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CSS Formatter + Validator — Beautify, Minify, and Check CSS Online Free
Paste your CSS to format, minify, or check for syntax errors. Server-side processing — no files stored, no signup required. Handles CSS3 including Grid, Flexbox, and modern property syntax.
Processed on our server — your CSS is never stored or logged.
About CSS Formatter + Validator
CSS Formatter + Validator gives you three tools in one interface for handling CSS code. Paste a stylesheet or upload a .css file and choose a mode: Format to produce clean, readable CSS; Minify to strip all whitespace for production; Validate to find syntax errors with exact line and column numbers. Processing happens on the server — nothing is stored or logged.
Format mode
Format mode pretty-prints any CSS — including minified production CSS or hand-written code with inconsistent spacing — into clean 2-space-indented output. Each rule block gets its own line. Each property declaration sits on its own indented line. Opening braces sit on the same line as the selector. This is the standard style used by major CSS editors, Prettier, and most style guides. If you inherited a minified stylesheet and need to read it or audit it before editing, Format mode is the first step.
Minify mode
Minify mode removes all comments, whitespace, and unnecessary characters from your CSS. It also collapses shorthand properties where possible — turning margin: 0 0 0 0 into margin: 0 — and shortens six-character hex colors to three characters where the format allows (#ffffff → #fff). The output is the smallest valid CSS string that is functionally identical to the input. A stats line below the output shows the input size, output size, and percentage reduction so you can confirm the savings before replacing your production file.
Validate mode
Validate mode parses your CSS using a PHP CSS parser and returns a list of any syntax errors found, each with the exact line number, column number, and a description of the problem. Common errors include unclosed braces, unknown at-rules, invalid property values, and missing semicolons. The validator supports CSS3 including Grid, Flexbox, custom properties (CSS variables), media queries, and keyframe animation syntax. If the CSS is valid, the result shows a "No issues found" confirmation.
What it handles
All three modes support standard CSS3 syntax: selectors (element, class, ID, attribute, pseudo-class, pseudo-element, combinators), properties and values including shorthand, at-rules (@media, @keyframes, @import, @charset, @supports, @font-face), custom properties (--var-name), and calc/clamp/min/max functions. Pre-processor syntax (Sass/SCSS/Less/Stylus) is not supported — run the file through your pre-processor first and paste the compiled CSS output.
Common use cases
- Reading minified production CSS — A frontend developer is debugging a visual regression and needs to read the production stylesheet. The compiled bundle is one line of minified CSS. Paste it here in Format mode and the indented output makes the rule structure and property values immediately readable.
- Compressing CSS before deployment — A developer has finished editing a hand-formatted stylesheet and wants to minify it before checking it into the build output. Paste the readable CSS here, switch to Minify, confirm the reduction percentage in the stats bar, and copy the output directly into the dist file.
- Catching syntax errors before push — A developer adds a new @keyframes block to a stylesheet and a browser shows an unexpected rendering bug. Paste the stylesheet in Validate mode — the validator pinpoints a missing closing brace at the exact line where the error occurred, resolving the issue in seconds.
- Validating CSS Grid and Flexbox layouts — A designer is hand-writing a Grid layout with complex area definitions and wants to confirm the syntax is valid before testing in browsers. Validate mode checks the grid-template-areas, grid-template-columns, and gap values against the CSS3 spec and reports any property name typos or value format errors.
- Cleaning up copy-pasted snippet CSS — A developer copies a CSS snippet from a documentation site and pastes it into a project. The snippet has browser-prefixed properties with inconsistent indentation and vendor-prefix ordering. Format mode normalises the indentation; Validate mode confirms the snippet has no syntax errors before integrating it into the main stylesheet.
Frequently asked questions
What does a CSS formatter do?
A CSS formatter takes CSS that is minified or inconsistently indented and outputs it with consistent 2-space indentation — one property declaration per line, opening braces on the selector line, closing braces on their own line. This makes the stylesheet easy to read, diff, and edit.
Is my CSS sent to a server?
Yes. All three modes — Format, Minify, and Validate — process your CSS on the server using a PHP CSS parser. Your stylesheet is sent over HTTPS and discarded immediately after processing. Nothing is written to disk or retained between requests.
Does CSS minification change how the page looks?
No. Minification removes characters that have no effect on rendering: whitespace between tokens, comments, and redundant syntax. The browser interprets minified and formatted CSS identically. The only exception is if your code relies on whitespace-sensitive CSS tricks — those are rare edge cases.
Does the validator support CSS custom properties (variables)?
Yes. Custom properties (--variable-name: value) are valid CSS3 syntax and are parsed correctly in Validate mode. If a custom property declaration has a syntax error, the validator reports the line and column.
Can I validate SCSS or Sass?
No. This tool validates standard CSS3 only. SCSS and Sass use pre-processor syntax (nesting, variables with $, mixins) that is not valid CSS3. Run your Sass/SCSS through its compiler first, then paste the compiled CSS output here.
Does this work for CSS Grid and Flexbox?
Yes. CSS Grid and Flexbox use standard CSS property syntax — display: grid, grid-template-columns, flex, align-items, and so on. These are fully valid CSS3 and are formatted, minified, and validated correctly by this tool.
What is the maximum input size?
The maximum input size is 500 KB, which is larger than any normal stylesheet. If you receive a size error, the most likely cause is that you pasted the entire output of a CSS bundler that inlines all dependencies.
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