Learn about the three Core Web Vitals: LCP, FID & CLS

Learn about the three Core Web Vitals: LCP, FID & CLS • Yoast

Edwin Toonen

Edwin is a strategic content specialist. Before joining Yoast, he spent years honing his skill at The Netherlands’ leading web design magazine.

Some time ago, Google caused quite a stir by announcing a new ranking factor for 2021: page experience. User experience has always been an essential part of building the best site out there, but now, it will play an even bigger role in helping you build awesome sites for your customers. All this is powered by new metrics, with at the center: the Core Web Vitals. Time to meet LCP, FID, and CLS!

Page Experience will roll out in May, 2021, Google announced.

The Google page experience update powered by Web Vitals

We’ve talked about this page experience update before, but we’d like to take another look at those Core Web Vitals. In general, site speed metrics tend to be hard to understand and confusing. Plus, they tend to change somewhat each time you test your site. You don’t always get the same scores. It’s easy to say that you have to look at some metrics hoping they turn green. 

Of all the possible metrics, Google now identifies three so-called Core Web Vitals. These are the focal point for Google in the coming year. Every year, Google might add or change these metrics as they evaluate them over a longer time. 

Core Web Vitals are the subset of Web Vitals that apply to all web pages, should be measured by all site owners, and will be surfaced across all Google tools. Each of the Core Web Vitals represents a distinct facet of the user experience, is measurable in the field, and reflects the real-world experience of a critical user-centric outcome.

web.dev/vitals/

The three pillars of page experience

For now, the three pillars of page experience are:

  • Loading performance (how fast does stuff appear on the screen?)
  • Responsiveness (how fast does the page react to user input?)
  • Visual stability (does stuff move around on the screen while loading?)

To measure these essential aspects of user experience, Google chose three corresponding metrics — aka the Core Web Vitals:

  • LCP, Largest Contentful Paint: This measures how long it takes for the largest piece of content to appear on the screen. This could be an image or a block of text. A good grade gives users the feeling that the site loads fast. A slow site can lead to frustration.
  • FIS, or First Input Delay: This measures how long it takes for the site to react to the first interaction. This could be a tap on a button, for instance. A good grade here gives the user a sense that a site is quick to react to input and, therefore, responsive. Slow, again, leads to frustration.
  • CLS, or Cumulative Layout Shift: This measures the visual stability of your site. In other words, does stuff move around on the

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This article was written by Edwin Toonen and originally published on SEO blog • Yoast.

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