Google grades every page on the web against three specific measurements, collectively called Core Web Vitals. They're not abstract engineering metrics — they map directly to what a visitor actually experiences, and Google uses them as a genuine ranking signal. Here's what each one means in plain terms.

LCP — Largest Contentful Paint

LCP measures how long it takes for the biggest visible element — usually a hero image or headline — to render on screen. It's Google's proxy for "does this page feel like it's loading, or does it feel broken." Under 2.5 seconds is good; past 4 seconds, most visitors have already started to lose patience.

INP — Interaction to Next Paint

INP measures the delay between a visitor tapping a button or link and the page actually responding. This one replaced an older metric called FID in 2024 because it captures responsiveness across the whole visit, not just the first click. A sluggish INP is often what's behind the feeling that a site is "laggy" even after it's finished loading.

CLS — Cumulative Layout Shift

CLS measures visual stability — how much content jumps around while the page loads. You've felt this: you go to tap a button and an ad loads above it at the last second, so you tap the wrong thing. That's a CLS problem, and it's one of the most common reasons a site "feels cheap" even if it's fast.

Check your own score for free. Run any URL through PageSpeed Insights (pagespeed.web.dev) and it will report all three metrics using real visitor data where available, plus a lab test. It's the same tool Google uses internally, so there's no guesswork about what "good" means for your specific site.

What actually moves the needle

Most sites don't need a rebuild to improve these numbers — they need a handful of specific fixes:

  • Compress and correctly size images — this is the single biggest lever for LCP on most sites
  • Reserve space for images and ads before they load, so nothing shifts (fixes CLS)
  • Defer non-essential JavaScript so the main thread is free to respond to clicks (fixes INP)
  • Use a CDN so content loads from a server physically close to the visitor

None of this is exotic — it's mostly discipline applied consistently, which is exactly why so few sites actually do it well. It's also why a Lighthouse score in the high 90s, like the one we hold ourselves to on every static build, is a genuinely meaningful thing to point to rather than a vanity number.