Core Web Vitals explained: LCP, CLS and interaction speed

Core Web Vitals are three measurements of how fast, stable and responsive a page feels, and each has a pass line you can check.

Core Web Vitals are three measurements Google publishes to describe how a page feels to a real person. They matter for leads because a slow or jumpy page loses visitors before they read a word. They are also a small part of what search engines weigh, so a fast page helps twice. See the glossary entry for the short version.

Largest Contentful Paint (LCP)#

LCP is how long the biggest visible item, usually a hero image or a main headline, takes to appear. Google counts 2.5 seconds or less as good, and over 4 seconds as poor. The usual causes of a slow LCP are an oversized image, a slow server and scripts that block the page from drawing. More on LCP.

Cumulative Layout Shift (CLS)#

CLS adds up how much the page jumps while it loads. You have felt it: you go to tap a button and an advert loads above it, pushing it down. A score of 0.1 or less is good, and over 0.25 is poor. The usual causes are images with no set width and height, late-loading banners and web fonts that swap in. More on CLS.

Interaction speed (INP)#

Interaction to Next Paint measures the delay between a tap, click or key press and the page visibly responding. Google counts 200 milliseconds or less as good and over 500 as poor. Heavy scripts that keep the browser busy are the usual cause: the page looks ready but ignores you.

How to check your own pages#

1. Open Google's free PageSpeed Insights, paste a page address and run it.
2. Read the top section, labelled as real-user data. It comes from actual visitors over the last 28 days. If it is missing, the page has too little traffic for Google to report on.
3. Read the lab section below it for the specific items slowing the page, such as an image to shrink or a script to defer.
4. In Google Search Console, the Core Web Vitals report groups your pages into good, needs improvement and poor, so you can fix a whole group at once.

Common mistakes#

• Testing only the home page. Your service and landing pages are where leads are won, and they often score worse.
• Trusting one lab run. Scores vary between runs, so run it three times or lean on the real-user data.
• Chasing a perfect 100. Passing all three lines is the goal; the last few points rarely change results.
• Checking desktop only. Most visitors arrive on a phone, on a slower connection.

Next, see how to speed up a slow page. In PageSoar, broken links and page speed shows where your own pages stand.