Why and how to minify your JS and CSS

If you check your site speed with Google PageSpeed Insights you might get the advice to minify your Javascript (JS) and Cascading Style Sheets (CSS) files. Your JS files contain the code for the interactive elements of your website. And in your CSS files, you specify the design of your pages. Minifying those files will decrease your page load time, thereby providing a better user experience.

We received the following question about minification of JS and CSS files in our Ask Yoast inbox:

“Why and how should I minify my JS and CSS files?”

Check out the video or read the answer below!

Minify your JS and CSS files

“JavaScript (JS) is the stuff that makes your web page interactive and CSS is the stuff that makes your web page look good. Basically, these two things are code that you send to the browser, and that the browser needs to render.

A browser, like any other computer program, doesn’t care what the language that it receives, looks like. It doesn’t need the spacing and the comments and all other stuff, that your developer needs to make sense of it all. He needs the structure to get through the code, however, the browser has no benefit from that.

Stripping all of that down actually makes the file that you send to the user a lot smaller. Because when you minify it, you remove all the extra spaces, all the line breaks, and all the comments. Stripping all that can save up to 30-40%, or even 50% of file size in some cases. There really is no benefit of sending that stuff to the end-users, so minifying saves time and money for everyone. 

That’s why you should do it. Good luck!”

If you’re on WordPress, there’s a vast amount of plugins that can help you minify your HTML, CSS and JS files. We generally recommend WPRocket for this and some further improvements to speed up your site.

Read more: How to optimize browser caching »

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