Use automated tools like PurgeCSS or UnCSS to scan and remove unused CSS; 2. Integrate purging into your build process via Webpack, Vite, or Tailwind’s content configuration; 3. Audit CSS usage with Chrome DevTools Coverage tab before purging to avoid removing needed styles; 4. Safelist dynamically generated or conditionally used classes to prevent accidental removal; 5. Alternatively, extract critical CSS and lazy-load the rest using tools like critical or Penthouse—always test after purging to ensure functionality remains intact.
Purging unused CSS helps reduce file size, improve page load speed, and streamline your production code. Here’s how to do it effectively.
1. Use a CSS Purge Tool (Recommended)
The most reliable way is to use automated tools that scan your HTML, JavaScript, or template files and remove CSS rules that aren’t being used.
Popular Tools:
- PurgeCSS – Works with build tools like Webpack, Vite, Rollup, or standalone.
- UnCSS – Great for static sites or when using Node.js.
-
PurgeCSS with Tailwind CSS – Built-in via
contentarray intailwind.config.js.
Example with PurgeCSS in a project:
// purgecss.config.js
module.exports = {
content: ['./src/**/*.html', './src/**/*.js'],
css: ['./src/**/*.css'],
output: './dist/purged/',
rejected: true, // see what was removed
};Run it via CLI or integrate into your build script.
2. Integrate with Your Build Process
To make purging part of your workflow:
For Tailwind users:
Ensurepurgeorcontentis set in config:// tailwind.config.js module.exports = { content: [ './src/**/*.{html,js,jsx,ts,tsx}', ], theme: { ... }, plugins: [], }Then build with
NODE_ENV=productionso Tailwind automatically purges.With Webpack: Use
PurgeCSSPlugin:const PurgeCSSPlugin = require('purgecss-webpack-plugin'); const glob = require('glob'); const path = require('path'); plugins: [ new PurgeCSSPlugin({ paths: glob.sync(path.join(__dirname, 'src/**/*.{js,html}')), }), ]
3. Audit First, Then Purge
Before removing anything, audit your CSS usage:
- Use Chrome DevTools Coverage tab (
Ctrl Shift P→ "Coverage") to see unused CSS on a page. - Identify large, unused chunks.
- Manually remove or refactor styles based on findings.
This helps avoid over-purging (e.g., dynamically injected classes or JS-dependent styles).
4. Be Cautious with Dynamic Classes
Purging tools can’t always detect:
- Classes generated dynamically in JavaScript.
- Utility classes used conditionally (e.g.,
hidden,active,show-modal). - Framework-specific patterns (React, Vue, etc.).
Solutions:
- Whitelist critical classes:
// purgecss.config.js defaultExtractor: content => content.match(/[\w-/:] (?<!:)/g) || [], safelist: ['opacity-0', 'translate-y-full', 'delay-300', 'lg:col-span-2'],
- Test thoroughly after purging.
- Tools:
critical,Penthouse, or online generators. - Inline critical CSS, load full stylesheet asynchronously.
5. Alternative: Use Critical CSS Lazy Load
Instead of purging globally, extract critical CSS (above-the-fold styles) and lazy-load the rest:
This reduces render-blocking resources without removing styles entirely.
Purging unused CSS isn’t just about size — it’s about performance and maintainability. Use tools like PurgeCSS or rely on framework-level optimization (like Tailwind), but always test in real user scenarios.
Basically: scan, purge, verify. Not complex — but easy to mess up if you skip testing.
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