Core Web Vitals and Their Relationship to SEO

Web Vitals as Indicators of Marketability

Core Web Vitals are a set of user-focused performance metrics that Google has introduced to help measure and predict the real-world experience of users on your site. They are not based on real conditions in the strict sense, but rather, your site is measured within a predetermined testing environment. These metrics focus on factors like: how quickly your site loads, how responsive it is, how stable it is during page load, etc. By optimizing these metrics, you’re improving both the user experience and SEO.

The dominant part of SEO today is User Experience (UX), and Core Web Vitals offer a straightforward, measurable way to gain insight into this. Therefore, Google wants and expects sites that load fast, interact smoothly, and offer a visually stable experience — it is the bare minimum in 2025. Sites that perform poorly in these areas risk losing visibility in search engine results.

The Core Web Vitals Metrics

Core Web Vitals consist of three key metrics that Google uses to measure user experience on your website:

• Largest Contentful Paint (LCP) — Measures loading performance. LCP marks the point in the page load timeline when the largest content element is rendered. To provide a good user experience, LCP should occur within 2.5 seconds of the page starting to load.
• Interaction to Next Paint (INP) — Measures overall responsiveness. INP evaluates the time it takes for the page to respond to user interactions (clicks, taps, key presses) across its lifecycle. A good user experience is indicated when INP is less than 200 milliseconds.
• Cumulative Layout Shift (CLS) — Measures visual stability. CLS looks at how much visible content shifts on the screen during the page load. To provide a good experience, CLS should be less than 0.1.

In my own work, I have found that if your build pipeline is set up correctly, the only real post-build optimization needed is for LCP issues. Everything else is handled by well-formatted and thought-out optimization automations and smart asset usage.

I outline my preferred stack in my article My Exact Web Design Stack.

Let’s break them down further.

Largest Contentful Paint (LCP)

LCP measures how quickly the main content of your page loads, which helps you gauge how fast users can start consuming your content and how well you can maintain their attention. A standard rule of thumb is that if your LCP score is above 2.5 seconds, Google has communicated that that is a signal your page is taking too long to load, and this can cause not only a high bounce rate from poor user experience, but also factor into your site’s Google ranking profile. Luckily, improving LCP is the most straightforward and common issue to resolve on individual pages — optimize your images, reduce render-blocking resources, leverage browser caching, and consider newer media formats. If you want to learn more about the connection between speed and SEO boosts, my article Why Performance Impacts SEO.

<img
  src="/assets/images/blog/performance/sample-hero.webp"
  alt="Example LCP optimization"
  width="1200" height="630"
  loading="eager" decoding="async" fetchpriority="high"
  class="rounded-lg shadow"
/>

Interaction to Next Paint (INP)

INP is critical to ensuring your page responds to user interaction quickly and consistently. Every internet user has experienced the seemingly endless loading icon of doom at one point or another — debating whether or not the wait is worth their time and effort. If there is a long delay between user actions and the page’s response, the most overwhelming reaction will likely be frustration. Frustrated customers do not make for good business, and like it or not, our culture does not have dial-up patience anymore. Minimizing JavaScript execution, trimming long tasks, and reducing scripts blocking the main thread are key strategies to improving INP — mainlining externalized JS during a Static Site build is standard best practice currently, but there are many ways to achieve the same result. Remember: In programming, having a single "source of truth" file is ideal when possible, but business and life rarely afford that level of clarity in causation.

<script src="/assets/js/app.js" defer></script>

<!-- Avoid inline blocking JS, always defer or async where possible -->
<script src="/assets/js/vendor/chart.js" async></script>

Cumulative Layout Shift (CLS)

CLS measures the visual stability of your site. A high CLS means your content shifts unexpectedly, such as when images or text move around as the page loads. To improve this, always specify size attributes for images and videos and avoid dynamically injected content that may cause layout shifts.

<img
  src="/assets/images/blog/example-cls.webp"
  alt="Stable image with defined dimensions"
  width="800" height="600"
  loading="lazy" decoding="async"
/>

<!-- Container for ads or embeds with reserved space -->
<div style="min-height:280px;" class="ad-slot"></div>

Core Web Vitals Affect Search Engine Optimization (SEO)

Yes, Google has made it clear that Core Web Vitals are an important ranking factor, and if that's not reason enough, think of the other consequences: poor UX, brand degradation, lack of pride in your assets, minimization of your sales/marketing pipeline — the list goes on. Sites that score poorly on these metrics are also guaranteed to be demoted in search rankings, even if their content is top-notch... do you really want to sink countless hours producing quality content and cultivating user journeys only to be effectively invisible due to technical oversight? The currency of our time is attention, and search engines are acknowledging this by actively increasing how much they prioritize user experience as a critical factor for individual site success, especially in competitive search blocks.

Website curation is progressive and systemic when done well, and chronicled in the sense that each layer builds upon prerequisites from the last. So, design away without consideration for the ground beneath you, but remember that you are building on shifting sands — and that is a choice.

"But Mason, is it a choice? Business owners have enough on their plate — administrative loads, accounting, customer relations, training — you name it!"

I am sympathetic. I truly am. I remember what it was like to not have a technical grasp on front-end development. Painful. Trying. Frustrating. Here is the good news: you don't need to know it all tomorrow, the knowledge will pay off exponentially, and if you choose to educate yourself and invest in the right resources you might just build a presence that lasts.

It isn't just UX concerns or direct rankings that are at stake. It is also basic indexation. Think about it: If it takes 10s a page for a GoogleBot to crawl your site, how many pages will they crawl compared to if each page took 2.5s to load? While large, well-established sites have almost real-time indexation occurring... chances are you are not one of them yet. That means you have a limited crawl budget from the search engine providers that matter. Do you really want to waste your opportunity to gain traction because drag-and-drop sites are "easier" or "cheaper?"

<!-- Example: preconnect and preload to reduce crawl/render time -->
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link rel="preload" href="/assets/css/output.css" as="style">
<link rel="stylesheet" href="/assets/css/output.css">

Core Web Vitals Close or Open Doors For You

The landscape of SEO is intensely competitive, more so than many business owners realize. You compete with hordes of other voices: bots, competitors at every level from local to global, and AI mills. Core Web Vitals provide an additional layer of differentiation that other sites do not have — while sources differ, it is generally accepted that only 2-10% of all sites have Lighthouse scores of 95+ on every page. Just having the technical aspect alone puts you ahead of the vast majority of noise. If competitive sites have beautiful design work, great UX/UI implemented, well-packaged products, brand narratives, etc. — one of the only competitive advantages available is to outperform them at the roots. Appeal to the algorithms by making your code Google Catnip.

Wondering if the switch is tight for you? Check out my ROI calculator, based on industry averages, to find out.

With a solid focus on these metrics, you can ensure your website is prepared not only for today’s SEO demands but also for future changes to search algorithms. The point is to stay ahead of the game instead of playing catch-up all the time.

The Bottom Line: Optimizing Core Web Vitals is a Must

Core Web Vitals are a critical piece of the SEO puzzle. Optimizing these metrics is no longer optional, but essential for ranking well and providing a top-notch user experience. Google’s algorithms are smarter than ever, especially with the rising tide of AI.

So, if you want to stay ahead of the competition and ensure your site gets the attention it deserves, start optimizing your Core Web Vitals today. The results will be worth it in the long run.