Core Web Vitals are a set of specific factors that Google considers crucial for measuring the overall user experience of a website. These factors focus on three key aspects: loading, interactivity, and visual stability.

1. Largest Contentful Paint (LCP): This metric measures the time it takes for the largest element on a webpage to become visible to the user. It indicates how quickly the main content of a page loads. A good LCP score is typically under 2.5 seconds. For example, if a webpage has an image as the largest element, LCP measures the time it takes for that image to fully load.

2. First Input Delay (FID): FID measures the time from when a user interacts with a webpage (e.g., clicks a button) to when the browser responds to that interaction. It quantifies the interactivity of a page. A good FID score is typically under 100 milliseconds. For instance, if a user clicks on a button and there is a noticeable delay before the webpage responds, it indicates a poor FID score.

3. Cumulative Layout Shift (CLS): CLS measures the visual stability of a webpage by calculating the unexpected layout shifts that occur during the page's lifecycle. It quantifies how much content unexpectedly moves around, causing a poor user experience. A good CLS score is typically under 0.1. For example, if a webpage loads with text and images shifting around as other resources load, it indicates a high CLS score.

These Core Web Vitals are essential because they directly impact user satisfaction and engagement. Websites that prioritize optimizing these metrics tend to offer a better user experience, resulting in improved search engine rankings and higher user retention.

References:

• https://web.dev/vitals/
• https://developers.google.com/web/fundamentals/performance