Core Web Vitals in plain English: LCP, INP and CLS
Core Web Vitals are the three measurements Google uses to judge how a page feels to a real visitor. They are measured on real devices, by real users, which is why a site can feel fast on your office connection and still score poorly.
LCP: how fast the main thing appears
Largest Contentful Paint measures how long it takes for the biggest visible element, usually a hero image or headline, to show up. Google’s guidance is to aim for 2.5 seconds or less.
On WordPress sites the usual culprits are:
- An oversized hero image served in an old format
- Slow hosting, so the server takes a long time to respond at all
- Fonts and stylesheets that block the page from drawing
INP: how fast the page responds to you
Interaction to Next Paint measures the delay between a tap or click and the page visibly reacting. It replaced the older First Input Delay metric as a Core Web Vital in March 2024, and it is stricter, because it looks at interactions throughout the visit rather than only the first one. The target is 200 milliseconds or less.
Poor INP nearly always comes from too much JavaScript. Every extra plugin that loads its own scripts on every page adds to the queue the browser has to work through before it can respond.
CLS: whether things jump around
Cumulative Layout Shift measures how much the layout moves while loading. If you have ever gone to tap a button and an advert pushed it away, you have experienced bad CLS. The target is a score of 0.1 or less.
The fixes are unglamorous: give every image and embed explicit dimensions, reserve space for banners, and load fonts in a way that does not reflow the text.
Where to look first
Do not start by installing a performance plugin. Start by measuring. Google Search Console has a Core Web Vitals report built from real visitor data, and PageSpeed Insights will show the same field data for a single URL.
Measure with real-user data, fix the largest problem, then measure again.
In our experience most WordPress sites get the biggest improvement from three things: properly sized modern-format images, fewer plugins loading scripts site-wide, and better hosting. Everything else is fine-tuning.