Core Web Vitals are performance metrics that Google uses as ranking signals. Poor scores can hurt your search visibility. Good scores contribute to better rankings.
More importantly, they measure what users actually experience: how fast pages load, how responsive they feel, and whether layouts stay stable.
The three metrics
Largest Contentful Paint (LCP)
LCP measures how long it takes for the main content to appear. It measures when the largest image or text block becomes visible.
What users experience: waiting for the page to show them something useful.
Good score: under 2.5 seconds. Poor score: over 4 seconds.
Common causes of poor LCP:
Slow server response time
Large unoptimised images
Render-blocking JavaScript or CSS
Client-side rendering that delays content display
Interaction to Next Paint (INP)
INP measures how quickly the page responds to user interaction. It tracks the delay between clicking or tapping and seeing a visual response.
What users experience: clicking a button and waiting for something to happen.
Good score: under 200 milliseconds. Poor score: over 500 milliseconds.
Common causes of poor INP:
Heavy JavaScript that blocks the main thread
Event handlers that perform expensive operations
Large DOM size that slows rendering
Third-party scripts that interfere with responsiveness
Cumulative Layout Shift (CLS)
CLS measures visual stability. It quantifies how much the page layout shifts unexpectedly during loading.
What users experience: clicking a link just as an ad loads above it, accidentally clicking the ad instead.
Good score: under 0.1. Poor score: over 0.25.
Common causes of poor CLS:
Images without width and height attributes
Ads or embeds that load late and push content down
Web fonts that cause text to reflow when they load
Dynamically injected content above existing content
How to check your scores
Google provides several tools:
PageSpeed Insights - shows both lab data and real user data
Search Console - Core Web Vitals report shows issues across your site
Chrome DevTools - Lighthouse tab for detailed diagnostics
Lab data tells you what tests found. Field data tells you what real users experienced. Field data matters more for rankings but requires enough traffic to collect.
What you can actually do
For LCP
Optimise and properly size images
Use a content delivery network
Enable caching for static resources
Preload critical resources
Ensure adequate server response time
For INP
Minimise JavaScript execution time
Break up long tasks into smaller chunks
Remove unused JavaScript
Defer non-critical third-party scripts
For CLS
Always include width and height on images and videos
Reserve space for ads and embeds
Use font-display: swap for web fonts
Avoid inserting content above existing content
Perspective
Core Web Vitals are one factor among many for search ranking. A site with mediocre scores but excellent content can still rank well. A site with perfect scores but poor content will not. Performance monitoring should be part of ongoing website maintenance to catch degradation early.
Focus on Core Web Vitals when:
Your scores are poor enough to affect user experience
You are competing in a space where competitors have better scores
You have already addressed other SEO fundamentals
Do not obsess over perfect scores at the expense of other priorities.
