What are Core Web Vitals?
Core Web Vitals are a set of performance metrics defined by Google to measure real-world user experience on a website.
They focus on three key aspects: loading performance (Largest Contentful Paint), interactivity (Interaction to Next Paint), and visual stability (Cumulative Layout Shift).
Together, these metrics help Google evaluate how fast, responsive, and stable a page feels to users.
Core Web Vitals are also part of Google’s page experience signals and can influence search visibility.
Further Reading: How to optimize for website speed | Site speed checklist
Why Core Web Vitals Matter in SEO
Core Web Vitals matter in Search Engine Optimization because they measure real user experience, including loading speed, responsiveness, and visual stability—factors Google uses to evaluate page quality.
Site speed is a confirmed SEO ranking factor, and strong Core Web Vitals scores help improve rankings, engagement, and overall search performance.
What is Google PageSpeed Insights?
Google PageSpeed Insights is a free tool that analyzes a webpage’s performance across mobile and desktop devices. It reports Core Web Vitals using both real-user data (field data) and lab-based performance tests.
The tool also provides actionable recommendations, such as reducing render-blocking resources or improving image delivery.
PageSpeed Insights is commonly used by developers and SEO teams to diagnose and improve website speed and user experience.
What PageSpeed Insights Score tell you?
Google PageSpeed Insights evaluates your page across the following categories:
Performance: A weighted score based on metrics such as First Contentful Paint (FCP), Speed Index, Total Blocking Time (TBT), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS), reflecting overall speed and loading efficiency.
Accessibility: Assesses how usable your site is for all users, including navigation, image alt text, and color contrast for visual accessibility.
Best Practices: Measures adherence to modern web development standards, including secure connections, optimized and up-to-date code, and effective JavaScript usage.
SEO (Search Engine Optimization): Evaluates how well your page is optimized for search engines, covering metadata, structured data, and mobile-friendliness.
Core Web Vitals Metrics Explained:
In this section, we’ll explain the meaning of each Core Web Vitals metric in simple terms, provide easy-to-understand examples, and show how to optimize them.
1) Largest Contentful Paint (LCP) - visual load speed
Largest Contentful Paint (LCP) measures the time taken for the largest element on the page (usually an image or video) to become visible to users on a page.
How to optimize LCP:
Images: Resize image dimensions, reduce file size with compression, and use modern formats like WebP.
Videos: Compress video files using tools like HandBrake to reduce load time without sacrificing quality.
2) Interaction to Next Paint (INP) - interactivity, responsiveness
Interaction to Next Paint (INP) measures how quickly a webpage responds visually after a user interaction, such as clicking a button or tapping a link.
3) Cumulative Layout Shift (CLS) - visual stability
Cumulative Layout Shift (CLS) measures how much visible elements on a page unexpectedly move after the page starts loading, which can lead to a poor user experience.
Common causes of CLS:
Common causes of CLS include dynamically injected content such as ads, embeds, and iframes, as well as images or videos missing defined height and width attributes.
Fonts can also impact CLS because web fonts must be downloaded before they are displayed, which may cause text to shift.
To reduce CLS, it’s safest to use system fonts like Arial, Times New Roman, Helvetica, or Verdana, or limit web font usage by choosing a single font for headings or special sections only.
4) First Contentful Paint (FCP)
First Contentful Paint (FCP) measures how long it takes for the first visible content—such as text, an image, or an icon—to appear on the screen when a page starts loading.
Poor FCP is commonly caused by heavy themes, excessive or poorly optimized plugins, and page elements that block rendering, such as large scripts or unoptimized stylesheets.
5) First Input Delay (FID)
First Input Delay (FID) measures the time it takes for a webpage to respond to a user’s first interaction, such as clicking a button or tapping a link, after the page begins loading.
6) Time to First Byte (TTFB)
Time to First Byte (TTFB) measures how long it takes for the browser to receive the first byte of data from the server after a request is made, reflecting server response speed and backend performance.
7) Total Blocking Time (TBT)
Total Blocking Time (TBT) measures the amount of time a page is blocked from responding to user interactions due to long-running JavaScript tasks during loading.
To reduce blocking time, minify JavaScript files and defer or delay JavaScript execution so the browser can become interactive faster.
8) Speed Index
Speed Index measures how quickly the visible, above-the-fold content of a webpage is displayed during page load.
Other Site Speed Checking tools:
Google PageSpeed Insights is usually sufficient for most performance analysis. However, there are other popular alternatives you can use for additional insights, such as GTmetrix and Pingdom.
Should I just optimize for homepage or all pages on ur website?
Focus on optimizing the most important pages on your site, such as the homepage, product or service pages, and pages that drive the most traffic or rank for many keywords, rather than trying to optimize every page at once.
What are HTTP requests?
HTTP requests are calls made by the browser to load page resources such as HTML, CSS, JavaScript, images, and fonts from a server.
HTTP/1 vs HTTP/2: What’s the difference?
HTTP/1 loads files one at a time, while HTTP/2 can load multiple resources simultaneously, making pages faster and more efficient.
Raw HTML vs Rendered HTML: What’s the difference?
Raw HTML is the original code sent by the server, while rendered HTML is the final page after JavaScript runs and the browser builds what users actually see.
What is JavaScript & CSS?
JavaScript is a programming language that adds interactivity and dynamic behavior to websites, such as animations, forms, and user actions.
CSS (Cascading Style Sheets) controls how a website looks, including layout, colors, fonts, and responsiveness across devices.
What is render-blocking JavaScript?
Render-blocking JavaScript delays page rendering because the browser must download and execute the script before displaying visible content.
What is an iframe?
An iframe (inline frame) is an HTML element used to embed content from another webpage—such as videos, maps, or ads—inside a page, which can impact page speed if overused or not optimized.
What is a kibibyte (KiB)?
A kibibyte (KiB) is a unit of digital data equal to 1,024 bytes, commonly used to measure file sizes in web performance tools.
What is a Server?
A server is a system that stores website files and delivers them to users’ browsers when a page is requested. Web servers like Apache, Nginx, and LiteSpeed handle requests, manage traffic, and play a major role in website speed and performance.
What is Server-Side Rendering (SSR)?
Server-side rendering (SSR) is a technique where a webpage is fully generated on the server and sent to the browser as ready-to-display HTML, resulting in faster initial load times and improved SEO compared to client-side rendering.
What is the DOM (Document Object Model)?
The DOM is a structured representation of a webpage that the browser uses to display content and handle interactions. A large or complex DOM can slow down rendering and negatively impact performance.
Tools like Google Chrome DevTools help analyze DOM size and identify optimization opportunities, though implementing changes often requires developer support.