Insights · Field note · Growth and AI visibility
Core Web Vitals on a phone in a parking lot
The visitor who matters is on a phone, on a weak connection, deciding whether to call. The page has about a second.
Core Web Vitals are Google’s three measures of page experience: Largest Contentful Paint, with a good threshold of 2.5 seconds or less; Interaction to Next Paint, 200 milliseconds or less; and Cumulative Layout Shift, 0.1 or less, each at the 75th percentile of real visits. They matter for rankings modestly and for trust substantially. A prospective patient or client on a phone in a parking lot does not wait for a slow page or forgive a button that moves under their thumb. Vitals in the green on mobile is a property of the build, not a periodic rescue.
In detail
What the evidence shows.
The three measures
Largest Contentful Paint is when the main content appears. Interaction to Next Paint is how quickly the page responds to a tap. Cumulative Layout Shift is how much the page moves unexpectedly. Google publishes the thresholds and reports field data in Search Console, which is the number that counts; lab tools explain the causes.
Why mobile is the test
Field data is dominated by mobile visits on variable connections. A page that is fast on an office desktop and slow on a phone fails the measure and the visitor. We set budgets and measure on mobile settings against real pages, not a test page.
What usually breaks them
Oversized images without declared dimensions. Render-blocking stylesheets and scripts. Slow fonts. Third-party tags nobody justified. Content injected above what the visitor is reading. Most are fixed in the design system and the build so that every page inherits the fix.
Keeping them fixed
A performance budget per page type and a build check that fails pages exceeding it. Measurement in the monthly report. On a static, edge-delivered site with disciplined scripts, green Vitals are the normal state. The triage checklist covers diagnosis; see performance engineering and the glossary entry for Core Web Vitals.
Sources
Primary references.
By David Selakovic · Published 2026-10-16 · Revised 2026-10-16 · Reviewed every 180 days