FCP (First Contentful Paint)

This is the first moment the browser renders anything from the DOM onto the screen — before it, the page is entirely blank; under 1.8s is good and beyond 3s is poor.

This metric is the user's first psychological point of contact with your site, showing that the browser has started doing its job. If there's a wide gap between this metric and LCP, it means the page shows the user a light initial paint very early on, but its real, valuable content arrives late — a sign of a heavy resource sitting in the critical rendering path that's worth investigating.

From a business angle, if this time stretches out, the user feels the site has frozen or isn't loading at all; so they close the page before seeing even the smallest piece of content, and bounce rate climbs. Keeping this metric in check makes sure user-acquisition budgets aren't wasted, and that visitors get a sign of life from the site in those first seconds, keeping their engagement with the product alive.