Low impact · weight 4 · worth up to 2.5 points of the total score
Without a usable Cache-Control header, browsers and CDNs re-fetch the page on every visit, so returning visitors pay the full load cost again for content that did not change.
Send Cache-Control with a max-age suited to how often the page really changes, even if that is only a few minutes.
Check a page for this, and the other 41 checks at once
HTML document weight
This is the HTML document alone, before images and scripts. A multi-megabyte document usually means the whole page was rendered server-side into one response, and every visitor pays for it on every load.
Lighthouse performance score
Google's own composite of loading, interactivity, and visual stability, measured on a simulated mid-range phone. This is the number PageSpeed Insights puts at the top of its report.
Largest Contentful Paint
LCP is the moment the biggest element in the viewport finishes rendering, which is when a visitor feels the page has arrived. Google's threshold for good is 2.5 seconds.
Cumulative Layout Shift
CLS measures content jumping around after it appears. It is why a visitor taps the wrong button when an ad or a late-loading image pushes the page down under their finger.
