What Are Core Web Vitals?

Core Web Vitals are a set of metrics Google uses to measure the user experience of a webpage — specifically how fast it loads, how responsive it is to user input, and how visually stable it is. There are currently three main metrics:

LCP — Largest Contentful Paint

LCP measures how long it takes for the largest visible element on the page to load. This is usually a hero image, a large heading, or a video thumbnail. Google wants LCP under 2.5 seconds. Between 2.5–4 seconds needs improvement. Over 4 seconds is considered poor.

LCP is the metric that most frequently fails on slower-loading websites. The biggest culprits are large uncompressed images, slow server response times, and render-blocking scripts.

INP — Interaction to Next Paint

INP replaced FID (First Input Delay) as of 2024. It measures the overall responsiveness of a page — how quickly the page responds to user interactions like button clicks, form inputs, and link taps. Google wants INP under 200 milliseconds.

Poor INP is usually caused by too much JavaScript running on the main thread, blocking the browser from responding to user input quickly.

CLS — Cumulative Layout Shift

CLS measures visual stability — how much the page layout shifts around as it loads. You’ve experienced bad CLS when you go to tap a button and suddenly it moves because an image or ad loaded above it. Google wants CLS under 0.1.

Common causes: images without defined width and height attributes, ads loading without reserved space, and fonts swapping in late and causing text to shift.

How to Check Your Core Web Vitals

The best tools for checking:

• Google Search Console: Check the Core Web Vitals report (under Experience). This shows real-user data from Chrome users — more meaningful than lab data.
• PageSpeed Insights: Enter any URL at pagespeed.web.dev for both lab and field data, plus specific recommendations.
• Chrome DevTools Lighthouse: Built into Chrome — right-click → Inspect → Lighthouse tab. Good for development testing.

What to Prioritise If Scores Are Poor

For LCP (slow loading):

• Compress and properly size all images (WebP format where possible)
• Add the fetchpriority="high" attribute to your hero image
• Use a fast hosting provider or CDN
• Reduce or defer non-essential JavaScript

For INP (poor responsiveness):

• Reduce third-party scripts (chat widgets, analytics, social embeds)
• Break up long JavaScript tasks
• Use code splitting to only load JS when needed

For CLS (layout shifts):

• Add explicit width and height attributes to all images
• Reserve space for ads and embeds
• Use font-display: optional or preload your fonts

Do Core Web Vitals Actually Affect Rankings?

Yes, but they’re not the most powerful ranking factor. They function more as a tiebreaker — if two pages are roughly equal on relevance and authority, the one with better page experience is likely to rank higher. For most businesses, technical SEO fundamentals (indexing, content quality, internal links) are more impactful than chasing perfect Core Web Vitals scores.

That said, genuinely poor scores (especially on mobile) do have a real-world impact. A page that takes 8 seconds to load on mobile will lose visitors regardless of its ranking — and that bounce rate feeds back into how Google perceives the page.

Aim for “Good” scores rather than perfection. Fix the obvious performance issues, then focus your energy on content and relevance.