CSS Validator

The CSS Validator is a browser-based tool that analyzes your stylesheet code and identifies syntax errors, invalid property values, malformed rules, and common structural issues. Whether you are debugging a broken layout or reviewing code before deployment, this tool gives you immediate, clear feedback on what is wrong and where — without needing to install any local tooling or configure a build pipeline.

Clean, valid CSS is essential for predictable rendering across browsers. Even a single missing semicolon or an unrecognized property value can silently break styles in ways that are difficult to trace. This validator helps you catch those issues early, making it especially valuable during development, code review, or when integrating third-party CSS into an existing project.

To use the CSS Validator, paste your stylesheet code directly into the input area and run the validation. The tool parses your CSS and returns a structured report highlighting any errors or warnings, along with the line number and a description of each issue. Errors indicate invalid syntax that browsers may reject or handle inconsistently, while warnings flag practices that are technically valid but potentially problematic.

The validator handles standard CSS including media queries, custom properties (CSS variables), keyframe animations, and pseudo-selectors. It is designed to work with plain CSS files — if you are working with preprocessor syntax such as SCSS or Less, you will need to compile it to standard CSS first before validating.

Keep in mind that vendor-prefixed properties (such as -webkit- or -moz-) may be flagged as warnings depending on the validation rules in use. These are often intentional and safe to ignore. Focus on errors first, as those represent genuine syntax problems that could affect how your styles are rendered across different browsers and environments.