What You’ll Learn

• A short story about my experience
• Core Web Vitals: CLS, LCP, FID
• Practical tips for developers improving SEO

My Journey into Core Web Vitals & SEO

Last year, I worked on a website where my main goal was to improve its SEO. The challenge? There was no SEO expert on the team. That meant I had to learn everything myself—reading, experimenting, and breaking things along the way.

After a year of trial and error, I realized that optimizing SEO isn't just about metadata and keywords. It's deeply technical, and Core Web Vitals play a crucial role in search rankings.

Here’s what I wish I knew when I started.

Understanding Core Web Vitals

Google defines Core Web Vitals as three key performance metrics that directly impact user experience and search rankings:

• Cumulative Layout Shift (CLS) – Measures visual stability. A low CLS means fewer unexpected shifts in page content.
• Largest Contentful Paint (LCP) – Measures loading performance. The time it takes for the largest visible element to load.
• First Input Delay (FID) – Measures interactivity. The time it takes for the page to respond to the first user action. (Note: FID is being replaced by Interaction to Next Paint (INP) in 2024.)

Lessons Learned: Tips for Developers Improving SEO

1. Lighthouse and Other Audit Tools Are Almost Useless Alone

Tools like Lighthouse and PageSpeed Insights give a single snapshot of performance. The problem? They test on one device, one connection, one specific moment. Real users have different experiences.

Use field data (Chrome UX Report, PageSpeed Web Vitals API) to measure real-world performance.

2. Performance Optimizations Can Break SEO

Improving performance often means lazy loading images, deferring scripts, or reducing DOM complexity. But be careful:

• Lazy loading can hide content from search engines.
• Aggressive JavaScript optimizations can delay rendering important elements.
• Over-optimizing for performance might break SEO-critical features (like structured data).

Always test SEO impact after making performance changes.

3. Improving One Metric Often Improves Others

Web performance is interconnected.

• A faster LCP usually improves FID.
• A stable CLS means a better user experience, reducing bounce rates.
• Optimizing rendering paths often improves multiple metrics at once.

4. You Won’t See Results Immediately

SEO is a long game. Google needs time to crawl, index, and evaluate performance changes. Some improvements can take weeks or even months to reflect in rankings.

5. There’s No Universal Fix—Always Measure Impact

There’s no "one-size-fits-all" solution.

• Make a change → Measure impact → Adjust
• Use PageSpeed Insights, WebPageTest, and Real User Monitoring (RUM)
• Track before and after scores in Google Search Console

6. Mobile Performance is More Important Than Desktop

Google prioritizes mobile-first indexing. If your site isn’t desktop-only, mobile performance matters way more.

• Test on real mobile devices, not just emulators.
• Measure Core Web Vitals with slow 4G or throttled networks to simulate real-world users.

7. Testing CLS? Scroll & Interact!

Cumulative Layout Shift (CLS) isn’t just about page load—it also happens when users scroll or interact.

• When testing with WebPageTest or similar tools, scroll to the end and trigger some interactions.
• A page might look fine on load but shift when new elements appear late.

8. The Most Important Numbers Are in PageSpeed Insights

Forget chasing perfect Lighthouse scores. The real impact is in Google's PageSpeed Insights and Search Console Core Web Vitals reports—because that’s what Google actually uses for ranking.

Final Thoughts

SEO isn't just about keywords and backlinks—it’s deeply tied to performance. If you’re working on improving SEO, start with Core Web Vitals, measure real-world impact, and be patient.

Want to dive deeper? Check out:

• Web.dev Core Web Vitals Guide
• Google Search Central: Core Web Vitals & SEO