What are Core Web Vitals

Search engines do not just evaluate what is on your page. They also measure how well your page performs for real visitors. Core Web Vitals are the specific website performance metrics used to assess page experience. They quantify loading speed, interactivity, and visual stability in ways that directly affect search rankings and visitor behavior.

Core Web Vitals are three measurable signals that reflect how quickly content appears, how responsively a page reacts to input, and how stable the layout remains while loading. Together they form the performance component of page experience, which search engines have used as a ranking factor since 2021. Understanding these metrics helps you prioritize the performance fixes that matter most.

What are the three Core Web Vitals?

Each metric targets a distinct aspect of the visitor experience. A page can score well on one and poorly on another, so all three need attention.

Largest Contentful Paint (LCP)

LCP measures how long it takes for the largest visible element on the page to fully render. That element is typically a hero image, a large heading, or a prominent text block. LCP reflects perceived load speed: the moment when the visitor feels the page has actually loaded rather than showing a blank or partially loaded screen.

• Good: 2.5 seconds or faster
• Needs improvement: 2.5 to 4 seconds
• Poor: above 4 seconds

Interaction to Next Paint (INP)

INP measures how quickly the page responds to user interactions throughout the entire visit. Clicks, taps, and keyboard input are all tracked. A low INP means buttons respond immediately, menus open without delay, and forms accept input without lag. INP replaced First Input Delay in 2024 because it captures responsiveness across the full session, not just the first interaction.

• Good: 200 milliseconds or below
• Needs improvement: 200 to 500 milliseconds
• Poor: above 500 milliseconds

Cumulative Layout Shift (CLS)

CLS measures unexpected layout movement while the page loads. Text that jumps when an image loads above it, buttons that shift position as ads appear, or fonts that swap and push content down all increase CLS. High CLS frustrates visitors who try to click an element that moves before their tap registers.

• Good: 0.1 or below
• Needs improvement: 0.1 to 0.25
• Poor: above 0.25

Why do Core Web Vitals matter?

Core Web Vitals affect both search visibility and visitor behavior. Search engines use them as part of page experience signals when ranking results. Pages that meet the "good" threshold for all three metrics have an advantage over similarly relevant pages that score poorly, particularly in competitive search results.

Performance metrics also correlate directly with business outcomes. Slow LCP increases bounce rates. High INP makes interactive elements feel broken. Poor CLS causes misclicks and abandoned forms. The article on why mobile page speed matters explains how these effects are amplified on mobile devices, where the majority of web traffic now originates.

How are Core Web Vitals measured?

Scores are based on real-world data collected from actual visitors, not just laboratory tests. Search engines aggregate performance data from users who visit your pages and calculate scores at the 75th percentile. This means at least 75 percent of visits must meet the "good" threshold for a page to pass.

What causes poor Core Web Vitals scores?

Each metric has distinct causes, which means fixes can be targeted rather than generic.

Poor CLS

Images and embeds without defined dimensions, dynamically injected content, and web fonts that cause text reflow are the main CLS culprits. Setting explicit width and height on images prevents most layout shifts.

For a broader look at performance troubleshooting, see the article on why a website is slow.

How WEMASY handles Core Web Vitals

WEMASY builds performance optimizations into the platform by default. Images are compressed and resized automatically. Caching is enabled without manual configuration. Pages are kept lean to reduce render-blocking resources. Core Web Vitals scores are visible in the WEMASY dashboard, showing LCP, INP, and CLS performance against the thresholds search engines use.

See what is included at the WEMASY website builder or review plans on the pricing page.

Frequently asked questions