Core Web Vitals And On-Page Optimisation | Lillian Purge

Core Web Vitals and on-page optimisation

Core Web Vitals and on-page optimisation are often discussed as if they are separate disciplines, one technical and one content driven. In my experience that separation causes a lot of confusion and poor prioritisation. Core Web Vitals are not just technical metrics for developers, they directly influence how users experience a page, and that experience feeds straight back into on-page SEO performance.

On-page optimisation is ultimately about helping users get what they need easily and confidently. Core Web Vitals measure whether your page actually allows that to happen without frustration. When these two are aligned pages tend to perform more consistently. When they are treated in isolation SEO becomes unstable, even if rankings look fine on the surface.

In this article I want to explain how Core Web Vitals fit into on-page optimisation properly, what they really measure, and how to improve them without damaging content quality or user intent.

What Core Web Vitals actually measure

Core Web Vitals are a set of user experience metrics that Google uses to assess how pages behave for real users. They focus on three specific areas, loading speed, interactivity, and visual stability.

Largest Contentful Paint measures how quickly the main content of a page becomes visible. Interaction to Next Paint measures how responsive the page feels when a user tries to interact. Cumulative Layout Shift measures whether the page jumps around unexpectedly as it loads.

From experience these metrics matter because they capture frustration. A page can look good and still feel broken if it loads slowly, ignores clicks, or shifts content unexpectedly.

Why Core Web Vitals are part of on-page SEO

On-page SEO is not just about what is on the page, it is about how the page behaves. If users cannot read, scroll, or interact comfortably then the content may as well not exist.

From experience pages with poor Core Web Vitals often show weaker engagement signals. Users leave earlier, scroll less, and are more likely to return to search results. Google observes this behaviour and adjusts rankings over time.

Core Web Vitals therefore act as a bridge between technical performance and user behaviour, which makes them directly relevant to on-page optimisation.

Largest Contentful Paint and content visibility

Largest Contentful Paint is closely tied to content delivery. It measures how quickly the main piece of content appears, usually a heading, image, or large text block.

From experience pages that delay showing their core message feel slow even if the rest of the page loads eventually. Users start judging the page before everything finishes loading.

On-page optimisation should ensure that the most important content appears first. This often means prioritising critical text and images, reducing render blocking scripts, and avoiding heavy media above the fold.

Good content that loads late performs worse than average content that loads promptly.

Interaction to Next Paint and usability

Interaction to Next Paint reflects how responsive a page feels when someone tries to interact with it. This includes clicking buttons, opening menus, or typing into forms.

From experience pages that are visually loaded but unresponsive feel broken. Users click, nothing happens, and trust drops instantly.

On-page optimisation needs to consider how scripts, animations, and plugins affect responsiveness. Heavy JavaScript that blocks interaction undermines even the best written content.

A page that responds immediately feels professional and trustworthy.

Cumulative Layout Shift and reading flow

Cumulative Layout Shift measures how much the layout moves unexpectedly while a page loads. This often happens when images, fonts, or ads load without reserved space.

From experience layout shifts are extremely frustrating, especially on mobile. Users try to read or tap something and the page moves underneath them.

On-page optimisation includes maintaining a stable reading experience. Reserving space for images, avoiding late loading banners, and managing font loading all contribute to this.

Stable pages keep users engaged longer, which supports on-page SEO signals.

How Core Web Vitals influence engagement metrics

Core Web Vitals do not directly measure engagement, but they strongly influence it.

From experience pages that meet Core Web Vitals thresholds tend to show lower bounce rates, deeper scroll behaviour, and higher conversion completion. Users simply find it easier to use the page.

Google does not need to guess whether the page works. User behaviour tells the story clearly.

Improving Core Web Vitals often improves on-page SEO indirectly through better engagement rather than direct ranking boosts.

Why perfect scores are not the goal

One of the biggest mistakes I see is chasing perfect Core Web Vitals scores at the expense of content quality.

From experience removing helpful content, stripping images, or disabling useful features just to improve metrics often harms conversions and user trust.

On-page optimisation is about balance. Pages need to be fast enough and stable enough to avoid frustration, not sterile or empty.

Good SEO comes from pages that feel usable, not pages that win performance benchmarks.

Mobile Core Web Vitals matter more than desktop

Google evaluates Core Web Vitals primarily through mobile data. This is critical for on-page optimisation.

From experience many pages pass Core Web Vitals on desktop but fail on mobile due to slower devices, weaker networks, and heavier scripts.

On-page optimisation must prioritise mobile experience. Content layout, image sizes, and interaction patterns should be designed for small screens first.

If a page works well on mobile it usually works well everywhere.

Images and media as a Core Web Vitals factor

Images are one of the biggest contributors to Core Web Vitals issues.

From experience uncompressed images, large hero banners, and poorly implemented galleries slow down content visibility and cause layout shifts.

On-page optimisation should include image sizing, compression, and lazy loading where appropriate. Images should enhance understanding, not delay it.

Visual content must be treated as part of performance, not decoration.

Fonts, scripts, and third party tools

Custom fonts and third party tools often create hidden Core Web Vitals problems.

From experience late loading fonts cause layout shifts and tracking scripts block interactivity. These issues are often overlooked because they are not part of the visible content.

On-page optimisation should audit every script and font to ensure it justifies its cost in performance.

If a feature does not improve user experience it should not slow the page down.

Core Web Vitals and content hierarchy

Content hierarchy plays a role in Core Web Vitals performance.

From experience pages that clearly define what matters most load and render more predictably. Pages with cluttered headers, multiple competing elements, or complex above-the-fold layouts struggle.

On-page optimisation should simplify the initial view. Show the main message clearly, then layer additional content progressively.

Clarity improves both performance and comprehension.

How Core Web Vitals affect competitive SERPs

Core Web Vitals are rarely the deciding factor in isolation, but they matter in competitive environments.

From experience when several pages offer similar content quality, the page that feels faster and more stable often performs better over time.

This is especially true in local SEO and service based searches where users compare options quickly.

Core Web Vitals act as a tie breaker rather than a primary driver.

Measuring Core Web Vitals correctly

Lab tools are useful, but real user data matters more.

From experience Google’s field data reflects how actual users experience the page, not ideal conditions. This is what ultimately influences evaluation.

On-page optimisation should be guided by real world performance, not just simulated scores.

Improvements should be tested, measured, and validated against behaviour.

Integrating Core Web Vitals into on-page workflows

Core Web Vitals should be considered during content creation, not bolted on afterwards.

From experience designing pages with performance in mind produces better outcomes than retrofitting fixes later.

Writers, designers, and developers should align around delivering clear content efficiently rather than maximising features.

On-page SEO works best when performance is part of the design process.

Common mistakes when addressing Core Web Vitals

The most common mistakes are over prioritising metrics, ignoring mobile data, and treating performance as purely technical.

From experience Core Web Vitals problems often stem from content and layout decisions, not just code.

Fixing them requires collaboration, not just optimisation.

How I approach Core Web Vitals in practice

I start by identifying whether users are actually experiencing frustration.

If engagement is strong and conversion is healthy, minor metric failures may not be the priority. If users leave quickly or complain about usability, Core Web Vitals often explain why.

I then focus on the biggest sources of friction rather than chasing marginal gains.

This approach keeps on-page optimisation grounded in reality.

Final thoughts from experience

Core Web Vitals and on-page optimisation are tightly connected because both exist to serve users.

I think many sites struggle because they optimise content and performance separately, creating pages that are either fast but empty or rich but frustrating.

From experience the best performing pages are those that load quickly enough, behave predictably, and deliver clear useful content without friction.

When Core Web Vitals support on-page optimisation rather than compete with it, SEO performance becomes more stable, more resilient, and more predictable over time.