CSS Minifier

This tool uses CSSO (CSS Optimizer) which goes beyond simple whitespace removal — it can merge duplicate rules, shorten color values (e.g. #ffffff to #fff), and remove redundant properties while keeping the visual output identical. The result is the smallest valid CSS that produces the same rendering in every browser.

Smaller stylesheets mean faster page loads, lower bandwidth costs, and quicker time-to-first-paint. Even a 20-30% reduction in CSS size can noticeably improve performance on mobile connections where every kilobyte counts.

CSSO operates in two phases. First, it strips all non-essential characters: whitespace between tokens, comments, trailing semicolons, and unnecessary quotes around font names. Second, it performs structural optimization — merging adjacent rules with identical selectors, combining declarations that appear in multiple rules, and shortening values where safe (0px becomes 0, #aabbcc becomes #abc).

The structural phase is where CSSO differs from simpler minifiers. It understands CSS specificity and cascade rules well enough to merge selectors without changing the visual outcome. However, if your stylesheet depends on a specific declaration order for overrides between selectors of equal specificity, CSSO's merging could theoretically reorder them — though it is conservative and avoids merges where order might matter.

The minification runs entirely in your browser — your CSS is never sent to any server. There is no backend, no upload step, and no logging of your input. This makes the tool safe for proprietary design systems, internal stylesheets, or any CSS you would not want leaving your machine.

CSS0 is loaded as a JavaScript module that executes locally in your browser's main thread. When you close or refresh the tab, any pasted content is gone with no trace.

Comments are always stripped during minification — if you have license headers or source annotations in your CSS, save them separately before minifying. CSSO will also remove duplicate properties within a single rule, keeping only the last one (which matches how browsers resolve duplicates).

If your CSS uses intentional duplicate properties as a fallback pattern (e.g. color: red; color: var(--accent) for browsers that do not support custom properties), the minifier preserves both because they have different values. Be cautious with specificity-dependent ordering: while CSSO is conservative about merging, testing the minified output in your target browsers is always good practice for complex stylesheets.