--- title: Core Web Vitals: What it is and how it works url: https://blog.krasovskiy.team/en/core-web-vitals-what-it-is-and-how-it-works/ date: 2025-09-30 lang: en source: blog.krasovskiy.team --- # Core Web Vitals: What it is and how it works # What are Core Web Vitals: The Complete Guide to Improving Site Performance Core Web Vitals are a set of key metrics from Google that measure the actual [user experience](https://blog.krasovskiy.team/en/digital-marketing-what-it-is-and-how-it-works/) on web pages. These web greetings have become critical to SEO and overall [site performance](https://blog.krasovskiy.team/en/the-main-requirements-for-the-mobile-version-of-the-site/) since May 2021, when Google officially included them in the ranking factors. Understanding what Core Web Vitals are and how they affect your site will greatly improve your user experience and search engine rankings. ![Core Web Vitals Analysis](https://img.b2bpic.net/premium-photo/looping-neon-glow-effect-magnifying-glass-icon-search-website-black-background_737078-3292.jpg) ## Introduction to Core Web Vitals: Why It Matters to Your Site The entry of Core Web Vitals into the world of web development was a real revolution in website quality assessment. Google created these metrics to objectively measure the real user experience when interacting with web pages. Unlike traditional speed indicators, web vitalas focus on three critical aspects: content loading speed, interactivity and visual stability. The definition of Core Web Vitals includes three main metrics: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). Each of these metrics is responsible for a specific aspect of the user experience. LCP measures the loading time of the largest visible element on the page, FID measures the delay between the user's first interaction with the page and the browser's response, and CLS monitors the visual stability of the content during loading. ## Basics of Core Web Vitals: Three Key Metrics The Core Web Vitals fundamentals are based on a deep understanding of how Core Web Vitals work in real-world environments. Each metric has its own threshold values ​​that determine the quality of the user experience: "Good", "Needs improvement" and "Poor". To achieve optimal results, it is important to understand what affects each metric. ### Largest Contentful Paint (LCP) LCP measures the time it takes to display the largest content element in the viewport. It can be an image, a video, or a large text block. Core Web Vitals explains that LCP is a critical measure of user perception of loading speed. To improve LCP, it is recommended to optimize images, use CDN, minify CSS and JavaScript, and ensure fast server response. ### First Input Delay (FID) FID measures the time from the user's first interaction with the page to the moment when the browser can process that interaction. This definition of Core Web Vitals helps you understand how quickly a site responds to user actions. A high FID is often caused by heavy JavaScript blocking the main browser thread. To optimize FID, you should separate long JavaScript tasks, use web workers, and defer non-critical JavaScript. ### Cumulative Layout Shift (CLS) CLS evaluates the visual stability of a page by measuring unexpected displacements of elements during loading. What are Core Web Vitals in the context of CLS? This is an indicator of how stable your page layout is. A high CLS can lead to accidental clicks on the wrong elements. To minimize CLS, always specify dimensions for images and videos, avoid inserting content on top of existing content, and use animations sparingly. ## How Core Web Vitals Work: Technical Aspects and Measurements Understanding how Core Web Vitals work on a technical level allows you to optimize your site more effectively. Google collects web welcome data from real users through the Chrome User Experience Report (CrUX). This data is based on the 75th percentile of all page loads, which provides a representative estimate of the experience of most users. There are several tools for measuring Core Web Vitals: PageSpeed Insights, Lighthouse, Chrome DevTools, and Search Console. Each tool provides different types of data—field (from real users) and lab (simulated tests). Field data reflects real-world user experience, while lab data is useful for diagnosing and testing improvements before implementation. It is important to understand that web welcome may vary depending on the user's device, network and geographic location. Therefore, optimization should take into account different usage scenarios. Mobile devices often perform worse due to limited resources and slower networks, so special attention should be paid to mobile optimization. > Core Web Vitals have become an integral part of modern web development, defining the quality standards of user experience. Understanding and optimizing these metrics is not just a technical necessity, but an investment in the success of your online presence. Sites with good web welcome scores not only rank better in search, but also provide a better user experience, leading to higher conversions and audience loyalty. Start with basic optimizations and gradually improve each metric, regularly monitoring progress through available Google tools.