Supported by Chrome, the Web Vitals is a Google initiative to provide unified guidance for metrics that are crucial for delivering the best user experience for websites and webapps.
Core Web Vitals¶
Largest Contentful Paint (LCP)¶
Measures page loading performance. Google suggests that LCP should be below 2500 milliseconds, which means that to provide a good user experience, the largest contentful paint should occur within 2.5 seconds of when the page first starts loading.
First Input Delay (FID)¶
Measures interactivity of the web application. Google suggests that to provide good user experience, pages should have a first input delay of less than 100 milliseconds. Please note that FID is not measured in Sematext Synthetics.
Cumulative Layout Shift (CLS)¶
Measures visual stability of the web page. To provide a good user experience Google suggests that the pages should maintain a cumulative layout shift of less than 0.1.
Other Web Vitals Metrics¶
In addition to the Core Web Vitals, both Sematext Experience and Sematext Synthetics support the supplemental Web Vitals metrics often used to help with diagnostics of specific issues on the web page. Those metrics are:
Time to First Byte (TTFB)¶
Measures the time it takes the server to send a response for the request. It is suggested that to provide a great user experience the time to the first byte should be below 600 milliseconds. Higher values may discourage users from interacting with the site and are usually cause application performance issues such as long page loads.
First Contentful Paint (FCP)¶
Measures the time from when the page starts loading to when any part of the page's content is rendered on the screen. Unlike the largest contentful paint, the first contentful paint tells the site owner when the initial page element is rendered on the user screen. It is said that the first contentful paint should be kept below 1000 milliseconds to achieve a good user experience.
Web Vitals in Experience¶
The information about Web Vitals in Experience is present as a set of numeric components and charts.
The main Web Vitals panel shows the 75th percentile for both the Core and Other Web Vitals:
In addition to the panel showing the 75th percentile, the information is presented in an easy to read graphs that visualize the data for the selected time period: