CSS minifier

Reembun. (2026, July 28). CSS minifier. https://reembun.com/css-minifier

What it removes

• Comments, except licence banners beginning /*!
• Whitespace, collapsed to a single space and dropped where syntactically unnecessary
• Redundant semicolons, including the last one before a closing brace

What it deliberately does not do

Aggressive minifiers also reorder declarations, merge rules, rewrite shorthand and re-encode colours. Each of those can change behaviour:

• Reordering declarations breaks the cascade when a longhand follows a shorthand
• Merging rules changes specificity resolution in edge cases
• Rewriting shorthand can drop an implicit value that a later rule relied on
• Re-encoding colours is safe until it meets a colour in a format the tool guessed wrong about

None of those are done here. Everything removed is whitespace, comments or syntactically redundant punctuation.

The cases regex minifiers fail

A regex-based minifier cannot tell whether a { is structure or content. All of these are valid CSS and all break naive tools:

a { content: "/*"; }        /* a comment marker inside a string */
a { content: "}"; }          /* a brace inside a string */
a { content: "a;b"; }        /* a semicolon inside a string */
a { background: url(data:image/svg+xml;base64,AAA); }

This minifier is a character scanner that tracks state, so strings and url() values pass through untouched.

Where whitespace can and cannot be dropped

The rules are asymmetric, and getting them wrong produces CSS that silently stops matching:

Context	Space	Reason
@media (min-width:1px)	Required before (	At-rule syntax
@media (a) and (b)	Required after )	Separates the query
a [href]	Required before [	Descendant combinator
[a] [b]	Required after ]	Descendant combinator
calc(1px + 2px)	Required around +	calc grammar
.a > .b	Droppable	Child combinator
h1 , h2	Droppable	Selector list

So an opening bracket licenses dropping only the space that follows it, and a closing bracket only the space that precedes it.

How much it saves

Input	Typical reduction
Hand-written CSS with comments	25-40%
Already-formatted framework output	15-25%
Previously minified	Under 2%

Over HTTP with gzip or brotli, most of that saving disappears, since compression handles repeated whitespace very well. Minification still matters for the uncompressed size a browser has to parse, and for anything embedded inline in a page.

Beautifying

The beautifier normalises through the minifier first, then re-indents. That means it produces consistent output regardless of how the input was formatted, and round-tripping beautify then minify returns exactly the original minified form.