Chrome Web Store
chromewebstore.google.com › detail › w3c-markup-validation-ser › kfjemflfclknofbklcnbnpjelkfhcomk
W3C Markup Validation Service for CSR pages - Chrome Web Store
Use W3C html validator online to validate html for errors and syntax issues.
W3C
validator.w3.org
The W3C Markup Validation Service
Check the markup (HTML, XHTML, ... Pack 2, see our information page on the W3C QA Website. ... This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc....
Videos
06:19
How to use W3C HTML and CSS code validators - YouTube
How To Validate Your HTML5 Code Using An Online Validation Service ...
05:55
Using the W3C validator to check HTML - YouTube
02:14
Installing the HTML Validator in Chrome - YouTube
06:57
Validate HTML5 code using Google Chrome HTML Validator - YouTube
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
Visual Studio Marketplace
marketplace.visualstudio.com › items
W3C Offline HTML Validator - Visual Studio Marketplace
Extension for Visual Studio Code - A VSCode extension for offline HTML validation using W3C standards.
Visual Studio Marketplace
marketplace.visualstudio.com › items
W3C Validation - Visual Studio Marketplace
Extension for Visual Studio Code - Adds W3C validation support to Visual Studio Code.
W3C
validator.w3.org › nu
Ready to check - Nu Html Checker
This tool is an ongoing experiment in better HTML checking, and its behavior remains subject to change · Show sourceoutlineimage reporterrors & warnings onlycheck error pagesUser-Agent Accept-Language
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.
W3C
w3.org › developers › tools
Validators and tools | Developers | W3C
This page lists the validators and web developer tools.
Chrome Web Store
chrome.google.com › webstore › detail › html-validator › mpbelhhnfhfjnaehkcnnaknldmnocglk
HTML Validator - Chrome Web Store
HTML Validator for Chrome is a browser extension that adds HTML validation inside Developer Tools of Chrome. The number of errors of a HTML page is seen with an icon in the browser status bar.
Stack Overflow
stackoverflow.com › questions › 15227317 › browser-plugin-w3c-validator
google chrome - Browser plugin w3c validator? - Stack Overflow
Kingsquare HTML validator is probably your best bet. Install it, reload Chrome, and then inspect element and go to HTML validator. This works offline and doesn't need W3C servers.
GitHub
github.com › renyard › validity
GitHub - renyard/validity: A Google Chrome extension for validating HTML.
Validity can be used to quickly validate your HTML documents from the address bar. Just click the icon in the address bar to validate the current document without leaving the page.
Starred by 91 users
Forked by 26 users
Languages JavaScript 85.9% | HTML 11.1% | CSS 2.4% | Shell 0.6% | JavaScript 85.9% | HTML 11.1% | CSS 2.4% | Shell 0.6%
Rocket Validator
rocketvalidator.com › blog › chrome-extensions-for-html-validation
Chrome extensions for HTML validation · Rocket Validator
The Validity extension lets you validate HTML on the legacy W3C Validator, and shows the issues found on the JavaScript console, instead of opening a new tab.
Gueury
gueury.com › mozilla
Html Validator for Firefox and Chrome
HTML Validator is a browser extension that adds HTML validation inside Firefox and Chrome. The number of errors of a HTML page is seen on the form of an icon in the status bar when browsing. The details of the errors are seen when looking the HTML source of the page.
W3Schools
w3schools.com › w3css › w3css_validation.asp
W3.CSS Validation
The Validation Service was created by the W3C to help Web developers validate CSS. The W3C CSS Validator checks for CSS1, CSS2, CSS3, and CSS4 properties. Some browsers use vendor extensions to simulate CSS3 and CSS4 properties.
GitHub
github.com › cfjedimaster › brackets-w3cvalidation
GitHub - cfjedimaster/brackets-w3cvalidation: Simple W3C Validator for Brackets
A Brackets extension to enable W3C validation support. To use this extension, open any HTML file and then check the bottom right corner of Brackets (where all files are checked) and look for either the green icon (all is well) or the yellow ...
Starred by 85 users
Forked by 33 users
Languages JavaScript 100.0% | JavaScript 100.0%
Top answer 1 of 5
8
With this html validator extension. Or by Ctrl-U, copy-paste into the w3c page.
2 of 5
6
You have to run the service they provide on your server:
http://validator.w3.org/docs/install.html
Thats what we've done, works great.
I think it's best practice to be validating your sites source when it's in development not when its in production... Treat this just like running unit tests. You shouldn't have markup errors go live either.
GitHub
github.com › ggdavid › html-validity
GitHub - ggdavid/html-validity: Validate any webpage's HTML source or DOM using W3C tools. View detailed results directly in your browser console. · GitHub
HTML Validity is a simple Chrome extension that checks any webpage's HTML source or live DOM for validity using the official W3C validator.
Author ggdavid
Reddit
reddit.com › r/webdev › w3c validator alternatives for broken html?
r/webdev on Reddit: W3C Validator alternatives for broken HTML?
May 9, 2025 -
I've always used the W3C Validator to help find broken HTML elements, but I'm finding it's becoming quite outdated and throwing errors for things that are now valid.
Are there any better alternatives to finding broken HTML elements?
Top answer 1 of 11
5
Which of w3 validators do you use? What doctype is set on your documents? Give some examples of "valid things" that show errors in validator?
2 of 11
4
The main W3C validator has gone horrifically out of date. WHATWG recommends using the Nu HTML Checker from W3C instead: https://validator.w3.org/nu/ Nothing is more reliable than putting the HTML into a variety of web browsers and checking the console output, though.
npm
npmjs.com › package › w3c-html-validator
w3c-html-validator - npm
Check the markup validity of HTML files using the W3C validator. Latest version: 2.2.0, last published: 2 months ago. Start using w3c-html-validator in your project by running `npm i w3c-html-validator`. There are 4 other projects in the npm registry using w3c-html-validator.
» npm install w3c-html-validator
Published Jan 21, 2026
Version 2.2.0
Author Thomas Davis