Core Web Vitals are three measurements Google uses to judge the experience of loading a page. Google takes them from real visits, not from a lab test, which is why a site can score well in a tool and badly in the field.
The three measurements
- Largest Contentful Paint. How long until the main content appears. Under two and a half seconds is the target.
- Interaction to Next Paint. How quickly the page responds when somebody taps or clicks.
- Cumulative Layout Shift. Whether things jump around while loading, which is what makes people tap the wrong thing.
How much do they affect ranking?
They are one signal among many, and rarely the reason a page is not ranking. The larger effect is commercial: a slow page loses visitors before they read anything.
Fixing Core Web Vitals issues
Typically, we test Core Web Vitals before and after every website build, because a fast build that fails these measurements later is a common cause of lost traffic.
For example, Google’s own Core Web Vitals documentation explains exactly how the scoring works in the field.
Specifically, images and third-party scripts cause most of the failures we see, more often than the code developers write themselves. Similarly, a site can pass on desktop and fail badly on mobile, so both need testing separately. Notably, fixing the worst-performing pages first usually moves the site-wide score fastest.
However, a beautiful design can still fail these measurements if nobody ever optimized the underlying code for real devices. Instead, treat performance testing as part of every launch checklist, not a task somebody remembers only after visitors complain.
Notably, the tools that report these scores update their methodology occasionally, so a page that passed last year is worth checking again rather than assuming it still holds up.
For example, a page that scores well on a fast office connection can still fail badly for a visitor on a slow mobile signal.
