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Understanding Core Web Vitals

Core Web Vitals

A reel of film on a dark background helping users understand core web vitals.

Performance Metrics

What Is It?

Understanding Core Web Vitals

By: Simon | Category: Pagespeed
Published Date: 7th January, 2024

Google’s Core Web Vitals (CWV) initiative is at the forefront of web development, emphasising the importance of website performance in terms of user satisfaction.

As websites strive to meet these standards, understanding how to dissect and optimise Core Web Vitals scores becomes crucial. In this comprehensive guide, we will delve into the intricacies of CWV, exploring each metric and providing actionable insights for improvement.

What Are Core Web Vitals?

Core Web Vitals consist of three essential metrics: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). First Input Delay is soon to be replaced with Interaction To Next Paint (INP), which measures how fast your website reacts to user interactions.

These metrics focus on different aspects of user experience, including loading performance, interactivity, and visual stability. Google has set specific thresholds for each metric to categorise websites into different performance levels and gives you a score accordingly.

Largest Contentful Paint (LCP) – The Loading Experience

LCP measures the time it takes for the largest content element on a page to become visible. This element could be an image, video, or block-level text:

Identify The Largest Content Element: Use browser tools to see what contributes the most to LCP.

Optimise Critical Rendering Path: Minimise server response times and leverage browser caching.

Consider Lazy Loading: Prioritise loading of visible content first, deferring non-essential elements.

First Input Delay (FID) – Ensuring Interactivity

FID gauges the time a page takes to become interactive once initiated:

Identify Long Tasks: Use browser developer tools to pinpoint delays.

Optimise JavaScript Execution: Defer non-essential JavaScript, and leverage browser caching.

Prioritise Main Thread Activities: Ensure that critical tasks run on the main thread.

Cumulative Layout Shift (CLS) – Enhancing Visual Stability

CLS measures the unexpected layout shifts that occur during a page’s lifespan:

Identify Layout Shift Causes: Use tools to find elements causing shifts and adjust their properties.

Set Element Dimensions: Specify width and height attributes for images and iframes.

Implement Loading Placeholders: Reserve space for dynamically loading content.

Use Tools & Common Sense

Shhh – The Percentage Score

Is Not A Ranking Factor

Tools for Dissecting Core Web Vitals Scores

Google Pagespeed Insights

Google PageSpeed Insights is a valuable tool for assessing and dissecting Core Web Vitals scores. It provides a detailed breakdown of each metric, highlighting areas for improvement. The tool also suggests specific optimisations tailored to your website.

An open-source tool from Google, can be run as a browser extension or from the command line. It not only evaluates Core Web Vitals but also provides comprehensive insights into other performance aspects. Lighthouse generates a performance report with actionable recommendations for improvement.

Web Vitals Extension
The Web Vitals browser extension offers real-time feedback on a webpage’s Core Web Vitals performance. It provides a quick overview of LCP, FID, and CLS, allowing developers to identify issues promptly during development.

Checklist: Optimising Core Web Vitals Scores

Optimising Largest Contentful Paint (LCP)

Optimise Images: Compress and resize images without compromising quality.

Prioritise Critical CSS: Inline critical styles and defer non-critical styles for faster rendering.

Utilise A Content Delivery Network (CDN): Distribute assets across multiple servers globally to reduce latency.

Optimising First Input Delay (FID)

Minimise JavaScript Execution Time: Remove unused scripts and use asynchronous loading for non-essential scripts.

Optimise Third Party Scripts: Evaluate and limit the impact of third-party scripts on FID.

Implement Server Side Rendering (SSR): Generate HTML on the server to reduce client-side processing time.

Optimising Cumulative Layout Shift (CLS)

Set Dimensions For Images & Videos: Specify width and height attributes to prevent layout shifts.

Preload Content: Use the preload attribute to give browsers a hint about resources that will be needed later.

Monitor Third Party Content: Be cautious with third-party widgets or ads that may contribute to layout shifts..

My Conclusions

Mastering Core Web Vitals is not just a technical endeavor but a strategic move toward providing exceptional user experiences. By dissecting and optimizing LCP, FID, and CLS scores, web developers can ensure their websites meet the stringent standards set by Google.

Utilizing tools like Google PageSpeed Insights, Lighthouse, and the Web Vitals extension, combined with real-world case studies, provides actionable insights for achieving optimal Core Web Vitals performance. As we continue to prioritise user experience, the journey of dissecting and optimising Core Web Vitals scores remains a critical aspect of modern web development.

Technial blog author

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