Core Web Vitals: Why site speed directly affects your business today

What are Core Web Vitals?

Core Web Vitals are a set of metrics that Google has defined to measure the quality of user experience on websites.

In other words, it's not just about whether the site loads, but how quickly and how steadily the user can start using it.

Google has introduced these metrics as part of its SEO criteria, which means site performance today directly affects search rankings.

Core Web Vitals focus on three key aspects of user experience:

• speed of loading main content
• speed of site response to interaction
• layout stability during loading

If a site is slow, elements "jump" around the screen, or the user has to wait to click a button, it negatively affects both users and Google rankings.

Three key Core Web Vitals metrics

1. Largest contentful paint (LCP)

LCP measures how quickly the main content of the page loads.

This is usually:

• hero image
• large heading
• video poster
• or the largest visual element in the viewport

Google recommends that LCP be under 2.5 seconds.

If LCP is slow, the user sees an empty page or skeleton layout and feels like the site is "stuck".

The most common causes of poor LCP are:

• oversized images or video content
• slow server response (TTFB)
• blocking CSS or JavaScript
• unoptimized fonts

In practice, hero sections with large images or video often represent the biggest optimization challenge.

2. Interaction to next paint (INP)

INP measures how quickly the site responds when the user takes an action.

For example:

• clicking a button
• opening a menu
• filling out a form
• navigating between sections

If you click a button and nothing happens for half a second or longer, that's a bad signal for user experience.

Google recommends that INP be under 200 milliseconds.

The most common reasons for poor INP are:

• too much JavaScript
• heavy front-end frameworks
• poor event handler optimization
• main thread blocking in the browser

In other words, even if the site loads quickly, it can feel slow if interactions are delayed.

3. Cumulative layout shift (CLS)

CLS measures how much the page layout shifts during loading.

You've surely experienced wanting to click a button, when an ad or image loads and everything shifts.

Result: you click the wrong thing.

Google considers a good CLS to be below 0.1.

The most common causes of layout shift are:

• images without defined dimensions
• fonts that change text size after loading
• late insertion of banners or iframes
• ads and embed content

A stable layout is important because it directly affects trust and the professional impression of the site.

Why are Core Web Vitals important?

There are three main reasons.

1. SEO

Google has clearly confirmed that Core Web Vitals affect search rankings.

It's not the only factor, but when two sites are similar in content, the faster site has the advantage.

This is especially important for mobile devices where competition is fierce.

2. Conversions

Speed directly affects business results.

Research shows that:

• a slow site increases bounce rate
• users leave the page faster
• conversion rate drops

Even a 1 second difference in loading time can significantly affect sales or number of leads.

3. Professional impression

A fast site sends a clear message:

• the company is modern
• technology is well set up
• user experience is a priority

A slow and unstable site often creates the opposite impression.

How are Core Web Vitals measured?

There are several tools that most developers use.

The best known are:

Google PageSpeed Insights
Analyzes performance and provides optimization recommendations.

Lighthouse
Developer tool built into Chrome that enables detailed site auditing.

Chrome DevTools Performance panel
Used for deeper analysis of performance and rendering.

Google Search Console
Shows real user data (field data) from the Chrome browser.

It's important to understand the difference between:

• lab data (test in controlled conditions)
• field data (real users on real devices and networks)

Google uses field data for ranking.

How to improve Core Web Vitals?

Optimization usually involves a combination of several techniques.

Image and video optimization

Large media files are often the biggest problem.

Solutions include:

• modern formats like WebP or AVIF
• responsive images
• lazy loading
• optimized video poster instead of autoplay video

Font optimization

Fonts can significantly affect page rendering.

The most common techniques are:

• preload key fonts
• reduce number of font variations
• use font-display: swap

Reducing JavaScript

Too much JS code blocks the browser.

That's why we often use:

• code splitting
• defer and async scripts
• removing unnecessary libraries

Server and CDN optimization

Performance doesn't depend only on the frontend.

Important factors are also:

• fast hosting
• CDN network
• server caching
• TTFB time optimization

The reality of performance optimization

It's important to say one thing: performance optimization is a process, not a one-time action.

Every new feature can affect site speed:

• new plugin
• marketing scripts
• video content
• third-party tools

That's why serious projects regularly do performance audits and balance between functionality and speed.

Conclusion

Core Web Vitals have become the standard of modern web development.

They don't just measure the technical speed of a site, but the quality of the experience the user has while using the site.

A faster and more stable site means:

• better SEO positions
• more conversions
• more satisfied users
• a more professional digital identity

If you're developing a new site or improving an existing one, performance optimization shouldn't be the last thing on the list, but part of the development strategy itself.

Want to check your site's performance?

Contact me and we'll do a quick performance audit of your site, with concrete recommendations on what can be improved and what effect it can have on SEO and user experience.