource should begin downloading at the same time as the very first resource loaded).
• Reduce server response time (TTFB): Nothing can load faster than the HTML itself. Optimize the time to the first byte by using fast hosting, CDN/CDN caching, and minimizing redirects. For dynamic sites, ensure critical HTML is cached or use pre-rendering/SSR. For example, Server-Side Rendering (SSR) or static generation ensures the HTML (and references to images) are delivered immediately, making the LCP image discoverable. (SSR adds some server load, but it greatly reduces delays caused by client-side rendering.) Use a Content Delivery Network (CDN) to bring servers physically closer to users and ensure that caching headers are set so repeat visits load fast from the cache.
• Optimize CSS and JS: Remove or defer render-blocking resources so that the browser can render the LCP element as soon as it arrives. Inline critical CSS for above-the-fold content and defer other styles. Similarly, move non-essential JavaScript to the bottom or use defer/async so that scripts don’t delay rendering. Any stylesheets or scripts in <head> block rendering, so trim them to the minimum needed. If using a heavy front-end framework, consider partial hydration or delaying non-critical scripts.
• Compress and optimize media: If the LCP element is an image or video, serve it in an optimized size and format. Use responsive images (via <img srcset>) so mobile users load smaller images. Use modern formats like WebP or AVIF to reduce file size. Also, an Image CDN can automatically resize and compress images on the fly for different devices. Inline very small LCP images as Data URLs (though use this sparingly since it prevents caching and can increase HTML size).
• Set efficient caching: Configure caching (via Cache-Control headers) so that returning visitors get static assets instantly from the cache (making the network load duration ~0). For the HTML itself, use CDNs or “stale-while-revalidate” if content changes infrequently.
• Host on the same origin and use preconnect: If your LCP resource is on another domain, the browser must open a new connection. You can use <link rel=”preconnect”> or host critical assets on the same origin to reuse connections. Chrome’s optimizations assume first-party resources load faster.

Overall, think of LCP optimization as a pipeline: server (TTFB) → HTML parsing (resource discovery) → network download (resource load) → rendering. Any delay in this chain postpones LCP. For example, delaying the image load by lazy-loading or hidden CSS moves the green “LCP” bar to the right without reducing overall work. The goal is to get each step done as soon as possible. Audit your page with DevTools or Lighthouse to find the LCP element and see which step is dominating its load time. Then, apply the practices above to shrink that step.

In summary, optimizing LCP involves loading the main content quickly: delivering HTML fast, preloading and prioritizing the largest element, deferring non-critical tasks, and minimizing resource sizes and distances. Many improvements come from fundamental web performance best practices like compression, caching, and reducing render-blocking code.

Optimizing Interactivity (INP)

Interaction to Next Paint (INP) replaces the old FID metric and evaluates how responsive a page feels for users. INP measures the latency of user interactions (e.g., clicks, taps, key presses) by adding up input delay, processing duration, and presentation delay. It reports the worst (or 98th percentile) delay across the page’s lifetime. To improve INP, the main objective is to minimize main-thread work around user input so that interactions can be handled immediately. Key strategies include:

• Reduce long tasks on the main thread: A common cause of input delay is that the browser’s main thread is busy (for example, parsing or executing large JavaScript bundles). Audit your app for “long tasks” (tasks >50 ms) using DevTools Performance or Lighthouse. Break up large bundles and lazy-load code so less is processed upfront. Consider using Web Workers for heavy computations. Even if your page appears rendered, it might still be executing scripts in the background, so defer or chunk non-essential scripts.
• Optimize event handlers: Once an interaction starts processing, you want the event callback to finish quickly. Keep event handlers (click, scroll, keypress, etc.) as lightweight as possible. If complex work must be done, use asynchronous patterns to yield to the browser. For example, you can split work using setTimeout or requestAnimationFrame so that the UI can update before continuing computation. A recommended pattern is to do only the minimal DOM update in the event handler (so the next frame’s visual changes happen soon) and offload any remaining logic (e.g., analytics, saving data) to a subsequent task. The web-vitals guide shows how requestAnimationFrame plus setTimeout can break up a rich text editor’s input processing so the UI updates immediately and other work happens afterward.
• Yield to the browser: If you cannot significantly reduce handler code, at least occasionally yield back to the main thread so the browser can respond to other inputs. For example, after 100ms of continuous work, you might await a new Promise(r => setTimeout(r,0)) to allow the browser to handle other events. This prevents one long task from blocking all interactions.
• Avoid layout thrashing: Layout thrashing (forced synchronous layouts) can stall rendering and thus inflate INP. This happens when JavaScript modifies the DOM/CSS and then immediately reads layout properties (e.g., .offsetHeight). Each read forces the browser to apply pending changes. To avoid this, batch DOM writes and reads separately and uses window.requestAnimationFrame to schedule reads. DevTools will flag these thrashing patterns (a red triangle icon).
• Minimize presentation delay: Even if input and processing are fast, the final painting of updates can be slow if rendering is heavy. A large DOM or complex page can make the browser’s paint take longer. To help, reduce DOM depth/complexity where possible, and consider using content-visibility: auto on off-screen sections to defer their rendering. That way, the browser only has to paint what’s visible. Also, avoid excessive CSS complexity or huge style sheets, which can slow down rendering.
• Use passive event listeners where appropriate: For example, for scroll or touch events, using {passive: true} can improve performance because the browser knows it won’t cancel scrolling.
• Avoid synchronous dialogs: Chrome 127+ treats alert(), prompt(), etc., as completing the interaction, which improved INP for sites using those dialogs. However, it’s generally better UX to avoid modal dialogs altogether and handle feedback in the page’s UI.

Overall, optimizing INP is about keeping the main thread free and breaking up work. The web.dev guide on INP emphasizes making input delays (time until event handlers start) and processing durations as small as possible. Tools like Lighthouse (Interaction to Next Paint audit) or the web vitals library in field reports can highlight slow interactions. In the lab, you can simulate user actions in DevTools (Recorder or manually) to find slow callbacks. Once identified, follow the principles above to shrink those delays.

By reducing JavaScript execution times, splitting large tasks, and yielding control to the browser more often, you make the site feel snappier. In practice, even a small reduction in the 75th-percentile INP can greatly improve perceived responsiveness, especially on mobile devices with slower CPUs.

Optimizing Cumulative Layout Shift (CLS)

Cumulative Layout Shift quantifies how much page elements unexpectedly move around. To achieve a good CLS (≤0.1), you must eliminate or reserve space for elements that load asynchronously. Common causes are images/videos without size, ads or iframes inserted late, and web fonts causing text reflow. Key techniques include:

Illustration: a before/after comparison of layout stability. In this Lighthouse screenshot, an image’s layout shift was fixed by specifying its dimensions. The before CLS was 0.363 (unacceptable); after adding width/height, it dropped to 0.1 (good). Always reserving space for content dramatically reduces CLS.

• Always specify dimensions (width/height or aspect-ratio): For every <img>, <video>, or <iframe>, include the width and height attributes (or CSS aspect-ratio) to reserve the correct space before the resource loads. Modern browsers use these attributes to compute a default aspect ratio and allocate the layout space upfront. For example: <img src=”photo.jpg” width=”800″ height=”600″ alt=”…”>. Even if you style the image to width:100%, the browser will maintain the aspect ratio so the page layout doesn’t jump when the image loads. In the example above, adding dimensions to images cut CLS from 0.363 to 0.100. Without dimensions, the browser initially reserves 0×0 space (causing the content to “jump” into place when loaded).
• Reserve space for late-loading content (ads, embeds, iframes): Dynamic content like ads, third-party widgets, or chat widgets can push other content around. To prevent this, pre-allocate an appropriate placeholder. For fixed-size content (like a known ad slot), set a min-height or aspect-ratio on the container. For responsive ads (unknown size), use CSS to maintain the aspect ratio of the most common size. Never collapse the space if no ad appears (collapsing to 0 causes as much shift as the content itself). For content without a fixed size, consider placing it lower on the page where shifts are less jarring. If you must insert banners or notifications at the top, either reserve space in advance (e.g., a hidden banner of that height) or show them as overlays (positioned layers) so other content isn’t moved.
• Avoid inserting content above existing content: For example, when loading more list items or new posts, append them below instead of prepending. If showing dynamic banners or popups, overlay them or ensure users expect the content (like after a click). If an update must happen, try to animate or indicate it so the shift isn’t so abrupt. The CLS metric will ignore shifts that happen within 500ms of user interaction, but it’s best not to rely on that – design the page so unexpected shifts don’t occur.
• Use transform animations for UI changes: If you animate UI elements (e.g., opening menus, dialogs, collapsible sections), use transform: translate or opacity transitions, which are compositor-only and don’t trigger layout changes. Animating properties like top, left, width, or triggering reflows (box-sizing, box-shadow) can cause layout shifts for other elements. CSS animations or JavaScript-driven animations favor transform and opacity. For example, sliding in a panel with transform: translateX() won’t affect the layout of the rest of the page.
• Optimize web font loading: Flash of unstyled (FOUT) or invisible text (FOIT) can cause shifts. Use a fallback font that is in the same category as the web font (e.g., sans-serif) to minimize size differences. You can also use font-display: optional or swap to avoid text being invisible or moving. With font-display: optional, the browser will use the fallback and only switch if the web font loads quickly enough, thus avoiding a late shift. Preload critical fonts so that text renders sooner and doesn’t require a reflow. Chrome also supports newer font metrics (size-adjust, etc.) to align fallback sizes to the final font.
• Ensure page is back/forward cache (bfcache) friendly: This doesn’t directly fix initial CLS, but it means if a user navigates back to your page, they’ll see it exactly as they left it (no reload shifts). Chrome’s bfcache can dramatically reduce perceived CLS in navigation, so avoid things (like certain unload handlers) that disable it.

In practice, fixing CLS often means combing through your page for any images, ads, or scripts that inject content without size. Browser DevTools (Lighthouse or the Performance timeline) can show layout shift “gaps” and the elements causing them. As a quick test, look at the Lighthouse CLS audit or use the Web Vitals live metrics. The easiest fixes are usually adding missing width/height attributes to images and videos and ensuring that any late content (ads, images in infinite scroll, etc.) has reserved space. Even small improvements in CLS can remove jarring jumps and make the site feel much more polished.

Tools for Measuring Core Web Vitals

Web developers and SEO professionals have a variety of tools to measure and monitor Core Web Vitals, often using a combination of lab tests and real-user data:

• PageSpeed Insights (PSI): Enter a URL on PageSpeed Insights to run a Lighthouse analysis and fetch CrUX field data. The report shows your LCP, INP, and CLS scores and indicates whether they are Good, Needs improvement, or Poor. It provides diagnostic suggestions for improving each metric. Note that as of May 2024, PSI uses Lighthouse 12.0 for its lab tests, so it includes the latest performance audits.
• Lighthouse (Chrome DevTools or CLI): Run Lighthouse in Chrome’s DevTools (Audits panel) or via the command-line. It simulates page load under throttled conditions and reports performance metrics including LCP, TBT (Total Blocking Time), and more. Lighthouse can also perform “Lighthouse in Chrome” while you manually interact with the page (using the Lighthouse User Flows feature) to catch dynamic CLS. While Lighthouse’s reports focus on performance scores, you can filter its opportunities and diagnostics to target LCP, CLS, or INP specifically.
• Chrome DevTools Performance Panel (Live Metrics): In recent Chrome versions, the Performance tab has a “Live” view that displays Core Web Vitals as the page loads. After recording a trace, the Summary tab will list LCP, INP, CLS, and other metrics. This is an interactive way to see exactly when LCP occurred on the timeline and what caused it. Since early 2025, Chrome merged the Web Vitals extension into DevTools, so you no longer need an extra plugin to see these metrics in-browser.
• Chrome UX Report (CrUX): The official dataset of field metrics from Chrome users. You can query CrUX via BigQuery or use the CrUX API to get aggregated LCP/CLS/INP data (for your site or samples of the web). Google’s CrUX release notes announced that FID has been removed from CrUX as of 2024, and INP is now used. By exploring CrUX data (e.g. via Google’s CrUX BigQuery sandbox, or the CrUX API), you can see how many origins pass Core Web Vitals or how your site’s metrics differ by country or device.
• Google Search Console – Core Web Vitals Report: If you have a registered property, Search Console will show a Core Web Vitals report that groups pages by “Good/Need Improvement/Poor” for each metric. It’s based on CrUX data for your indexed URLs. Use it to spot systematic issues (e.g., “Pages with poor CLS”). The report includes trend charts and details for specific URL groups. It is a handy way for SEOs or marketing teams to monitor CWV health of the site over time.
• Web Vitals JavaScript Library: For custom analytics or RUM, Google’s web-vitals JS library can programmatically measure LCP, INP, CLS, etc., in users’ browsers and send the results to your analytics platform. Renault’s case study describes using this library to push data into Google Analytics for correlation with conversions. Many third-party performance monitoring tools (Cloudflare Web Analytics, New Relic Browser, Sentry, etc.) now report Core Web Vitals as well.
• Performance Monitoring Tools: Many third-party tools specifically track Core Web Vitals, such as Calibre, SpeedCurve, or PageSpeed monitoring services. These can continuously audit your site’s URLs and alert if vitals degrade.
• Chrome Web Vitals Extension: This was a Chrome browser extension that displayed CWV in the toolbar. It has been officially sunsetted in 2025, but you may still encounter references to it. Users should now rely on DevTools or PSI for measuring vitals.

Each tool has its strengths. Lab tools (Lighthouse, DevTools) are good for diagnosing and simulation. CrUX-based tools (PSI field data, Search Console, CrUX API) show how real users experience your site. A recommended workflow is; measure field data (to confirm you have a problem), reproduce the issue in the lab (DevTools/Lighthouse), fix it, then verify in production RUM again. For example, PSI will show your 28-day field LCP score (from CrUX) alongside the simulated one, highlighting any discrepancy.

Case Studies: Real-World Results from Core Web Vitals Optimization

Numerous companies have reported significant business improvements after improving Core Web Vitals. Here are a few illustrative examples from published case studies:

• Vodafone (Italy) – After optimizing server-side rendering, images, and CSS, Vodafone reduced its LCP by 31%. This seemingly modest speedup resulted in an 8% increase in sales, a 15% higher lead-to-visit rate, and an 11% better cart-to-visit rate.
• iCook (Taiwan) – By converting critical recipe images to static (server-side) images and setting explicit heights, iCook lowered its CLS by ~15%. The result was a 10% rise in ad revenue from more stable page layouts, with minimal impact on ad fill rate. This shows that even visual stability alone can boost user engagement.
• Tokopedia (Indonesia) – This large e-commerce company tackled render-blocking scripts and optimized homepage assets, achieving a 55% faster LCP. Users then spent 23% more time on the site on average, indicating higher engagement.
• RedBus (India) – RedBus made extensive improvements to all Core Web Vitals. The outcome was a dramatic jump in conversion rate (mobile conversions roughly doubled to triple) and a top-spot increase in SEO rankings for key pages. In other words, better CWV helped RedBus convert and attract more customers.
• Yahoo! Japan (Japan) – After fixing a site-wide CLS issue, Yahoo Japan saw a 98% reduction in “poor” pages and a 15% uplift in page views per session.
• AliExpress (China) – By slashing CLS by 10× (through reserves for images/ads) and halving LCP (via image optimization), AliExpress achieved a 15% reduction in bounce rate.
• NDTV (India) – Analyzing 55% faster LCP on their news site, NDTV reported a 50% lower bounce rate on pages with improved LCP.
• Renault (France) – As mentioned earlier, Renault’s in-depth analysis found that each second reduction in LCP translated to 13% more conversions and a 14-point drop in bounce.
• Swappie (Finland) – This e-commerce site saw a 42% increase in mobile revenue after focusing on Core Web Vitals, along with a 23% faster average load time.

These examples (among many) demonstrate a consistent theme: speed and stability drive engagement and conversions. In SEO terms, sites with good Core Web Vitals are also more likely to see improvements in search visibility over time. As one list of case studies humorously puts it, everyone from large media sites (e.g., BBC lost 10% users per extra second of load) to e-commerce brands (e.g., Renault, Flipkart) has found that performance fixes pay back in revenue.

In practice, you can use these stories to convince stakeholders that optimizing LCP, CLS, and INP isn’t just a technical exercise – it can yield double-digit gains in key metrics like conversions or pageviews. In fact, Google’s own Chrome team highlights that improving a relatively small fraction of Core Web Vitals (like fixing just LCP or CLS on critical pages) has shown measurable lifts in site metrics.

Conclusion

Core Web Vitals – LCP, INP, and CLS – are now industry-standard metrics for web performance that directly reflect user experience. They have become critical for SEO and business success, as Google uses them in search ranking, and users react positively to fast, smooth sites. Staying up-to-date on the 2024 changes (FID→INP, Lighthouse 12+, Chrome DevTools updates) ensures you’re measuring the right things.

Optimizing each metric requires specific techniques: load the largest content quickly for LCP, keep the main thread free for INP, and stabilize the layout for CLS. This involves both high-level architectural choices (like SSR and CDNs) and low-level coding best practices (like specifying image sizes and yielding in JavaScript). Use the available tools (PageSpeed Insights, Lighthouse, Search Console, RUM) to measure, diagnose, and monitor your improvements. And remember to correlate these technical metrics with business KPIs using analytics or A/B tests.

By relentlessly pursuing Core Web Vitals improvements, development teams, and marketers can make pages feel faster and more reliable. The payoff is happier users, better SEO positions, and, ultimately, stronger business outcomes. In the competitive web landscape of 2024–2025, Core Web Vitals are a key part of a holistic performance strategy – and the data shows they matter.

Sources: Official Google documentation and developer blogs (e.g., Google Search Central, web.dev, Chrome DevTools blog) and reputable case studies on Core Web Vitals