CSS & Rendering · AuditJet Glossary
Critical CSS
The minimal set of CSS required to render the above-the-fold content of a page without loading any external stylesheet.
Inlining critical CSS in the HTML <head> allows above-the-fold content to render without waiting for external stylesheets. The remaining non-critical CSS is loaded asynchronously. This technique improves FCP and LCP by eliminating the render-blocking behaviour of external CSS files. Tools like Penthouse, Critical, and Critters automate critical CSS extraction.
Related terms
CSS and JavaScript files that prevent the browser from rendering any page content until they have been downloaded and processed.
The time from page navigation start until any text, image, non-white canvas, or SVG is first rendered on the page.
The time from page navigation start until the largest image or text block visible in the viewport has finished rendering.
Frequently asked questions
What is Critical CSS?
The minimal set of CSS required to render the above-the-fold content of a page without loading any external stylesheet.
How does AuditJet measure Critical CSS?
AuditJet runs automated Google Lighthouse audits that surface Critical CSS scores alongside actionable fix guidance. You can track Critical CSS trends across all your pages and receive alerts when the metric regresses.
Monitor Critical continuously
AuditJet tracks Core Web Vitals on a schedule with revenue impact alerts — powered by Google Lighthouse and Google PageSpeed Insights.
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