What Are Core Web Vitals?
Van Isle SEO Knowledge Hub
Core Web Vitals provide a standardized way to measure parts of the real-world experience people have when loading and interacting with webpages.
They are part of a much larger performance picture. A website can technically pass its Core Web Vitals thresholds while still providing a poor user experience, and a website does not automatically rank higher simply because every metric is green.
Core Web Vitals are nevertheless valuable because they turn vague concepts such as “fast” or “responsive” into measurable performance signals that developers, marketers, and SEO teams can diagnose.
They form part of broader technical SEO and should be considered alongside crawlability, rendering, architecture, mobile usability, and conversion performance.
What Are the Three Core Web Vitals?
Content Asset 1
Core Web Vitals at a Glance
| Metric | Measures | User Experience Question |
|---|---|---|
| LCP | Loading performance | How quickly does the main visible content appear? |
| INP | Interaction responsiveness | How quickly does the page visually respond to user interactions? |
| CLS | Visual stability | Does content unexpectedly move while the page is being used? |
What Is Largest Contentful Paint?
Largest Contentful Paint measures how long it takes for the largest qualifying content element visible within the viewport to render.
Depending on the page, that element might be a hero image, large text block, banner, or another prominent element.
Slow LCP can be caused by slow server response, large unoptimized images, render-blocking CSS or JavaScript, delayed fonts, third-party scripts, or resources that are discovered too late in the loading process.
Improving LCP often requires identifying which specific element is being measured rather than applying generic speed recommendations blindly.
What Is Interaction to Next Paint?
Interaction to Next Paint measures the responsiveness of a webpage by evaluating the delay between user interactions and the next visual update.
Interactions can include clicking buttons, opening menus, selecting options, and other direct actions.
Poor INP can result from long JavaScript tasks, excessive third-party scripts, complex event handlers, large DOM structures, or heavy processing that blocks the main browser thread.
Improvement may require reducing JavaScript execution, breaking large tasks into smaller work, delaying nonessential code, and simplifying interactive components.
What Is Cumulative Layout Shift?
Cumulative Layout Shift measures unexpected movement of visible page elements.
A common example occurs when someone is about to click a button and an image, advertisement, banner, or late-loading component suddenly pushes the button to another position.
CLS problems often come from images without defined dimensions, dynamic advertisements, embedded content without reserved space, banners inserted above existing content, or font-loading behaviour.
Visual stability is a usability problem first
CLS is not merely an SEO score. Unexpected page movement can cause visitors to click the wrong element, lose their reading position, or abandon the page altogether.
What Is the Difference Between Field Data and Lab Data?
Field data measures experiences collected from real users over time. Those experiences vary according to devices, network quality, geography, browser conditions, and user behaviour.
Laboratory data comes from a controlled test environment. It is valuable for diagnosing problems because the conditions can be repeated, but it does not perfectly reproduce every real visitor.
A website can therefore have strong laboratory scores while real-user data remains poor, or the reverse.
Content Asset 2
Field Data vs. Lab Data
| Data Type | Best Used For | Limitation |
|---|---|---|
| Field data | Understanding actual visitor experience | Requires sufficient real-user data and reflects many uncontrolled conditions |
| Lab data | Debugging and controlled testing | Does not perfectly reproduce the full real-world audience |
Do Core Web Vitals Affect SEO Rankings?
Page experience and performance can contribute to search performance, but Core Web Vitals should not be treated as a shortcut to rankings.
A fast page with weak content, poor search intent alignment, or no authority does not automatically outrank a slower page that provides substantially more value.
The strongest reason to improve performance is therefore broader than SEO. Faster and more stable pages can improve usability, engagement, conversions, and customer satisfaction.
This is also where technical SEO connects with conversion rate optimization.
How Do You Measure Core Web Vitals?
Core Web Vitals can be reviewed through several Google tools and browser diagnostics.
Google Search Console groups URLs with similar Core Web Vitals issues. PageSpeed Insights provides performance information for individual URLs and combines available field information with laboratory diagnostics.
Browser developer tools and Lighthouse can help investigate specific loading and rendering causes.
Measurement should examine representative templates rather than testing only the homepage. Product pages, service pages, articles, location pages, and conversion pages may behave differently.
How Do You Improve Core Web Vitals?
Performance improvements should begin with diagnosis. Compressing every image or removing every script may create unnecessary work without fixing the actual measured problem.
Content Asset 3
Core Web Vitals Diagnostic Framework
| Problem | Review First |
|---|---|
| Poor LCP | Server response, hero assets, image size, loading priority, render-blocking resources |
| Poor INP | JavaScript tasks, third-party scripts, event handlers, DOM size, main-thread work |
| Poor CLS | Image dimensions, embeds, banners, dynamic content, fonts, reserved layout space |
Squarespace and other managed platforms control some infrastructure automatically, but third-party scripts, custom code, media, embedded tools, tracking, design choices, and page construction can still substantially influence performance.
Should Every Core Web Vitals Warning Be Fixed?
Not every performance opportunity deserves equal attention.
Prioritize problems affecting important landing pages, large percentages of users, conversion paths, mobile experiences, or templates used across hundreds of URLs.
A severe responsiveness issue on every service page is more important than a minor warning on an old article with almost no traffic.
The same impact-based approach applies throughout technical SEO auditing.
Frequently Asked Questions About Core Web Vitals
What are Core Web Vitals in simple terms?
Core Web Vitals are metrics measuring important parts of webpage loading, responsiveness, and visual stability.
What are the current Core Web Vitals?
The current Core Web Vitals are Largest Contentful Paint, Interaction to Next Paint, and Cumulative Layout Shift.
What happened to First Input Delay?
Interaction to Next Paint replaced First Input Delay as the responsiveness Core Web Vital. INP measures interaction responsiveness more comprehensively across the page experience.
Does a perfect PageSpeed score guarantee rankings?
No. Search rankings depend on many systems including relevance, intent, content quality, authority, and competition.
Is PageSpeed Insights the same as Core Web Vitals?
No. PageSpeed Insights is a tool that reports performance information and diagnostics, including Core Web Vitals where appropriate data is available.
Should I use field or lab data?
Use both. Field data describes real visitor experience, while lab testing helps reproduce and diagnose performance problems.
Can Squarespace websites pass Core Web Vitals?
Yes. Performance depends on the specific site, media, scripts, custom code, page structure, integrations, and visitor conditions rather than the CMS name alone.
Improve Performance Where It Actually Affects Users
Core Web Vitals are most valuable when they help identify genuine user-experience problems. The objective is not to chase a perfect score, but to make important webpages fast, responsive, stable, and easy to use.
Businesses can start with a free SEO competitor audit, explore Van Isle SEO services, or request a technical SEO consultation.