Core Web Vitals - LCP, FID and CLS
Web Vitals is an initiative by Google to provide unified guidance for quality signals that are essential to delivering a great user experience on the web. The core of this initiative, Core Web Vitals, represents a subset of metrics that apply to all web pages and should be measured by all site owners. These metrics capture the user experience in loading performance, interactivity, and visual stability of the page. Understanding and improving these factors can significantly enhance user satisfaction.
Core Web Vitals
Core Web Vitals consist of three main metrics:
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Largest Contentful Paint (LCP): Measures loading performance. To provide a good user experience, LCP should occur within 2.5 seconds of when the page first starts loading. LCP marks the point in the page load timeline when the page's main content has likely loaded—a key factor in how users perceive the speed of your page.
- Example: If a user visits a news site and the main article text or the largest image headlines appear on the screen within 2.5 seconds, the site is considered to have a good LCP score.
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First Input Delay (FID): Measures interactivity. To provide a good user experience, pages should have an FID of 100 milliseconds or less. FID measures the time from when a user first interacts with your site (i.e., when they click a link, tap on a button, or use a custom, JavaScript-powered control) to the time when the browser is able to respond to that interaction.
- Example: When a user clicks a login button, if the browser processes the interaction and starts the login process within 100 milliseconds, the page meets the recommended FID criteria.
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Cumulative Layout Shift (CLS): Measures visual stability. To provide a good user experience, pages should maintain a CLS of 0.1. or less. CLS measures the sum total of all individual layout shift scores for every unexpected layout shift that occurs during the entire lifespan of the page. A layout shift happens anytime a visible element changes its position from one rendered frame to the next.
- Example: If a user is reading an article and an ad suddenly inserts itself above the content, pushing it down, this results in a poor CLS score. A good CLS score would mean the page’s content does not shift during loading, except in response to user interactions.
Why Web Vitals Matter
Web Vitals are crucial for understanding and improving the user experience. A poor user experience can lead to higher bounce rates, lower conversion rates, and can negatively impact a site's ranking in search engines. By focusing on these metrics, developers and site owners can target key areas that matter most to users and improve the overall health of their sites.
How to Measure Web Vitals
Google provides several tools to measure and report on these metrics, including:
- Chrome User Experience Report: Provides real-world user experience insights for popular destinations on the web.
- PageSpeed Insights: Analyzes the content of a web page, then generates suggestions to make that page faster, including Web Vitals metrics.
- Lighthouse: An open-source, automated tool for improving the quality of web pages. It has audits for performance, accessibility, progressive web apps, and more.
Improving these vital metrics can lead to a better user experience, potentially leading to increased engagement and conversions. By making Web Vitals a part of the development process, site owners can ensure their sites are built with performance and user experience front and center.