Unused CSS refers to CSS rules and selectors that are loaded by the browser but never applied to any element on the page. A selector like .hero-button is unused if no element with that class exists in the HTML. Unused CSS increases CSS file size, adds to render-blocking resource weight, and slows First Contentful Paint.

How do I find unused CSS?

The fastest ways to find unused CSS: (1) This tool — paste HTML and CSS to get instant results. (2) Chrome DevTools Coverage tab (F12 → More tools → Coverage) — shows % of CSS used during page load. (3) PurgeCSS or UnusedCSS.com for automated removal from full codebases. (4) The Lighthouse audit in Chrome DevTools flags unused CSS under 'Reduce unused CSS'.

Unused CSS Finder – Find & Remove Unused CSS Online

How to Find and Remove Unused CSS

Multiple approaches to identifying and removing unused CSS — from this tool for quick checks to automated pipeline solutions.

Using this tool

Paste your HTML source in the left pane and your CSS in the right pane. Click Analyze. The tool parses every selector from the CSS and checks whether it could match any element in the HTML. Unused selectors are listed with their approximate byte cost. Download the cleaned CSS directly or copy it to clipboard.

For best results: include the full page HTML (not a partial), and paste all CSS files concatenated into the CSS pane. The tool handles class selectors (.btn), ID selectors (#nav), element selectors (h1), and attribute selectors ([type="text"]).

Chrome DevTools Coverage

For live sites: open Chrome DevTools (F12) → click the three-dot menu → More Tools → Coverage. Click the record button and interact with your page. The Coverage tab shows the exact % of each CSS file that was used during your session. This is the most accurate method since it measures actual runtime usage including dynamic JavaScript-injected classes.

PurgeCSS (automated)

PurgeCSS is a Node.js tool that analyzes HTML, JS, and template files to remove unused CSS from your build output. It integrates with Webpack, Vite, and PostCSS. Ideal for production builds — eliminates unused CSS from Tailwind, Bootstrap, or any CSS framework before deployment. Run as part of your CI/CD pipeline for zero-unused-CSS production builds.

What this tool can't detect

No static analyzer can catch: CSS classes added dynamically by JavaScript at runtime (e.g., classList.add('active')), pseudo-classes like :hover and :focus (considered used if the base selector matches), @keyframes used by animations, or media-query-scoped styles that only apply at certain screen widths. Always manually review results before deleting CSS in production.

Unused CSS Tools Comparison

The main tools for finding and removing unused CSS — choose based on your workflow.

Tool	Type	Detects JS Classes	Requires Install	Cost	Best For
This Tool	Browser (paste)	❌ Static only	No	Free	Quick single-page check
Chrome Coverage	Browser DevTools	✅ Yes (runtime)	No (built-in)	Free	Accurate live analysis
PurgeCSS	CLI / Build plugin	✅ With config	npm install	Free	Production builds, CI/CD
UnusedCSS.com	SaaS (URL crawl)	✅ Yes (rendering)	No	Free/Paid	Full site audits
VS Code Extension	IDE	⚠️ Partial	VS Code	Free	Real-time editing
Lighthouse	Browser audit	✅ Yes (rendering)	No (built-in)	Free	Core Web Vitals audit

Unused CSS Finder – FAQ

What is unused CSS?+

Unused CSS refers to CSS rules and selectors loaded by the browser but never applied to any element on the page. A selector like .promo-banner is unused if no element with that class exists in the HTML. Unused CSS increases CSS file size, adds render-blocking weight, and slows First Contentful Paint. Typical production sites have 40-60% unused CSS from frameworks like Bootstrap or Tailwind when not purged.

How does this unused CSS finder work?+

The tool parses the CSS input to extract every selector using a regex-based CSS parser. It then checks each selector against the HTML to see if any matching elements exist. For class selectors (.btn), it checks for class="btn" in the HTML. For ID selectors (#nav), it checks for id="nav". For element selectors (h1), it checks for the tag. Selectors with no match in the HTML are flagged as unused. The clean CSS output contains only the rules whose selectors matched.

Does unused CSS affect Core Web Vitals?+

Yes. Unused CSS increases the size of render-blocking resources. CSS is render-blocking by default — the browser won't render the page until all CSS is downloaded and parsed. Larger CSS files mean longer First Contentful Paint (FCP) and Largest Contentful Paint (LCP). Google Lighthouse includes "Reduce unused CSS" as a performance opportunity, and it directly impacts LCP which is a Core Web Vitals metric. Removing unused CSS from a typical site can save 50-150KB and meaningfully improve FCP.

Will removing detected unused CSS break my site?+

Static analysis can miss CSS that's added dynamically by JavaScript (classList.add, third-party scripts, state classes). Always: (1) test on a staging environment first, (2) keep CSS for interactive states (:hover, :focus, :active), (3) keep CSS for dynamically added classes your JS uses, and (4) back up your original CSS before replacing it. For maximum safety, use Chrome DevTools Coverage tab after interacting with all page states — it catches runtime-added classes that static analysis misses.

What is the best tool to remove unused CSS in production?+

For production builds: PurgeCSS integrated into your Vite or Webpack build pipeline is the gold standard. It scans all HTML, JS, and template files to find CSS classes in use and removes everything else. For Tailwind CSS specifically, Tailwind's built-in JIT engine eliminates unused styles automatically. For quick one-off checks of a single page: this tool or Chrome DevTools Coverage. For full site audits: UnusedCSS.com crawls your live site and renders it to detect runtime classes.

Unused CSS Finder
Find & Remove Unused CSS Online