Core Web Vitals – Essential Metrics for a Healthy Site

What is Google Core Web Vitals

Google’s mission is to provide the best experience for users of its search engine.

Core Web Vital provides unified guidance for quality signals that are essential to delivering a great user experience on the web.

Core Web Vitals are the subset of Web Vitals that apply to all site pages, should be measured by all webmaster/site owners, and soon will be surfaced across all Google tools that measure webpage performance.

The metrics that makeup Core Web Vitals will evolve over time. The current Core Web Vitals set for 2020 focuses on three aspects of user experience.

– Loading
– Interactivity
– Visual stability

Search Signals for Page Experience - Core Web Vitals

In Google’s own words

The page experience signal measures aspects of how users perceive the experience of interacting with a web page. Optimizing for these factors makes the web more delightful for users across all web browsers and surfaces, and helps sites evolve towards user expectations on mobile. We believe this will contribute to business success on the web as users grow more engaged and can transact with less friction.

Google Core Principles of Search

  • Focus on the user
  • Most relevant with highest quality information
  • Algorithmic approach
  • Rigorously test every change

What is Largest Contentful Paint (LCP)

LCP measures the loading performance of a web page.

To provide good user experience, LCP should occur within 2.5 seconds of when the page first starts loading.

Largest-Contentful-Paint-LCP
Largest Contentful Paint (LCP)

Common causes of a poor LCP:


What is First Input Delay (FID)

First Input Delay (FID) measures interactivity.

To provide good user experience, Google recommends, pages should have an FID of less than 100 milliseconds.

First Input Delay (FID)
First Input Delay (FID)

Common causes of a poor FID

The main cause of a poor First Input Delay (FID) is heavy JavaScript execution. Optimizing, how JavaScript compiles, parses, and executes on your webpage will directly reduce FID.

To improve JavaScript execution time:


What is Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) measures visual stability.

To provide good user experience, Google recommends, Pages should maintain a CLS of less than 0.1

Cumulative Layout Shift (CLS)
Cumulative Layout Shift (CLS)

Common causes of a poor CLS

The most common causes of a poor CLS are:

  • Images without dimensions
  • Ads, embeds, and iframes without dimensions
  • Web Fonts causing FOIT/FOUT
  • Actions waiting for a network response before updating DOM
  • Dynamically injected content

Why use Core Web Vitals

Longer page load times have a severe effect on bounce rates.

Google announced Core Web Vitals will become a ranking factor in 2021. SEO managers & Developers have several months to worry about.

There are many tools available such as Google Page Speed Insights to measure and report on performance.  With Core Web Vitals, Google aims to simplify the landscape and help sites focus on the metrics that matter most.

In conclusion

Core Web Vitals ensures the page provides a great user experience, focusing on the aspects of loading, interactivity, and visual stability.

Google wants quality pages that load quickly on its search engine.

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