What Are the Most Effective Ways to Minimize Unused CSS and JavaScript for Faster Rendering and Better Core Web Vitals Scores?


Minimizing unused CSS and JavaScript can significantly speed up your web page rendering, and improve your Core Web Vitals scores. To achieve this, various methods can be applied, such as using code coverage tools, removing unused code manually or with tools like PurifyCSS, and tree shaking. Working on minimizing main-thread work and using only essential JavaScript also contribute greatly to these performance benefits.

Using Code Coverage Tools

Chrome DevTools Coverage

Chrome DevTools provides a coverage tab which allows you to see how much CSS and JavaScript code is not used on your page. This helps identify and eliminate unused code, reducing file sizes and improving load time [Chrome DevTools Coverage, 2021].

Removing Unused Code

Manual Removal

Eliminate unused code manually by reviewing your code base for unused styles and scripts. Keep in mind that this is an error-prone process and requires detailed knowledge of the project.

Tools like PurifyCSS

Use tools such as PurifyCSS that detect and remove unused CSS code. These tools analyze your codebase and take out styles that are not being used, reducing the size of your CSS file [PurifyCSS, 2022].

JavaScript Tree Shaking

Webpack Tree Shaking

Webpack is a powerful tool that supports tree shaking, a process that removes unused code from your JavaScript bundle. This ensures your delivered code contains only what is absolutely necessary to run your application [Webpack Guides: Tree Shaking, 2023].

Minimizing Main-Thread Work

Reduce JavaScript Execution Time

Try to minimize how long the main thread is blocked by scripts. Optimize your JavaScript to minimize its impact on the main thread by deferring, splitting, or delaying execution of non-essential scripts [Mainthread Work Breakdown, 2023].

Using Only Essential JavaScript

Load JavaScript Dynamically

Dynamic imports in JavaScript allow you to load code on demand by using promises or the async/await syntax. This results in smaller bundle sizes and faster load times [Reduce JavaScript Payloads with Code Splitting, 2023].


Taking active steps to minimize unused CSS and JavaScript not only helps in delivering a faster, more efficient user experience, but also benefits SEO by improving Core Web Vitals scores. Utilizing tools and techniques such as code coverage, strategic removal of unused code, tree shaking, and reduction of main-thread work contribute significantly to these improvements.