Code Quality · Free CSS tool

Duplicate CSS Remover

Free · no sign-up Live preview · copy or download the CSS

Copy-paste debt, resolved: rules sharing the same selector get merged into one, and repeated declarations inside a rule collapse to the last occurrence (matching how the cascade already resolved them) — with a report of everything that changed.

Settings

Results appear here.
Generated CSS — updates live


The CSS you need to build this yourself
Understand the output, not just copy it — these lessons on our learning path teach exactly what this tool automates:
STEP 1 · 20 minCSS Syntax & SelectorsRules and the cascade order.STEP 2 · 25 minCSS Specificity & ArchitectureWhy last-wins is the law.STEP 3 · 15 minHow to Add CSSKeeping one source of truth.


  1. CSS Analyzer & Stylesheet StatsAnalyzers
  2. CSS Property SorterCode Quality
  3. Unused CSS FinderAnalyzers
  4. CSS Minifier & FormatterDeveloper Tools
  5. CSS Diff CheckerCode Quality


How it works


Two passes: first, rules with identical selectors merge into one (declaration lists concatenated in order); second, within each merged rule, repeated properties collapse to their last value — exactly the value the browser was already using, so the visual result is unchanged while the noise disappears.


One honest caveat, also shown in the results: progressive-enhancement pairs (width: 90% then width: min(90%, 60ch)) are deliberate duplicates for older browsers. The tool can't read intent — restore those pairs if you use the pattern.


Run the code — try it yourself
This stylesheet declares .box twice and background twice. Merge by hand into one clean rule — then verify against the tool.


exercise.html — editable


Frequently asked questions
Why does selector merging matter beyond tidiness?
Scattered halves of a rule are how contradictory edits happen — someone updates one .card block, not the other. One selector, one home.
Does it merge .card and .card:hover?
No — different selectors are different rules by definition. Only exact selector matches merge.
Media queries?
Rules inside @media are currently passed through untouched — dedupe applies to top-level rules, keeping conditional overrides safe.


Keep going
Duplication is entropy in stylesheet form. Prevent the next round with sorted properties (Property Sorter makes duplicates jump out in diffs) and the architecture habits in Specificity & Architecture.
CSSmatic is a non-profit project, made by developers for developers.