Core Web Vitals, explained in plain English.

What are the three Core Web Vitals?

Thresholds as published by Google. A page passes when at least 75% of real visits meet the “good” level for each metric.

What is LCP and what slows it down?

Largest Contentful Paint is the moment the page looks loaded — the main image, video poster or block of text is on screen. Common causes of a slow LCP:

• Slow server response — cheap or overloaded hosting, no page caching.
• A huge hero image that hasn’t been resized or compressed, or is lazy-loaded when it should load first.
• Render-blocking CSS and JavaScript that must download before anything appears.
• Web fonts that delay text from showing.

What is INP and why does it feel laggy?

Interaction to Next Paint replaced the older First Input Delay metric in 2024. It looks at the delay between a visitor’s tap or click and the next visual update — across the whole visit, not just the first interaction. A poor INP is the “I tapped the menu and nothing happened” feeling.

The usual cause is too much JavaScript running on the browser’s main thread: chat widgets, trackers, sliders, page-builder scripts and third-party tags all compete. Fixes include removing scripts you don’t need, delaying non-essential ones until after the page loads, and breaking up long tasks in custom code.

What is CLS and how do you stop the page jumping?

Cumulative Layout Shift measures unexpected movement — the button that slides away just as you tap it. It usually comes from:

• Images and videos without a set width and height.
• Ads, embeds or cookie banners that push content down after it appears.
• Fonts swapping in and changing the size of text.
• Content injected above what’s already on screen.

The fix is to reserve space: give media fixed dimensions, give banners and embeds a fixed slot, and add new content below the visitor rather than above.

Why do my scores differ between tools?

Field data (real users)

• Collected from real Chrome visitors over the past 28 days
• Shown in Search Console and at the top of PageSpeed Insights
• What Google uses for page experience
• Slow to change after a fix

Lab data (a single test)

• One simulated load on a set device and connection
• The Lighthouse score in PageSpeed Insights
• Great for finding causes and testing fixes
• Varies from run to run

How do you check your Core Web Vitals?

1. Open PageSpeed Insights and test your homepage and your most important page, on mobile.
2. Look first at the real-user section at the top. If your site doesn’t have enough traffic, you’ll only see lab data — use it as a guide.
3. In Google Search Console, open the Core Web Vitals report to see which groups of pages pass or fail.
4. After fixing something, give the field data a few weeks to catch up before judging the result.

What usually fixes Core Web Vitals?

1. Hosting & caching — A fast server and page caching help LCP most.
2. Images — Resize, compress, set dimensions, load the hero first.
3. Scripts — Remove or delay third-party and unused JavaScript.
4. Reserve space — Fixed slots for media, banners and embeds.
5. Re-measure — Lab test now, field data in a few weeks.