🌐
W3C
jigsaw.w3.org › css-validator
The W3C CSS Validation Service
Check Cascading Style Sheets (CSS) and (X)HTML documents with style sheets ... Note: If you want to validate your CSS style sheet embedded in an (X)HTML document, you should first check that the (X)HTML you use is valid.
validator service by the World Wide Web Consortium
The Markup Validation Service is a validator by the World Wide Web Consortium (W3C) that allows Internet users to check pre-HTML5 HTML and XHTML documents for well-formed markup against a document type … Wikipedia
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W3C
validator.w3.org
The W3C Markup Validation Service
Note: file upload may not work ... information page on the W3C QA Website. ... This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc. If you wish to validate specific content such as RSS/Atom feeds or CSS stylesheets, MobileOK content, ...
Discussions

Recommendations for a CSS validator? The W3C validator appears to be outdated.
Support seems to be .....not great ? https://caniuse.com/?search=nested%20selector More on reddit.com
🌐 r/webdev
7
6
November 23, 2023
CSS 2.2: Where to validate it? And why W3C validator provides an option to validate 2.1 but not 2.2?
Skip online validation, it's so far behind at this point that you're not going to see much value from it. Heck, Chrome does a solid job of warning you at this point. Instead use Stylelint just as you would use ESLint for JavaScript. You should also be using Prettier to make sure your code is formatted appropriately. More on reddit.com
🌐 r/css
2
1
June 16, 2024
validation - Differences between validator.w3.org and jigsaw.w3.org css validator? - Stack Overflow
I tested both css validators to test my css3 document. The jigsaw.w3.org validator pass my document with zero errors, but the validator.w3.org find a lot of errors. Some of these errors are related... More on stackoverflow.com
🌐 stackoverflow.com
seo - Should I ignore W3 CSS Validation Service? - Webmasters Stack Exchange
I just checked my site with W3 CSS Validation Service. It had more than 200 errors. Then I checked many sites including Stack OverFlow. Here is the results of Stack OverFlow. SO also has 108 erro... More on webmasters.stackexchange.com
🌐 webmasters.stackexchange.com
September 25, 2017
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W3Schools
w3schools.com › w3css › w3css_validation.asp
W3.CSS Validation
The W3C CSS Validator checks for CSS1, CSS2, CSS3, and CSS4 properties.
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GitHub
github.com › w3c › css-validator
GitHub - w3c/css-validator: W3C CSS Validation Service · GitHub
W3C CSS Validation Service. Contribute to w3c/css-validator development by creating an account on GitHub.
Starred by 234 users
Forked by 115 users
Languages   Java 77.5% | HTML 16.1% | Emacs Lisp 1.2% | Ruby 1.1% | JavaScript 1.1% | SystemVerilog 0.9%
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Webmaster World
webmasterworld.com › css › 5003357.htm
The W3C CSS Validation Service - CSS forum at WebmasterWorld - WebmasterWorld
There is a nu validator that you can try and it may offer a better explanation of any errors or warnings - it is set up to validate .html, .css and/or .svg files. Select the level of report you want to see: [validator.w3.org...] You can read more about any of the terms or elements you are having errors with, though be prepared to open a dozen tabs for any given element as it refers to so many documents that go into increasingly convoluted detail.
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Css-validator
css-validator.org
CSS Validation Service
This only irritates the visitor and he browses to some other website from where he can access info with out any delay. This decreases the volume of visitors on your website. W3C CSS takes care of this issue. It also provides an attractive visual display.
Find elsewhere
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W3C
w3.org › wiki › CssValidator
CssValidator - W3C Wiki
The CSS Validator is a free software developed by W3C, and a free online service .
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Reddit
reddit.com › r/webdev › recommendations for a css validator? the w3c validator appears to be outdated.
r/webdev on Reddit: Recommendations for a CSS validator? The W3C validator appears to be outdated.
November 23, 2023 -

My old standby, the W3C Validator, appears to be a bit out-of-date and doesn't support nested selectors.

I tried the csstree validator but it stops working when input contains CSS variables (e.g. --color: green).

I also tried the csstree-validator NPM package but it's choking on nested @media rules, which are a fairly recent addition.

What I'm really hoping for is an NPM package that can validate the CSS compiled by a static site generator, but even just something I could copy-paste into would be fine.

Any recommendations?

Edit: Actually, Stylelint seems like it'll do just fine, with the added advantage that we already use it in our projects for linting!

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CSS Validator
codebeautify.org › cssvalidate
W3 CSS Validator Online to validate CSS
This tool helps to validate CSS based on W3 CSS rules, show errors, and suggestion to write the correct CSS.
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Devzery
devzery.com › post › w3-website-validator-guide-to-html-and-css-validation
W3 Website Validator: Guide to HTML and CSS Validation
September 16, 2024 - Learn how to use the W3 Website Validator for error-free HTML and CSS. Improve your site's SEO, performance, and user experience.
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W3C
validator.w3.org › services
W3C Validation Services
User-Agent: Validator.nu/LV · About · Service · User-Agent: W3C-checklink · About · * as a crawling service this honors robots.txt directives · Service · User-Agent: W3C_I18n-Checker/1.0 · About · Service · User-Agent: FeedValidator/1.3 · About · Service · User-Agent: Jigsaw/2.3.0 W3C_CSS_Validator_JFouffa/2.0 ·
🌐
Chrome Web Store
chromewebstore.google.com › detail › css-validator › hhlcpmdhlcoghhfgiiopcjbkfmdliknc
CSS validator - Chrome Web Store
November 19, 2024 - CSS Validator is here to make your life easier and your project cleaner. 🌟 Key Highlights ▸ Validates W3C compliance ▸ Checks stylesheets for errors ▸ Offers CSS linting ▸ Enhances website validity 🚀 Enhance Your Coding Today Transform ...
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Reddit
reddit.com › r/css › css 2.2: where to validate it? and why w3c validator provides an option to validate 2.1 but not 2.2?
r/css on Reddit: CSS 2.2: Where to validate it? And why W3C validator provides an option to validate 2.1 but not 2.2?
June 16, 2024 -

There are two questions here. I hope at least the second one is not off-topic for Stack Overflow.

The second question is very short:

  • Where can I validate CSS 2.2?

The first question is longer.

Could anybody explain why CSS 2.2, compared to 2.1, feels like a "second-class citizen"? For example,

  • the Wikipedia article about CSS mentions CSS 2.1 fifteen times, whereas CSS 2.2 only once

  • https://css-validator.org/ and https://jigsaw.w3.org/css-validator/ provides an option to validate 2.1, but not 2.2

According to this: https://github.com/w3c/csswg-drafts/issues/2008 discussion, CSS 2.2 is merely 2.1 with incorporated errata, but this doesn't answer why 2.2 didn't gain any traceable, on the Web, mentions.

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npm
npmjs.com › package › w3c-css-validator
w3c-css-validator - npm
A modern package for validating CSS using W3C’s public CSS validator service.
      » npm install w3c-css-validator
    
Published   Dec 02, 2025
Version   1.4.1
Author   Sparksuite
🌐
Mozilla Support
support.mozilla.org › en-US › questions › 1278165
Anyone else find the W3C validator won't load? | Firefox Support Forum | Mozilla Support
January 24, 2020 - http://validator.w3.org/ renders as a blank page. Same for https://jigsaw.w3.org/css-validator/. Switching to basic page style, I can get to the unstyled content of the page, but why aren't the styles loading?
🌐
Minifier
minifier.org › css-validator
CSS Validator / CSS Code Checker
CSS checker helps find and fix issues in CSS and ensures code follows the rules set by the World Wide Web Consortium and does not contain any syntax errors or other issues. Validate your CSS files with our free CSS code checker.
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CSS Portal
cssportal.com › css-validator
CSS Validator - CSS Portal
Syntax Checking: CSS validators check for syntax errors in your CSS code. They ensure that you have used the correct syntax for CSS properties, values, and selectors. Compliance with Standards: They verify that your CSS code complies with the ...
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Visual Studio Marketplace
marketplace.visualstudio.com › items
W3C Web Validator - Visual Studio Marketplace
Extension for Visual Studio Code - Check the validity of your HTML/CSS files in one click