Core Web Vitals (CWV) Explained: Why Site Speed & UX Matter for SEO
Google wants to provide users with the best possible experience, and that includes sending them to websites that load quickly and are easy to interact with. That’s why Core Web Vitals (CWV) are an important part of Google’s Page Experience signals and remain a key consideration for SEO in 2025.
Understanding and optimising for these metrics is crucial for both user satisfaction and search visibility.
What Are the Core Web Vitals?
Core Web Vitals are a specific set of metrics Google uses to measure real-world user experience related to loading performance, interactivity, and visual stability. The current key metrics are:
- Largest Contentful Paint (LCP): Measures loading performance. It marks the point in the page load timeline when the largest image or text block visible within the viewport is likely to have rendered. A good LCP score (generally under 2.5 seconds) means users perceive the page as loading quickly.
- Interaction to Next Paint (INP): Measures interactivity or responsiveness. It assesses the latency of all user interactions (like clicks, taps, or key presses) made with a page, reporting the longest interaction duration. A low INP (generally under 200 milliseconds) indicates the page responds quickly to user input. (INP replaced First Input Delay (FID) as a core vital in March 2024).
- Cumulative Layout Shift (CLS): Measures visual stability. It quantifies how much unexpected shifting of visible page elements occurs during the entire lifespan of the page load. A low CLS score (generally under 0.1) means users don’t experience frustrating layout shifts where buttons move just as they try to click them.
Why Do Core Web Vitals Matter for SEO?
CWV are important for several reasons.
- User Experience: These metrics directly reflect aspects of user experience. Slow-loading, unresponsive, or unstable pages frustrate users, leading to higher bounce rates and lower engagement.
- Ranking Signal: Google uses Core Web Vitals as part of its Page Experience signals, which contribute to search rankings. While not the only factor, good CWV scores can give you an edge, particularly when competing against pages with otherwise similar content quality.
- Overall Site Health: Optimising for CWV often involves improving overall website performance and code efficiency, which benefits site health in numerous ways.
Common Causes of Poor CWV Scores & How to Improve Them
Optimising Core Web Vitals requires a technical approach.
- Slow LCP: Often caused by slow server response times, render-blocking JavaScript/CSS, or large, unoptimised images or videos. Solutions include upgrading hosting, optimising images (correct formats, compression, dimensions), deferring non-critical JavaScript, and minifying code.
- High INP: Frequently caused by excessive JavaScript execution taking up the browser’s main thread, preventing it from responding quickly to user input. Solutions involve breaking up long tasks, reducing JavaScript payload, optimising third-party scripts, and minimising main-thread work.
- High CLS: Usually caused by images or ads loading without defined dimensions, dynamically injected content shifting existing elements, or web fonts causing layout shifts as they load. Solutions include specifying size attributes for images/videos, reserving space for ads, and preloading critical fonts.
Measuring and Monitoring CWV
You can measure your Core Web Vitals using various tools.
- Google Search Console: The Core Web Vitals report shows aggregated field data (real user data) for your site.
- PageSpeed Insights: Provides both lab data (simulated load) and field data (if available) for specific URLs, along with optimisation suggestions.
- Chrome DevTools: Allows developers to measure CWV locally during development.
- Web Vitals Extension: A Chrome extension for measuring CWV in real-time.
Core Web Vitals are a critical link between technical performance and user satisfaction. By prioritising LCP, INP, and CLS, you create a better experience for your visitors and strengthen your site’s SEO foundation.
Axiom Flux provides technical SEO audits that include Core Web Vitals analysis and optimisation recommendations.
