Core Web Vitals are performance metrics used by Google to measure the speed, responsiveness and visual stability of a website.
If your site is failing Core Web Vitals assessments, it can affect both user experience and search visibility. Many websites struggle with these metrics because performance issues often originate from underlying technical factors such as scripts, images, server configuration or inefficient code.
This guide explains what Core Web Vitals measure, why websites fail them, and what steps can help improve performance.
What Core Web Vitals Measure
Core Web Vitals focus on three key metrics that influence how users experience a webpage.
Largest Contentful Paint (LCP)
Measures how long it takes for the main content of a page to become visible. A slow LCP indicates that users must wait too long before the page appears to load.
Interaction to Next Paint (INP)
Measures how responsive a page is when users interact with it, such as clicking buttons or links.
Cumulative Layout Shift (CLS)
Measures visual stability and tracks whether page elements move unexpectedly during loading.
Together, these metrics help determine whether a page provides a fast and stable user experience.
How to Check Your Core Web Vitals
You can check Core Web Vitals performance using several tools.
Google Search Console
Search Console provides a Core Web Vitals report showing which pages on your site are classified as Poor, Needs Improvement, or Good.
PageSpeed Insights analyses a specific page and provides detailed recommendations for improving performance.
Lighthouse
The Lighthouse performance audit in Chrome DevTools can also help identify issues affecting page speed and user experience.
Common Causes of Core Web Vitals Problems
Many websites fail Core Web Vitals due to technical issues within the site’s code or configuration.
Large or Unoptimised Images
Large image files can significantly delay page loading times and increase Largest Contentful Paint.
Images should be compressed and served in modern formats such as WebP where possible.
Excessive JavaScript
Heavy JavaScript files can delay page rendering and slow down interaction responsiveness.
Scripts from analytics tools, marketing platforms and plugins often contribute to performance issues.
Render-Blocking Resources
CSS or JavaScript that must load before the page can render may delay the appearance of content.
Optimising these resources can help improve loading performance.
Poor Caching Configuration
Caching helps browsers store resources locally so pages load faster on repeat visits.
If caching is not configured correctly, the server may need to regenerate resources for every page load.
Slow Server Response TimeServer performance can affect how quickly a page begins loading.
Hosting infrastructure, database queries and inefficient code can all influence response times.
Plugin Conflicts in WordPress
WordPress websites often use multiple plugins, which can introduce performance issues if they load excessive scripts or conflict with each other.
Identifying problematic plugins is often a key step in resolving performance problems.
Improving Core Web Vitals
Improving Core Web Vitals typically involves a combination of technical improvements, including:
- optimising images and media
- reducing unnecessary JavaScript
- improving caching and resource delivery
- removing unused scripts or plugins
- optimising server performance
- reviewing theme and plugin behaviour
Because performance issues often have multiple causes, diagnosing the underlying problem is usually the most important step.
Need Help Improving Core Web Vitals?
If your website is failing Core Web Vitals assessments and the cause is unclear, the issue may require deeper technical investigation.
MarkIT Space provides Core Web Vitals optimisation and technical SEO diagnostics to identify and resolve performance issues affecting website speed and user experience.