Critical Css makes your site render blazingly fast — especially on mobile. Implementing critical css will improve your performance score on tools like WebPageTest and Google’s Pagespeed Insights, and improve your SEO.
CSS Stylesheets block rendering. Until a user’s browser has requested, received, downloaded and parsed your stylesheets, your page will remain blank. By reducing the amount of CSS the browser has to go through, we can get the page to render much, much faster.
Unfortunately it’s quite tedious to manually determine what css should be considered critical for a page. This tool removes that pain by automating this process.
criticalcss.com was created in 2015 by Jonas Ohlsson Aden in order to make the performance benefits of using critical css available to a wide audience. Prior to this Jonas had laid out the technical ground work to show how critical css could be automated, but during this process he realised that these solutions were quite technical and out of hands to most website owners. This was how the idea of criticalcss.com came to life - the idea that everyone should be able to have great performance on their website, regardless of technical expertise and website architecture. Today we’re proud to say that criticalcss.com is doing just that, automatically generating critical css for tens of thousands of web pages every day!