Core Web Vitals still matter — and agents are less patient than humans

Core Web Vitals — Google's user-experience metrics — are usually discussed in terms of rankings and bounce rates. But there's a second audience for your site's performance now: automated visitors. A crawler with a fetch budget or an agent completing a task under a timeout gives you far less grace than a curious human. Slow sites don't just rank worse; they fail machine visits outright.

The three metrics in plain English

• LCP (Largest Contentful Paint): how long until the main content is visible. Good is under 2.5 seconds.
• INP (Interaction to Next Paint): how quickly the page responds when someone interacts. Good is under 200 ms.
• CLS (Cumulative Layout Shift): how much the layout jumps around while loading. Good is under 0.1.

Lab data vs field data

PageSpeed Insights gives you lab data — a simulated load in controlled conditions. The Chrome UX Report (CrUX) gives you field data — what real Chrome users actually experienced over the last 28 days. Both matter: lab data for debugging, field data for truth. Our scanner reports both when available.

The fixes that usually move the needle

• Compress and properly size images — the single most common LCP killer.
• Set explicit width/height on images and embeds to stop layout shift.
• Cut unused JavaScript; ship less, defer the rest.
• Use a CDN and cache aggressively for static assets.
• Preload the one font and hero image that actually matter.

Perfection isn't the goal — passing the 'good' thresholds is. Beyond that, effort is better spent on structured data and content clarity, which is exactly why our readiness score weighs performance as one category among seven, not the whole story.