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Core Web Vitals Checker

Checks how users of mobile and desktop devices experience your website

What is Core Web Vitals Checker?

Core Web Vitals Checker is a free tool that checks how users of mobile and desktop devices experience your website, which is referred to as Core Web Vitals.

The Core Web Vitals Checker provides analysis on four major site performance factors (Largest Contentful Paint (LCP), Total Blocking Time (TBT), Cumulative Layout Shift (CLS), and First Input Delay (FID)) using data that is collected directly from the Google Chrome browser.

What are Core Web Vitals?

core web vitals

The Core Web Vitals are a collection of metrics that Google uses to evaluate the quality of a website. Largest contentful paint, first input delay, and cumulative layout shift are the three components that make up Core Web Vitals, which are all related to page speed and user experience.

Largest Contentful Paint (LCP)

LCP measure provides data on how long it took to render the biggest image or text block within the viewport from the moment the page loaded. LCP should happen within 2.5 seconds of when the website initially starts loading in order to give users a good user experience.

First Input Delay (FID)

FID is the amount of time it takes for a browser to begin processing event handlers once a user interacts with a page (by clicking a link, tapping a button). Websites need to load in less than 100 milliseconds to provide users a good experience.

Cumulative Layout Shift (CLS)

When a page has several unexpected layout shifts during its lifetime, the CLS is the highest number of total scores for those shifts. Pages should strive for a CLS of 0.1 or below to give a good user experience.

Total Blocking Time (TBT)

TBT evaluates how long it takes for a website to respond to interaction from the user, such as a mouse click, touch, or keypress. Pages should have a TBT of 200 milliseconds or lower to provide users a good experience.

Lighthouse and other page-loading simulators do not provide a realistic enough user experience to accurately assess FID (there is no user input). Total Blocking Time (TBT), on the other hand, can be measured in the lab and serves as a reliable stand-in for FID. Changes that boost performance in the lab should also boost it in the field, and vice versa for TBT and FID.