URL: /glossary/render-blocking-resources
---
title: "Render-blocking resources: what blocks first paint"
description: "Render-blocking resources are the stylesheets and scripts in head a browser must load before its first paint. Which ones count, and how to unblock them."
sidebarTitle: "Render-blocking resources"
---
**Render-blocking resources** are the files a browser has to download and process before it can paint anything: stylesheets in `` and classic scripts in `` without `async` or `defer`.
Lighthouse's criteria are specific. A `` blocks unless it is `disabled` or its `media` does not match the device. A `
```
The `media="print"` stylesheet downloads without blocking and switches on once loaded ([the render-blocking fix](/rules/perf/render-blocking#how-to-fix-it)). Replace each `@import` with its own ``, so the browser fetches the files in parallel ([the request chain fix](/rules/perf/critical-request-chains#how-to-fix-it)). Preconnect to two to four origins on the critical path at most, with `crossorigin` for fonts ([the preconnect fix](/rules/perf/preconnect#how-to-fix-it)).
## Run the check
{/* glossary:run:start */}
```bash
squirrel audit https://example.com --rule-include perf/render-blocking,perf/critical-request-chains,perf/preconnect
```
{/* glossary:run:end */}
A signed-out local audit costs nothing.
{/* glossary:related:start */}
## Related terms
- [Largest Contentful Paint (LCP)](/glossary/lcp): The time until the largest image or text block in the viewport renders; good is 2.5 seconds or less.
- [font-display](/glossary#font-display): The @font-face descriptor (swap, optional, fallback) that decides what text shows while a web font loads.
{/* glossary:related:end */}
## References
- [Eliminate render-blocking resources, Chrome for Developers](https://developer.chrome.com/docs/lighthouse/performance/render-blocking-resources)
- [Establish network connections early, web.dev](https://web.dev/articles/preconnect-and-dns-prefetch)
- [The script element, MDN](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/script)