If you have a website, you have probably heard the term "Core Web Vitals" mentioned somewhere — in an email from your developer, a Google update announcement, or a warning in your analytics dashboard. But what are they, and do you actually need to care?

The short answer: Yes, but not because you need to become a performance engineer. You just need to know whether your website is passing or failing — and what to do if it is not.

What Google's Core Web Vitals measure

Core Web Vitals are a set of three real-world performance metrics that Google uses to measure how visitors actually experience your website. They are not lab tests — they are based on data from real people visiting your site.

Largest Contentful Paint (LCP) — loading speed

LCP measures how long the main content on a page takes to appear. "Main content" means the biggest visible element — usually a hero image, heading, or video.

Good: 2.5 seconds or faster
Needs improvement: Between 2.5 and 4 seconds
Poor: Slower than 4 seconds

Why it matters: If your pages take too long to show their main content, visitors are more likely to leave before the page finishes loading. Google also considers slow LCP a ranking signal.

Interaction to Next Paint (INP) — responsiveness

INP measures how quickly your page responds when someone clicks, taps, or types. This replaced First Input Delay (FID) in 2024.

Good: 200 milliseconds or faster
Needs improvement: Between 200 and 500 ms
Poor: Slower than 500 ms

Why it matters: A slow-feeling website frustrates visitors. If a button takes half a second to respond after being tapped, the experience feels sluggish — especially on mobile.

Cumulative Layout Shift (CLS) — visual stability

CLS measures unexpected movement of page content while it loads. You have experienced this when text jumps around because an image or ad loads late.

Good: Score of 0.1 or lower
Needs improvement: Between 0.1 and 0.25
Poor: Higher than 0.25

Why it matters: Layout shifts are annoying and can cause visitors to click the wrong thing, especially on mobile. If an advert loads and pushes content down just as someone was about to tap a link, they may accidentally click the ad instead.

Supporting metrics: FCP and TTFB

Alongside the three Core Web Vitals, two supporting metrics provide additional context:

First Contentful Paint (FCP): How long until anything at all appears on screen. Good = under 1.8 seconds.
Time to First Byte (TTFB): How long the server takes to respond. Good = under 800 ms.

These are useful for diagnosing why a metric is poor. For example, slow TTFB suggests a hosting or server issue; poor LCP combined with good TTFB suggests an image or resource problem.

How you can check your Core Web Vitals

You have several options, from simple to detailed:

Google Search Console: The "Core Web Vitals" report shows which pages are passing and failing, based on real-user data. This is free and requires no technical setup.
PageSpeed Insights: Enter any URL and get a lab-based score plus real-user data if available.
Web Vitals Collector: A weekly email report that tells you what changed, what matters, and what to do next — in plain English. No dashboards to check.

What passing looks like

Google's threshold for a passing website is that at least 75% of pages meet the "good" threshold for each metric. If your site passes all three, Google considers your Core Web Vitals healthy — and your search ranking is not negatively affected by performance.

If you are failing one or more metrics, the first step is understanding which pages and which devices are affected. Most issues are fixable with targeted changes — optimising images, removing unnecessary scripts, or upgrading hosting.

What matters most for small businesses

If you run a small business website, you do not need to obsess over every millisecond. What matters is:

Are your pages loading in a reasonable time? (LCP)
Does your site feel responsive? (INP)
Does content jump around? (CLS)

If all three are healthy, your site is in good shape — and a weekly report can give you the confidence that nothing has silently broken between developer updates.