--- title: "Render-blocking resources delay first paint (perf/render-blocking)" description: "perf/render-blocking: Synchronous scripts in and large stylesheets stop the browser from painting until they are fetched and executed." canonical: https://void-design.vercel.app/rules/perf/render-blocking lastModified: 2026-09-16 --- # Render-blocking resources delay first paint `perf/render-blocking` · severity **warn** · category Performance · detected by `void perf` and `void audit` ## Why it matters Synchronous scripts in and large stylesheets stop the browser from painting until they are fetched and executed. ## How to fix it Add defer or type="module" to scripts, load third-party tags async/lazily, and keep blocking CSS small. ## Example ``` ``` ## More performance rules `void perf` reports 25 rules in this category. Core Web Vitals and bytes: LCP, CLS, TBT, TTFB, JavaScript, CSS, fonts, images, caching and compression, measured as the median of several runs on a throttled mobile and a desktop profile. - `lcp-background-image` LCP element is a CSS background image — [perf/lcp-background-image](https://void-design.vercel.app/rules/perf/lcp-background-image) - `image-oversized` Image is much larger than its rendered size — [perf/image-oversized](https://void-design.vercel.app/rules/perf/image-oversized) - `image-legacy-format` Image served in a legacy format — [perf/image-legacy-format](https://void-design.vercel.app/rules/perf/image-legacy-format) - `images-missing-dimensions` Images without width/height or aspect-ratio — [perf/images-missing-dimensions](https://void-design.vercel.app/rules/perf/images-missing-dimensions) - `no-text-compression` Text resources are served uncompressed — [perf/no-text-compression](https://void-design.vercel.app/rules/perf/no-text-compression) - `cache-headers` Hashed static assets are not cached long-term — [perf/cache-headers](https://void-design.vercel.app/rules/perf/cache-headers) - `third-party-heavy` Heavy third-party footprint — [perf/third-party-heavy](https://void-design.vercel.app/rules/perf/third-party-heavy) - `dom-size` DOM is very large — [perf/dom-size](https://void-design.vercel.app/rules/perf/dom-size) Detected by `void perf` and `void audit`. Explain it in a terminal: `void rules perf/render-blocking`