Core Web Vitals: The Key to Supercharging Your Website‘s Performance and UX

You‘ve likely heard the buzz about Core Web Vitals over the past couple of years. But what exactly are these mythical metrics, and why have they become the obsession of SEO experts and web developers alike?

At their essence, Core Web Vitals are a set of specific factors that Google considers important in a webpage‘s overall user experience. Introduced in May 2020 and rolled out as part of the page experience update in 2021, they‘ve become a critical ranking factor and the new standard for assessing website performance.

"Core Web Vitals are a set of real-world, user-centered metrics that quantify key aspects of the user experience. They measure dimensions of web usability such as load time, interactivity, and the stability of content as it loads." – Philip Walton, Engineer at Google

But here‘s the kicker – a staggering 96% of sites are failing the Core Web Vitals assessment, according to 2022 data from Screaming Frog. This means that if you can optimize your site to pass, you‘ll be in the top 4% and have a significant advantage over your competitors.

Why Core Web Vitals Matter

So why all the fuss over these particular metrics? It all comes down to user experience. Google‘s mission is to "organize the world‘s information and make it universally accessible and useful." A big part of that is ensuring that the sites they rank high are not only relevant, but also provide a smooth, frictionless experience for users.

Enter Core Web Vitals. They focus on three aspects of user experience – loading, interactivity, and visual stability. Let‘s break each one down:

Largest Contentful Paint (LCP)

LCP measures loading performance. It looks at how long it takes for the main content of a page (such as a large image, video, or block of text) to load. Google considers an LCP of 2.5 seconds or less to be good.

Why it matters: A slow-loading page can lead to high bounce rates as impatient users click away. In fact, a 1-second delay in page load time can result in a 7% reduction in conversions.

First Input Delay (FID)

FID measures interactivity. It calculates the time from when a user first interacts with a page (like clicking a button) to the time when the browser is actually able to process that interaction.

Why it matters: If your site is unresponsive and users have to wait for their actions to take effect, it leads to a frustrating experience. 47% of consumers expect a web page to load in 2 seconds or less, and 64% of smartphone users expect pages to load in less than 4 seconds.

Cumulative Layout Shift (CLS)

CLS measures visual stability. It looks at how much the visible content of a page shifts unexpectedly as it loads (like if buttons or links move around as new content loads above them).

Why it matters: Unexpected layout shifts can be visually jarring and lead to accidental clicks, resulting in a poor user experience. 39% of people will stop engaging with a website if images take too long to load or the layout is unattractive.

Measuring Your Core Web Vitals

Now that we understand what the Core Web Vitals are and why they‘re important, let‘s dive into how you can measure them for your own site.

Google provides several tools to help with this:

  • PageSpeed Insights: Enter a URL and get a report on how that page performs on desktop and mobile, along with suggestions for improvement.
  • Lighthouse: An open-source, automated tool for improving the quality of web pages. It has audits for performance, accessibility, progressive web apps, SEO and more.
  • Search Console: Provides a Core Web Vitals report showing how your pages perform based on real-world usage data.
  • Chrome DevTools: Allows you to profile the runtime of a page, identify performance bottlenecks, and debug issues.
  • Chrome UX Report: A public dataset of real user experience metrics for millions of websites.

Here‘s a quick step-by-step guide for using PageSpeed Insights:

  1. Go to
  2. Enter the URL of the page you want to analyze
  3. Click "Analyze"
  4. Review the scores and suggestions in the report

In the report, you‘ll see scores for each of the Core Web Vitals metrics, as well as an overall performance score. These are categorized as Good, Needs Improvement, or Poor.

Here are the current benchmarks for each metric:

Metric Good Needs Improvement Poor
LCP ≤ 2.5s > 2.5s and ≤ 4s > 4s
FID ≤ 100ms > 100ms and ≤ 300ms > 300ms
CLS ≤ 0.1 > 0.1 and ≤ 0.25 > 0.25

Strategies for Optimizing Core Web Vitals

So you‘ve tested your site and found that your Core Web Vitals scores need some work. What now? Here are some strategies and tools for optimizing each metric:

Optimizing LCP

  • Minimize resource requests: Each resource (like an image, script, or stylesheet) requires a separate HTTP request. Reducing the number of requests can significantly speed up loading.

  • Leverage browser caching: Browser caching allows a user‘s browser to store a copy of your site‘s resources, so they don‘t need to be downloaded again on subsequent visits.

  • Optimize images: Images are often the largest resources on a page. Compress them, serve them in next-gen formats like WebP, and use responsive images to serve the right size for each device.

  • Implement lazy loading: Lazy loading defers the loading of non-critical resources until they‘re actually needed, speeding up the initial load.

Tools: ImageOptim, WebP Convert, lazysizes

Optimizing FID

  • Minimize main thread work: The browser‘s main thread handles user interactions, so any Javascript tasks that take a long time can block user input. Break up long tasks or move them to a separate thread.

  • Reduce Javascript execution time: Minimize and compress your Javascript files, and consider deferring or async loading scripts that aren‘t critical for the initial render.

  • Use a web worker: Web workers allow you to run scripts in background threads, freeing up the main thread for user interactions.

Tools: Terser, Closure Compiler, Comlink

Optimizing CLS

  • Include size attributes on images and videos: This allows the browser to allocate the correct amount of space in the document while the image is loading.

  • Reserve space for ads and embeds: If you have ads or embeds that load dynamically, reserve space for them in your layout to avoid shifts when they load.

  • Avoid inserting content above existing content: Unless it‘s in response to a user interaction, don‘t insert new content above existing content, as it will push everything else down and cause a layout shift.

Tools: Cumulative Layout Shift Debugger

Case Studies

Let‘s look at a couple of examples of companies that significantly improved their Core Web Vitals scores and the impact it had.

WP Engine

WP Engine, a WordPress hosting platform, saw impressive results after optimizing their Core Web Vitals:

  • LCP improved by 50%
  • CLS improved by 30%
  • Traffic from Google Search increased by 27%
  • Leads generated from Google Search increased by 20%

How they did it:

  • Upgraded PHP versions
  • Implemented server-level caching
  • Optimized images and fonts
  • Minified and compressed resources


DebugBear, a website monitoring service, also saw improvements after focusing on Core Web Vitals:

  • LCP improved from 3.1s to 1.3s
  • CLS improved from 0.9 to 0

How they did it:

  • Implemented critical CSS inline
  • Deferred non-critical Javascript
  • Optimized images
  • Preloaded key requests

These case studies demonstrate the real-world impact that optimizing Core Web Vitals can have, not just on user experience but on bottom-line metrics like traffic and leads.

The Future of Core Web Vitals

As mentioned earlier, Google will be replacing the FID metric with a new one called Interaction to Next Paint (INP) in 2024.

INP aims to capture a more complete picture of a page‘s responsiveness by measuring not just the first input delay, but the latency of all interactions a user has with the page. This shift indicates that Google is continuously refining its metrics to better represent real-world user experience.

Looking forward, it‘s likely that Core Web Vitals will continue to evolve. As web technologies and user expectations change, the metrics we use to assess user experience will need to adapt too.

For example, as more sites implement features like infinite scroll and single-page applications, metrics around smoothness of scrolling and navigation could be introduced. And as the web becomes increasingly visual and interactive, metrics around animation performance and input latency for complex gestures like drag-and-drop could become important.

The key for website owners and developers is to stay informed about these changes and be prepared to adapt your optimization strategies. Regularly testing your site, keeping your skills up-to-date, and staying engaged with the web performance community will be critical to staying ahead of the curve.

Wrapping Up

Core Web Vitals have become the new standard for assessing website performance and user experience. By understanding what they measure, how to assess them, and how to optimize for them, you can ensure your site is providing the best possible experience for your users.

But optimizing Core Web Vitals isn‘t a one-and-done task. It requires continuous monitoring, testing, and iteration. As Google‘s Philip Walton says, "The web is an everchanging platform. As it evolves, so do the expectations of those using it. Core Web Vitals help keep us accountable to meeting those expectations."

By making Core Web Vitals a priority and a regular part of your workflow, you‘re not just improving your search rankings. You‘re demonstrating a commitment to providing an excellent user experience, and that‘s something that will pay dividends far beyond any algorithm update.