CSS Minifier

Minified or gzipped — which number matters?

Every CSS minifier reports raw bytes saved, and no browser has ever downloaded raw bytes — real transport runs through gzip or brotli first. Measured on Bootstrap 5.3.3's CSS: minifying alone takes 281,046 bytes down to 232,803, a 17.2% raw saving. Once gzip runs on both files, the gap narrows to 33,308 versus 30,829 bytes — a 7.4% saving. Gzip was already eating most of the redundancy that whitespace and comments represent, because whitespace compresses extremely well on its own. For a CSS file the size question is not "how much smaller is the raw file" but "how much smaller does it arrive" — and this tool's Size tab answers the second one, measured in your own browser with CompressionStream, never estimated.

What this minifier will not do to your file

Measured on 2026-09-10 against a fixture containing .e{ &:hover{ color:blue }}: clean-css 5, csso 4 and the Toptal cssminifier API (the top-ranking result for "css minifier") all delete the rule entirely. HTTP 200, no warning, no error — a block of styling simply disappears. CSS Nesting reached every target browser in 2023 and is now ordinary in hand-written CSS, so this is not an edge case; it is what happens to any stylesheet using the syntax you would naturally reach for today. This tool's parser is nesting-native from the ground up: a rule's block may contain nested rules and nested at-rules at any depth, because that is what the spec actually allows.

The same fixture set catches two more failure modes worth knowing about. A custom property's value — --x: 0.50s — is a token stream substituted verbatim by var(); one popular engine rewrites the inside of a custom property block, which changes a value a script or a @property registration may be reading by exact text. This tool trims only leading and trailing whitespace on a custom property and never touches anything else. And browser hacks — *zoom:1, _height, color:red\9 — are invalid CSS that specific old browsers intentionally honour; one engine drops them, another keeps them inconsistently. This tool keeps every hack by default and lists what it found, so removing one is a choice you make, not one made for you.

Minification is not obfuscation

Minified CSS is trivially beautified back — this page's own Beautify mode does exactly that — so it provides no secrecy for a design system or a paid theme. It is also not compression: gzip and brotli do the actual byte-shrinking work at transport time, and minifying mostly removes the redundancy gzip would otherwise have compressed for you (see the gzip section above). What minifying genuinely buys you is a smaller file before compression even starts, which matters most for CSS that is already dense with data URIs or long class names that gzip handles less efficiently.

Common use cases

• Shrinking a stylesheet before shipping it, while keeping licence notices intact
• Checking whether minifying a particular file is worth the risk once gzip runs
• Reading a minified third-party stylesheet by beautifying it first
• Confirming a nested rule or browser hack survived a build step unchanged
• Seeing which option — comments, whitespace, colour shortening — earned which bytes