Core Web Vitals: complete guide
Understand and improve LCP, FID, CLS. Essential metrics for performance and SEO.
Core Web Vitals are performance metrics defined by Google to measure the real‑world experience of users on your site.
They directly influence SEO and user satisfaction.
In this guide, we’ll look at the three main metrics and how to improve them.
The three Core Web Vitals
- LCP (Largest Contentful Paint) – how fast the main content appears
- FID / INP (First Input Delay / Interaction to Next Paint) – how quickly the page reacts to interactions
- CLS (Cumulative Layout Shift) – how stable the layout is while loading
You can measure them in tools like PageSpeed Insights, Lighthouse or the Chrome UX Report.
Why they matter
Core Web Vitals are not just a technical obsession:
- Faster loading = less frustration and more conversions
- Smooth interactions = more trust in your brand
- Stable layout = fewer accidental clicks and better usability
Google uses them as ranking signals, alongside many other factors.
They are particularly important on mobile, where network conditions are more variable.
Practical tips to improve Core Web Vitals
Improving LCP
- Optimise and compress hero images
- Use modern formats (WebP, AVIF)
- Avoid blocking scripts in the '<head>' section
- Use server‑side rendering or static generation where appropriate
Improving INP (interactivity)
- Avoid heavy, blocking JavaScript on initial load
- Split bundles and lazy‑load non‑critical components
- Minimise expensive computations during user interactions
Improving CLS (layout stability)
- Always reserve space for images and embeds with width/height or aspect‑ratio
- Avoid inserting content above existing content after load
- Be careful with dynamic fonts and external widgets
In my projects built with Next.js, I pay particular attention to these metrics from the very start of the design and development process.
You can see the impact in my own portfolio website and other client projects.
Conclusion
Core Web Vitals are a concrete, measurable way to align technical work with business results.
Improving them is good for SEO, conversions and user satisfaction.
If you want help diagnosing and improving your Core Web Vitals, you can reach out through the contact section.