Render Blocking

Technical Definition

Render blocking occurs when CSS or JavaScript files prevent the browser from displaying content until they're loaded and processed. By default, CSS blocks rendering and JavaScript blocks parsing. Mitigation strategies: inline critical CSS, defer non-critical JS, async load non-critical resources, eliminate unused CSS/JS. Critical for improving LCP and perceived performance.

Simple Explanation (ELI13)

Render blocking is when your website can't show anything until certain files finish loading. It's like waiting for one slow person before everyone can enter. Some CSS and JavaScript files block everything. The fix is to load only what's needed first and delay the rest until after the page displays.

Related Terms

Critical CSS, JavaScript Optimization, LCP, Page Speed

Learn More

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