Core Web Vitals: LCP, INP & CLS Explained

Core Web Vitals are standardized performance metrics designed to measure aspects of a page that users actually experience.

The three current metrics are:

Metric

Measures

Good Target

LCP

Loading performance

≤ 2.5 seconds

INP

Responsiveness to interactions

≤ 200 ms

CLS

Visual stability

≤ 0.1

Google recommends evaluating these metrics at the 75th percentile, separately for mobile and desktop experiences.

Largest Contentful Paint (LCP)

LCP measures loading performance. It represents how quickly the largest visible content element, such as a large image, video poster, or significant text block, becomes rendered.

A good LCP is 2.5 seconds or less. A slow LCP can be caused by factors such as slow server response, render-blocking resources, large images, or delays in loading important resources.

Interaction to Next Paint (INP)

INP measures how responsive a page is when users interact with it. It considers interactions such as clicks, taps, and keyboard input throughout the page visit.

An INP of 200 milliseconds or less is considered good. Between 200 and 500 milliseconds needs improvement, while values above 500 milliseconds are considered poor.

Common causes of poor INP include excessive JavaScript execution, long tasks, inefficient event handlers, and a busy main thread.

Cumulative Layout Shift (CLS)

CLS measures visual stability. It identifies unexpected movement of visible page elements while the page is loading or being used.

A CLS score of 0.1 or less is considered good. Unexpected movement can occur when images do not have reserved dimensions, advertisements load dynamically, fonts cause layout changes, or content is inserted above existing content.

Improving Core Web Vitals usually requires collaboration between SEO professionals, developers, designers, and content teams.

Improve LCP

Focus on the resources that determine how quickly the primary content becomes visible.

Practical improvements include:

• Optimize and properly size important images.
• Use modern image formats where appropriate.
• Reduce server response time.
• Minimize render-blocking CSS and JavaScript.
• Prioritize critical resources.
• Avoid unnecessarily large third-party scripts.
• Use effective caching and content delivery infrastructure.

Improve INP

Improving INP is largely about reducing the amount of work the browser needs to perform during user interactions.

Consider:

• Breaking up long JavaScript tasks.
• Reducing unnecessary JavaScript.
• Optimizing event handlers.
• Deferring nonessential scripts.
• Removing unused code.
• Reducing expensive DOM operations.
• Reviewing third-party scripts that consume main-thread resources.

Improve CLS

Visual stability requires reserving space for content before it loads.

Useful practices include:

• Specify width and height for images.
• Reserve space for advertisements and embedded content.
• Avoid inserting content above existing content unexpectedly.
• Manage web fonts carefully.
• Review dynamic components that change dimensions after rendering.

Core Web Vitals and page speed are related, but they are not exactly the same thing.

A website can have a high overall performance score in a laboratory test while still experiencing problems for some real users. Similarly, reducing the total page size alone does not necessarily solve an interaction or layout stability problem.

The more useful approach is to identify which user experience is failing and why:

• Slow primary content → investigate LCP
• Delayed clicks or taps → investigate INP
• Unexpected movement → investigate CLS

This makes optimization more targeted and practical.

Core Web Vitals provide a practical framework for understanding how users experience a website's loading performance, responsiveness, and visual stability. LCP, INP, and CLS help SEO teams and developers identify specific performance problems and prioritize meaningful improvements.

Rather than chasing a perfect score, focus on delivering pages that load important content quickly, respond reliably to interactions, and remain visually stable. This user-first approach aligns Core Web Vitals with broader technical SEO and overall website quality.