What Is Core Web Vitals? Why It Is Important.

Introduction to Core Web Vitals

Core Web Vitals are basically three measures that check how fast a webpage loads, how interactive it is, and how stable it looks visually. They're super important for SEO because search engines use them to rank websites. If you improve these metrics, your site can climb higher in search results and give users a smoother experience.
Basically, Core Web Vitals are a few specific things that Google pays attention to when it's figuring out how good or bad your webpage is in terms of user experience. They're like a part of Google's grade for your webpage's overall experience.
Earlier, it was tough for web developers to figure out how fast the main stuff on a web page actually shows up for users. The usual ways we used to measure this, like the "load" or "DOM Content Loaded" events, aren't great because they don't match up exactly with what the user sees. And the newer fancy metrics, like "First Contentful Paint," only catch the very start of loading. So, if a page shows a splash screen or a loading symbol, that moment isn't super helpful to the user.
So, here are three Core Web Vitals metrics that help to enhance user experience.
What are the three Core Web Vitals:

  • Largest Contentful Paint (LCP): It shows how much time the biggest thing on a webpage takes to load. For a good experience, it's best if this happens in less than 2.5 seconds.
  • Cumulative Layout Shift (CLS): This measures how much a webpage's layout moves unexpectedly while loading. To keep things smooth, it's recommended to have a CLS of less than 0.1.
  • First Input Delay (FID): This one checks how quickly the webpage reacts when you do something for the first time, like clicking a button or tapping a link. It's better if this happens in less than 100 milliseconds for a smooth user experience.

And there's a new metric called Interaction to Next Paint (INP) that Google plans to use instead of FID starting from March 2024. For a fast and responsive experience, INP should be 200 milliseconds or less.

Why are Core Web Vitals important?

Google's making page experience a big deal for how they rank sites. They'll look at things like HTTPS, mobile-friendliness, no annoying pop-ups, and having a safe, malware-free site. Core Web Vitals, including LCP, will be a huge part of this scoring.

Core Web Vitals
Will a high page experience score get you to the top of Google?

Not exactly. Google considers around 200 things when ranking sites. Page experience is just one of them.

What's Google saying about ranking changes next year?

They're giving a heads-up that you've got time till next year to make your site's Core Web Vitals better.

So, how can you improve your Core Web Vitals score?

Let's focus on LCP, one of the three Core Web Vitals:

What is LCP?

LCP stands for Largest Contentful Paint. It's a user-centric performance metric that measures how long it takes for the largest content element in the viewport (like an image or a block of text) to become visible to the user when they're loading a webpage. Essentially, it gauges how quickly the main content of a page appears on the screen. A fast LCP is important for delivering a better user experience, indicating that the most important parts of a page load quickly for users.

What's a good LCP score?

Well, to make sure your website gives users a great experience, aim for a Largest Contentful Paint (LCP) of 2.5 seconds or faster. To check if you're hitting that goal for most visitors, focus on the 75th percentile of page loads on both mobile and desktop devices. That way, you'll have a good idea if your site's loading speed is meeting the mark for most users.
LCP is about how long it takes for a page to load for a user. It's different from other speed measurements because it's more about what users see and interact with, rather than technical stuff.

How can you check your LCP score?

Google's PageSpeed Insights or Website Checker can help.

Why should you look at LCP data in Google Search Console?

It gives you data about your whole site, unlike Page Speed Insights. You get a list of URLs that need work.

What's a good LCP speed?

Google says aiming for under 2.5 seconds for every page is great.

But why might a page have a slow LCP?

Pages with lots of big images or features might struggle. For instance, a page with many high-res images might take longer to load.

How can you make LCP better?

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There are some ways:
1. Remove unnecessary third-party scripts that slow your page.
2. Get a better web host for faster loading.
3. Remove lazy loading for images.
4. Remove big elements that slow things down.
5. Trim down your CSS to speed things up.

What Counts as the Largest Contentful Paint (LCP)?

Here's a breakdown of the details in simpler language:

  • Images & Videos: Any main images or videos on a webpage count towards LCP, like regular images (img), images within SVGs (image inside svg), and videos with a poster image.
  • Background Images: Images set as background through CSS (url()) also count if they're substantial content, not just decorative.
  • Text Blocks: Blocks of text or text-containing elements are considered if they're a significant part of the page.
    Special Cases:
  • For autoplay videos, the first frame shown counts as the LCP (since they play automatically without user interaction).
  • Animated image formats like GIFs are also considered from their first frame.

Filtering Out Unimportant Elements

  • Elements that users can't see (opacity 0), elements covering the entire screen (probably background), and low-information images are filtered out. These are considered non-contentful.
  • Browsers keep improving on these rules to match what users expect as the most meaningful content.

How Element Size is Determined?

  • For LCP, the visible part of an element within the view is considered. Parts outside the view or clipped aren't counted.
  • Images resized from their natural size report either their displayed size or their original size, whichever is smaller.
  • Text elements only count the size of the text itself, not any extra space around it like margins or borders.

When is the Largest Contentful Paint Identified?

  • Browsers mark the LCP as soon as they display the main contentful element. This might change as the page loads further.
  • If something bigger appears later or if a previously unseen element becomes the largest, the browser updates the LCP information.
  • However, elements not fully loaded (like images or fonts) or things added later might change what's considered the "largest".

Important Points to Note:

  • The browser stops updating the LCP once the user interacts with the page (by tapping, scrolling, etc.).
  • Analysis-wise, it's best to track the most recent LCP update for your analytics.
  • There's a delay in reporting LCP if the user opens the page in a background tab. Tools don't count this to reflect what users truly experience.

First Input Delay

Think about when you're on a website for the first time. That first experience matters a lot, right? It's like when you meet someone new - the first impression can determine if you'll stick around or leave.
On the internet, this first impression is about how fast things load and how easy it is to use the website. If a website takes too long to load or feels sluggish when you try to click on something, it's not a great experience.

How do we know there’s First Input Delay

To measure this, we use things like First Contentful Paint (FCP) to see how quickly a website shows content and First Input Delay (FID) to know how responsive it is when you click or interact with it.
FID specifically measures the time it takes for the website to respond after you've clicked a link or tapped a button. We want this delay to be short - ideally around 100 milliseconds or less for a good experience.
When the delay is longer, it means the website might be busy doing something else, like loading a big piece of code, which slows down its response to your clicks or taps. So, we aim to make this delay as short as possible to give users a smooth experience.

How to Measure FID

To measure FID, we use tools like
1. Chrome User Experience Report,
2. PageSpeed Insights,
3. Search Console( Core Web Vitals Report) or
4. web-vitals JavaScript library

These tools help us understand how well a website is performing in terms of responsiveness and where it might need improvements.
Improving FID involves optimizing how websites load and process information, making sure they respond quickly when users interact with them. This way, users get a better experience from the moment they land on the site.
Now, Let’s Have a Look over CLS

What is CLS?

CLS stands for Cumulative Layout Shift, and it's a metric used to measure visual stability on a web page.
Imagine you're reading an article, and suddenly, while scrolling, an image or a button loads, pushing down the content you were reading. That sudden shift or movement of elements on the page is what Cumulative Layout Shift measures.
In simpler terms, CLS gauges how much the elements on a web page move around while the page is loading. It quantifies the unexpected layout shifts users might experience, which can be annoying or disruptive when browsing a website.
A good CLS score means that when you're on a webpage, everything stays in place as it loads. It ensures a smooth and stable user experience without elements jumping around unexpectedly.

What is Good CLS Score?

A good CLS (Cumulative Layout Shift) score is typically considered to be less than 0.1. Scores below 0.1 indicate that the page has minimal unexpected layout shifts, providing a stable and user-friendly experience.
CLS scores are measured on a scale from 0 to 1, where lower values signify fewer unexpected shifts in the page layout during the loading process. Scores closer to 0 indicate better visual stability, ensuring that elements on the page remain steady and don't move around abruptly, creating a smoother user experience.
Here are some easy tips to reduce Cumulative Layout Shift (CLS):

  • Use specific size attributes for media: When adding things like images, videos, GIFs, or infographics, specify their dimensions. This helps the browser reserve the exact space needed for them, preventing sudden layout shifts as the page loads.
  • Reserve space for ads: Make sure there's a designated area for ads on your page. If they pop up suddenly without a reserved space, they can shift the content around, causing an unexpected layout change.
  • Place new design elements below the visible area: When adding new elements like buttons or images, position them below the visible part of the page initially. This way, they won’t unexpectedly move the content that users are already looking at.

Interaction to Next Paint (INP):INP measures how fast a webpage responds when you click or tap something after it's fully loaded. It's like checking how quickly the page reacts after it's all set.
Improving INP:To make this faster, you can do a few things. First, make sure JavaScript doesn't take too long to run. Also, try to limit third-party scripts, use a content delivery network (CDN), make images smaller without losing quality, and let browsers save some data for quicker loading.

How to check Core Web Vitals(LCP, FID & CMS) : Lab and Field
Field Tools (Real User Data)

  • Chrome User Experience Report: Real user data collected from Chrome browser users who have opted in, excluding iOS users.
  • Page Speed Insights:Provides performance insights based on real-user data.
  • Search Console (Core Web Vitals report): Shows Core Web Vitals data to site owners.
  • web-vitals JavaScript library: Allows measurement and tracking of web vitals like LCP.

Lab Tools (Simulated Environment)

  • Chrome Dev Tools: Offers simulated performance measurement within the browser.
  • Lighthouse: Integrated with Dev Tools, Lighthouse audits and provides performance reports.
  • Page Speed Insights: Besides field data, it also provides lab data for performance analysis.
  • Web Page Test: Simulates performance metrics from different locations and network conditions.


  • Field Tools: Utilize real user data for insights into actual user experiences.
  • Lab Tools: Simulate performance metrics in controlled environments for testing and optimization purposes.

Both field and lab measurements are crucial for understanding and improving Largest Contentful Paint and overall web performance.

People also ask
How is Core Web Vitals data free?

  • So, why is this Core Web Vitals data free, you ask? Well, summary report relies on the Chrome User Experience Report (CrUX) dataset, which gathers real user experiences from millions of websites. This data is collected mainly from Chrome browser users who chose to share their information, except for iOS users. That's how we're able to offer this data without charge.

  • How do I check my website's Core Web Vitals history?

  • Type in a website address to see its Core Web Vitals over time, using real data from how people actually use Chrome. Google Search Console let’s you see how well your website performs in terms of Core Web Vitals and pinpoint spots that might need some tweaking

  • Why should I measure my Core Web Vitals?

    • Measuring your Core Web Vitals is crucial because it helps ensure that your website offers a great experience to visitors. These vitals give you insights into how fast your site loads, how quickly it becomes interactive, and how stable it remains while users interact with it.
      Why does this matter? Well, users these days expect websites to load quickly and be easy to use. If your site takes ages to load or if it's clunky and unresponsive, people might leave before even exploring what you have to offer. Plus, search engines like Google consider Core Web Vitals when ranking websites, so good performance can actually boost your site's visibility in search results.
      By measuring these vitals, you can identify areas for improvement and make your website more enjoyable and efficient for visitors, which in turn can lead to higher engagement, happier users, and better search engine rankings.

    What is the Web Vitals extension?

    • The Web Vitals extension is a tool developed by Google to help developers and website owners assess the performance of their websites in real-time. It's essentially a browser extension, primarily designed for Google Chrome, that provides detailed insights into a website's Core Web Vitals metrics as users interact with it.
      This extension displays real-time data regarding the key performance metrics such as loading speed, interactivity, and visual stability. It offers a user-friendly interface that showcases these metrics, allowing developers to identify and diagnose any issues affecting the user experience.
      Web Vitals extension serves as a handy tool for developers and website owners to monitor their site's performance, identify potential problems, and optimize their websites for better user experiences based on Core Web Vitals metrics.
      Learn More:
      Content Delivery Network

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