Core Web Vitals (LCP, INP, CLS)
Also known as: Web Vitals, LCP, INP, CLS, page experience
Google's three user-experience measurements — how fast the main content appears (LCP), how quickly the page reacts to taps and clicks (INP), and how much it jumps around while loading (CLS).
In plain English
Picture walking into a shop. LCP is how long until you can actually see the shelves — not the sign on the door, the thing you came for. INP is how long the assistant takes to react when you ask something. CLS is the shelves sliding sideways just as you reach for a product, so you grab the wrong one. Google measures all three from real visitors' browsers and uses them as a ranking and AI-Overview eligibility signal.
The numbers are taken from real people (the Chrome User Experience Report), not from a lab, so a fast office connection tells you nothing — what matters is the slow phone on a train. A page that passes all three feels instant and stable; a page that fails one feels broken even when the content is good.
How to fix / set it up
- Run the Core Web Vitals checker to see the field numbers for the page and which metric fails.
- LCP: compress and size the hero image, preload it, serve it from a CDN; inline critical CSS; defer non-critical JavaScript.
- INP: break up long tasks, load third-party scripts after interaction or remove them, keep hydration small.
- CLS: give every image, video and ad slot explicit dimensions; reserve space for late content; use
font-display: optionalor size-adjusted fallbacks.
Core Web Vitals Checker →Speed Test →
The technical detail
Thresholds, measured at the 75th percentile of real-user visits: LCP ≤ 2.5 s, INP ≤ 200 ms, CLS ≤ 0.1. Field data comes from CrUX (28-day rolling window); lab tools like Lighthouse approximate it and are useful for diagnosis, not for the verdict.
Typical causes: LCP — slow TTFB, render-blocking CSS/JS, an unoptimised hero image, fonts that block text; INP — long JavaScript tasks on the main thread, heavy third-party tags, hydration of large client components; CLS — images and embeds without width/height, late-loading ads or banners, fonts that swap metrics.
FAQ
Lighthouse says 95 but the checker says I fail — why?
Lighthouse is a lab run on one fast machine. Core Web Vitals are judged on real visitors at the 75th percentile, including slow devices and networks. Trust the field data.
Do Core Web Vitals affect AI visibility?
Indirectly. Google uses page experience in ranking and its AI features draw on ordinary indexing; a page that fails vitals is crawled and ranked like any other, but it loses the tiebreaker and the user trust that earns citations.