Run a Core Web Vitals test with real-user Chrome UX Report data. Measure LCP, INP, and CLS on mobile and desktop, then compare current and historical results.
Core Web Vitals, decoded
Core Web Vitals are Google's metrics for loading performance, responsiveness, and visual stability. The current metrics are Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS).
LCP measures when the largest visible content renders. INP measures how quickly a page responds to user interactions, and CLS measures unexpected movement during a session. INP replaced First Input Delay (FID) as a Core Web Vital on March 12, 2024.
Largest Contentful Paint or LCP measures the loading performance of a Web Page. It measures how long it takes a Web Page to load the largest element in the viewport. This largest element is usually an image or a section of text.
Cumulative Layout Shift or CLS is a Web Vital that measures the visual stability of a Web Page. A layout shift is an unexpected shift of elements on the Web Page and it results in a poor user experience. CLS is the cumulative score of all layout shifts occurring on a Web Page during the entirety of the user's session.
Interaction to Next Paint or INP is a new Core Web Vital that has replaced FID. It also measures the responsiveness on a Web Page. INP is the time between the user-action and the painting of the next-frame in response to that action.
First Input Delay or FID measures the responsiveness on a Web Page. As the name suggests, it measures the delay between a user-action (such as a button click) to the time it takes for the browser to initiate the processing of event handles associated with that user-action. FID has been retired as a Core Web Vital.
The Lab Data is obtained when performing a Lab/synthetic test in controlled environments. This data presents the real-time performance metrics of a website.
Field Data is the real-world performance data of users who have visited the website in the past. Field Data is obtained using Chrome's User Experience (CrUX) Report.
Time To Interactive and Total Blocking Time are measured by Lab Tools while First Input Delay is only measured by Field Tools. First Contentful Paint, Largest Contentful Paint, Interaction to Next Paint, Cumulative Layout Shift, and Time to First Byte can be measured by both Lab and Field Tools.
While this Tool reports the Field Data, the SpeedVitals Website Speed Test and Google PageSpeed Insights report both the Lab Data and the Field Data.
SpeedVitals obtains the Field Data from Google's Chrome User Experience (CrUX) API. This is the same source used by PageSpeed Insights. Hence, the Field Data Reported by this Tool is same as the Field Data available on Google PageSpeed.
However, PageSpeed Insights only reports the last 28-Days Data while SpeedVitals also reports the last 28-Days data as well as the Historic Data up to 12 Months (Entire Website) and for up to 6 Months (A single URL).
From the SpeedVitals blog
