A year ago, Google announced that Core Web Vitals will form part of the search algorithm beginning in what will now be June 2021, along with other known page experience signals. In addition to this announcement, Google stated that they would be rolling out a test to provide a visual indicator in search engine results pages to highlight pages that provide a great experience.

CORE WEB VITALS
Core Web Vitals are a set of metrics related to speed, responsiveness, and visual stability, and they help website owners measure user experience on the web.
These metrics are based on things like:
- Loading performance (How fast do content, graphics, etc. appear on the web page?)
- Visual stability (How fast does it take for the web page to be interactive?)
- Responsiveness (How fast does it take for the web page to be stable?)
To measure these aspects of the user experience, Google chose three corresponding metrics known as Core Web Vitals:
LARGEST CONTENTFUL PAINT
This metric measures how long it takes for the largest image or text block to appear on the screen. This is different from the First Contentful Paint, a metric that concentrates on the first element that’s loaded rather than the biggest one. A high score gives users the feeling that the website loads fast
FIRST INPUT DELAY
The First Input Delay calculates how long it takes for the website to be ready for the first interaction. The First Input Delay focuses on the time between clicks, scrolls, or keyboard input and the processing of those interactions. A high score here gives the user a sense that a website is fast to react to input and is responsive.