Core Web Vitals Definition & Meaning

What Are Core Web Vitals?

Core Web Vitals are a set of metrics used by Google to measure user experience based on actual user data. Core Web Vitals consist of Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS).

Largest Contentful Paint (LCP): This metric measures how fast the main content of a web page loads from the time the user initiates loading the page until the largest image or text block is rendered within the viewport. LCP scores often diminish when web pages load large JavaScript files that need to be parsed and executed on the browser’s main thread. 

First Input Delay (FID): This metric measures the time from when a user first interacts with your site by clicking a link or tapping a button to the time when the browser actually responds to that interaction. FID often happens when the main browser thread is busy doing something so it doesn’t respond to the user.

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Cumulative Layout Shift (CLS): This metric measures the distance a web page unexpectedly shifts during the rendering process. CLS is most commonly caused by content like images and ads being injected into the page by late-running Javascript or not specifying exact width and height attributes for containers.

If a web page doesn’t have a passing score for any of the Core Web Vitals, then steps should be taken to fix it. Google uses Core Web Vitals as part of its ranking algorithm systems.

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