I first heard the phrase "Core Web Vitals" in a panic.
A fellow website owner messaged me saying his traffic had dropped significantly after a Google update, and someone told him it was because of his Core Web Vitals scores. He had no idea what that meant. Neither did I at the time.
I went and checked my own scores immediately. What I found made me stop everything else I was working on and spend the next two days understanding and fixing this specific part of my website's performance.
Core Web Vitals turned out to be one of the most important — and most misunderstood — parts of modern SEO. Once I understood what they measured and why Google introduced them, everything about page experience and user-focused SEO clicked into place for me.
This guide will explain exactly what Core Web Vitals are, what each one measures, why Google uses them as a ranking factor, and how to check and improve your own scores for free.
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What Are Core Web Vitals?
Core Web Vitals are a set of three specific measurements Google uses to evaluate the real-world experience of visiting a webpage. They are not about content quality or keywords. They are purely about how a page feels to use — how fast it loads, how stable it is, and how quickly it responds to interaction.
Google first introduced Core Web Vitals on May 28, 2020, as part of its Page Experience initiative. After giving website owners more than a year to prepare, Google officially began using Core Web Vitals as ranking signals on June 15, 2021, with the full rollout completed by August 2021. Core Web Vitals measure three critical aspects of user experience: loading performance (LCP), interactivity (FID), and visual stability (CLS). This was a significant moment because it meant Google was no longer just asking, "Is this content relevant?" It was also asking, "Does this page actually feel good to use?"
The three measurements are Largest Contentful Paint, First Input Delay, and Cumulative Layout Shift. Each one measures a different aspect of the user experience. Together, they give Google a picture of whether your page delivers a smooth, fast, stable experience or a frustrating, slow, jumpy one.
Read the related article: What Are Core Web Vitals and Why Do They Matter for Your SEO Rankings?
Largest Contentful Paint — How Fast Your Page Loads
Largest Contentful Paint, usually shortened to LCP, measures how long it takes for the largest visible element on your page to fully load. This is usually your hero image, your main headline, or a large block of text at the top of the page.
LCP is important because it represents the moment when a visitor feels the page has actually arrived. The page might have started loading immediately, but if the biggest visible element takes five seconds to appear, the visitor experience feels slow — even if other smaller elements loaded faster.
Google's target for a good LCP score is 2.5 seconds or less. Between 2.5 and 4 seconds needs improvement. Anything over 4 seconds is considered poor.
The most common causes of a slow LCP are large uncompressed images, slow server response times, and render-blocking resources — the same issues we covered in the page speed article. Compressing your hero image is usually the single most effective fix for a poor LCP score.
First Input Delay — How Fast Your Page Responds
First Input Delay, shortened to FID, measures how long it takes for your page to respond when a visitor first interacts with it — clicking a button, tapping a link, or selecting from a menu.
Imagine clicking a button on a website and nothing happening for three seconds. You click again. Still nothing. Then suddenly it registers. That frustrating experience is exactly what a high First Input Delay feels like.
FID happens because the browser is busy processing JavaScript and other scripts when the visitor tries to interact. The browser cannot respond to the click until it finishes what it is already doing.
Google's target for a good FID score is less than 100 milliseconds — fast enough that the response feels instant. Between 100 and 300 milliseconds needs improvement. Over 300 milliseconds is poor.
The main fix for a high FID is reducing the amount of JavaScript running on your pages, deferring scripts that are not needed for the initial page load, and breaking up long tasks that keep the browser busy for extended periods.
Note that Google has recently replaced FID with a new measurement called Interaction to Next Paint — INP — which measures responsiveness more broadly across the entire page visit rather than just the first interaction. The principle is the same: your page should respond to visitor interactions quickly.
Cumulative Layout Shift — How Stable Your Page Is
Cumulative Layout Shift, shortened to CLS, measures how much your page layout unexpectedly moves around while it is loading.
You have almost certainly experienced this. You start reading an article on your phone, and suddenly an image loads above the text and pushes everything down. Your finger, which was about to tap a link, ends up tapping an advertisement instead. That sudden jump is a layout shift, and it is one of the most frustrating experiences on the web.
CLS measures the total amount of unexpected layout movement on a page during loading. A score of 0.1 or less is considered good. Between 0.1 and 0.25 needs improvement. Over 0.25 is poor.
The most common causes of layout shift are images without defined dimensions, advertisements that load and push content around, and web fonts that swap in late and cause text to reflow.
The fixes are straightforward. Always define the width and height of every image in your HTML so the browser reserves the correct space before the image loads. Set fixed dimensions for advertisement slots so they do not push content when they fill. Use font-display settings that prevent invisible text during font loading.
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Why Google Uses Core Web Vitals as a Ranking Factor
Understanding why Google cares about these measurements helps you understand how seriously to take them.
Google's entire business depends on people trusting its search results. When someone searches for something and clicks a result, Google wants that experience to be good. If the page loads slowly, jumps around, and does not respond to clicks, the visitor blames Google for sending them there — even if the content was exactly what they were looking for.
By rewarding pages that score well on Core Web Vitals and quietly pushing down pages that score poorly, Google is protecting the quality of every experience it sends people to. It is aligning its ranking signals with what visitors actually feel.
This is important for website owners because it means technical performance is now directly connected to search visibility. A website with great content but poor Core Web Vitals will lose rankings to a website with equally good content and better Core Web Vitals scores.
How to Check Your Core Web Vitals
Checking your Core Web Vitals is free and takes less than a minute.
Go to Auditest — auditest.online
Run a free audit on your website. The report includes your Core Web Vitals scores — showing your LCP, FID, INP, and CLS measurements alongside clear guidance on what each score means and what is causing any issues found.
The report tells you specifically which elements on your page are affecting each score. You do not need to guess what to fix. The audit points directly at the problem.
Pro Tip: Check your Core Web Vitals on mobile separately from desktop. Google primarily uses mobile scores for ranking purposes. A page that scores well on desktop can still have poor mobile Core Web Vitals due to slower connection speeds and different rendering behaviour on phones. Your Auditest report covers both.
How to Improve Your Core Web Vitals Scores
Once your audit report identifies the specific issues, here are the most effective fixes for each measurement.
To improve LCP: Compress and resize your largest images. Use modern image formats like WebP. Ensure your server responds quickly. Remove or defer render-blocking scripts and stylesheets that delay the main content from loading.
To improve FID or INP, reduce the amount of JavaScript running on your pages. Defer scripts that are not needed immediately. Break up long JavaScript tasks into smaller pieces. Remove unused third-party scripts — analytics tools, chat widgets, and social share buttons all add JavaScript weight.
To improve CLS: Add explicit width and height attributes to every image. Reserve fixed space for ads and embeds before they load. Avoid inserting content above existing content after the page has started loading. Choose web fonts carefully and use font-display settings to prevent text from jumping when fonts load.
The Fanal Point
Core Web Vitals are Google's way of measuring whether your website actually feels good to use. Poor scores mean poor rankings, regardless of how good your content is. Good scores give your pages a meaningful advantage over competitors who have ignored this part of their SEO.
The three measurements — LCP for loading speed, FID or INP for responsiveness, and CLS for visual stability — together tell Google whether a visitor landing on your page will have a smooth experience or a frustrating one.
Check your Core Web Vitals scores right now for free at auditest.online. See exactly where your pages stand, identify what is pulling your scores down, and start making the improvements that will protect and improve your search rankings.
Your visitors deserve a fast, stable, responsive experience. And Google is now making sure they get it — by ranking the websites that deliver it above the ones that do not.
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About the Author
Kester Terna is an SEO specialist and founder of Auditest, where he helps website owners identify technical SEO issues, improve search visibility, and grow organic traffic.