Determines how quickly the largest and the most important content on the site loads.

Reports the render time of the largest image or text block visible within the viewport relative to when the page first started loading.

Sites should strive to have the Largest Contentful Paint of 2.5 seconds or less.

Determines how quickly a user can start interacting with the site (click, scroll, etc.).

FID measures the time from when a user first interacts with a page (i.e. when they click a link, tap on a button, or use a custom, JavaScript-powered control) to the time when the browser is actually able to begin processing event handlers in response to that interaction.

Sites should strive to have a First Input Delay of 100 milliseconds or less.

Determines how much the layout is shifted and if it's stable or not.

A layout shift occurs any time a visible element changes its position from one rendered frame to the next. CLS is a measure of the largest burst of layout shift scores for every unexpected layout shift that occurs during the entire lifespan of a page.

Sites should strive to have a CLS score of 0.1 or less.

• Largest Contentful Paint (LCP)
• First Input Delay (FID)
• Cumulative Layout Shift (CLS)