Core Web Vitals are Google's attempt to measure how a page actually feels to a real user: does it load quickly, respond promptly, and stay visually stable? They influence search ranking, but the better reason to care is that they correlate with the things you want anyway — engagement, conversion, and trust. Here's the checklist we work through, grouped by the three metrics that matter.

LCP — Largest Contentful Paint (loading)

LCP measures how long until the biggest thing in the viewport — usually a hero image or headline — appears. Users read it as "how fast did the page load." The wins are almost always the same:

  • Optimize the hero. Serve modern image formats, size them correctly, and preload the LCP image so the browser fetches it early.
  • Cut server response time. Cache aggressively, use a CDN, and get to first byte fast; you can't paint before the HTML arrives.
  • Unblock rendering. Trim and defer render-blocking CSS and JavaScript so the browser can paint sooner.
  • Self-host or preconnect fonts so text doesn't wait on a third-party round trip.

INP — Interaction to Next Paint (responsiveness)

INP replaced First Input Delay as the responsiveness metric, and it's stricter: it measures the delay across all interactions, not just the first. It punishes heavy JavaScript that blocks the main thread while the user is trying to click or type. Our approach:

  • Ship less JavaScript. The fastest code is the code you don't send. Audit bundles and drop what isn't needed.
  • Break up long tasks. Split heavy work so the main thread stays free to respond to input, and move non-urgent work off the critical path.
  • Defer and lazy-load anything not needed for the first interaction, including below-the-fold components.
  • Be honest about framework cost. Rich client-side apps can struggle here; server-rendering and hydration strategy matter.

CLS — Cumulative Layout Shift (visual stability)

CLS measures how much the page jumps around as it loads — the maddening moment a button moves just as you tap it. It's usually the cheapest of the three to fix:

  • Always set dimensions (width/height or aspect-ratio) on images, video, and embeds so the browser reserves space.
  • Reserve space for dynamic content like ads, banners, and async widgets instead of letting them shove content down.
  • Avoid inserting content above existing content after load, and use font-loading strategies that don't cause big text reflows.

Measure real users, not just the lab

Lab tools like Lighthouse are great for diagnosis, but Core Web Vitals are ultimately about field data — real visitors on real devices and networks. We rely on field measurement (via the Chrome UX Report and real-user monitoring) to know what's actually happening, because a page that scores well on a fast laptop can still be painful on a mid-range phone.

Build it in, don't bolt it on

The teams that struggle with Web Vitals usually treat performance as a cleanup task before launch. The teams that pass treat it as a constraint they design within from the start — a performance budget, sensible defaults, and monitoring that catches regressions before users do. Fast isn't a one-time fix; it's a habit. And it's one of the few investments that helps your users and your search ranking at the same time.