Render-Blocking Resources
Resources like CSS and JavaScript that prevent the browser from rendering content until they're downloaded and processed.
Quick Definition
Resources like CSS and JavaScript that prevent the browser from rendering content until they're downloaded and processed.
Full Explanation
Render-blocking resources are files that prevent the browser from rendering any content until they're fully downloaded and processed. By default, CSS is render-blocking because the browser needs to build the CSSOM before painting. JavaScript in the head is also render-blocking by default. Render-blocking resources directly impact FCP and LCP. To reduce their impact: inline critical CSS, defer non-critical CSS, add async or defer attributes to scripts, and remove unused CSS/JS. The goal is to get something on screen as quickly as possible while loading non-critical resources in the background.