Critical CSS Generator
Free Critical CSS Generator that extracts CSS rules used by above-the-fold HTML to improve first paint and Core Web Vitals. 100% client-side.
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What is Critical CSS Generator?
A Critical CSS Generator identifies stylesheet rules that match the HTML visible during the first page view. By extracting these above-the-fold styles, developers can inline a smaller CSS payload and let the remaining stylesheet load later. This browser-based tool uses a lightweight selector heuristic and never uploads your source.
Key Benefits
- Prioritize styles needed for the first render
- Reduce render-blocking CSS during initial navigation
- Inspect selector usage against real HTML markup
- Copy or download a ready-to-review critical.css file
- Keep source code private with local browser processing
Common Use Cases
- •Improving Lighthouse and Core Web Vitals experiments
- •Preparing inline CSS for static websites and landing pages
- •Auditing which selectors are used above the fold
- •Creating a starting point for a production critical CSS pipeline
How to Extract Critical CSS
- Paste above-the-fold HTML: Enter the HTML structure that should render during the initial page view.
- Paste the stylesheet: Add the page CSS, including the selectors used by the pasted HTML.
- Extract matching rules: Click Extract Critical CSS to match tags, classes, IDs, and root styles.
- Copy or download: Review the result, then copy it or download it as critical.css for your performance workflow.
Key Features
- Matches HTML tags, classes, IDs, root styles, and universal selectors.
- Extracts rules from a full pasted stylesheet without uploading source code.
- Keeps charset and import directives when they appear at the top of the stylesheet.
- Displays a formatted critical.css result with the number of matched rules.
- Copy the result or download it directly as a CSS file.
- Runs offline in the browser with no API or build step required.
Frequently Asked Questions
What is critical CSS?
Critical CSS is the minimum set of styles needed to render the visible part of a page. Loading it first can reduce render-blocking work and improve perceived page speed.
How does this Critical CSS Generator work?
It reads the HTML tags, classes, and IDs you paste, then keeps stylesheet rules whose selectors match those signals. Root, body, html, and universal rules are also included.
Does this tool upload my HTML or CSS?
No. The extraction runs entirely in your browser, so source code remains on your device and no API request is required.
Is the output safe to use in production?
Treat the output as a helpful starting point. This lightweight heuristic does not evaluate JavaScript state, responsive viewport changes, pseudo-elements, or every nested at-rule, so review it and test your page before deployment.