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CSS Validator

開発者文章

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入力

自動処理

出力

クライアント側

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ガイド

CSS Validator

The CSS Validator checks your CSS stylesheets for syntax errors, invalid properties, and W3C compliance issues. Paste your CSS code and get instant feedback with detailed error messages, line numbers, and warnings to help you write clean, standards-compliant stylesheets.

使い方

Paste or type your CSS code into the input area. The validator automatically analyzes your stylesheet and displays results in real time. Errors appear with red indicators showing the exact line and column number, while warnings for invalid property values are highlighted in yellow. Click “Try an example” to load sample CSS and see how the validator works.

特徴

リアルタイム検証 – CSS is validated as you type with instant feedback
Syntax Error Detection – Catches missing semicolons, unclosed brackets, and malformed rules
Property Value Validation – Checks that CSS property values match W3C specifications
Line & Column Numbers – Pinpoints the exact location of each issue in your code
クライアント側処理 – All validation happens in your browser, no data is sent to any server

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 よくある質問

What is CSS validation and why does it matter?

CSS validation is the process of checking stylesheets against the W3C CSS specification to ensure they follow the official syntax rules. Valid CSS helps prevent rendering inconsistencies across browsers, improves page load performance by avoiding error recovery overhead, and makes stylesheets easier to maintain.
What are the most common CSS syntax errors?

The most frequent CSS errors include missing semicolons at the end of declarations, unclosed curly braces in rule blocks, typos in property names like backgroud instead of background, and invalid values such as using px units with unitless properties. Nested comments and malformed media queries are also common issues.
What is the difference between CSS errors and warnings?

CSS errors indicate syntax problems that prevent the browser from parsing a rule correctly, such as missing brackets or invalid selectors. Warnings typically flag valid syntax that uses non-standard or deprecated property values. Browsers may still render warned properties but behavior could vary across implementations.
Does minified CSS affect validation results?

No, CSS validation checks syntax and property correctness regardless of formatting. Minified CSS that was valid before minification will still pass validation. However, poorly minified CSS where semicolons or braces were incorrectly removed will produce errors, which helps catch broken build tool output.