🌐
W3C
validator.w3.org
The W3C Markup Validation Service
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, or to find broken links, there are other validators and tools available. As an alternative you can also try our non-DTD-based validator.
W3 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 Feed Validation Service, for Atom and RSS
Check the syntax of Atom or RSS feeds · Validate a feed online:
w3 Validator
This Link Checker looks for issues in links, anchors and referenced objects in a Web page, CSS style sheet, or recursively on a whole Web site. For best results, it is recommended to first ensure that the documents checked use Valid (X)HTML Markup and CSS.
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
🌐
Auto Page Rank
autopagerank.com › home › technical seo › top 3 html 5 validator alternatives to boost your website’s seo
Top 3 HTML 5 Validator Alternatives to Boost Your Website’s SEO - Auto Page Rank - AI Content Marketing Software
September 12, 2025 - While the HTML5 Validator is a popular choice, it’s not the only option out there. Exploring alternatives can save you time and help you catch issues that might slip through the cracks, with tools like W3C Validator and Validator.
Top answer
1 of 2
6

Maintainer of the current W3C HTML Checker (validator) here. I think it's important to understand the intended purpose of the current HTML checker, which is different from the purpose of the legacy W3C Markup Validator.

The purpose of the checker is documented at https://validator.w3.org/nu/about.html#why-validate:

The core reason to run your HTML documents through a conformance checker is simple: To catch unintended mistakes—mistakes you might have otherwise missed—so that you can fix them.

Beyond that, some document-conformance requirements (validity rules) in the HTML spec are there to help you and the users of your documents avoid certain kinds of potential problems.

There are some markup cases defined as errors because they are potential problems for accessibility, usability, interoperability, security, or maintainability—or because they can result in poor performance, or that might cause your scripts to fail in ways that are hard to troubleshoot. Along with those, some markup cases are defined as errors because they can cause you to run into potential problems in HTML parsing and error-handling behavior—so that, say, you’d end up with some unintuitive, unexpected result in the DOM

Validating your documents alerts you to those potential problems.

So as far as your question about "are better approaches to ensure contemporary standards-compliant markup", the answer is that it's not an either-or thing; there are a variety of approaches and the W3C HTML Checker is just one of them, and its goal isn't to be the single way to determine anything but instead to just help you catch mistakes you might otherwise miss and that might cause unexpected problems for your users.


As far as ways to get alerted to specific device issues or browser-implementation issues, we don’t have good automated checking tools for that, but a couple of things which are huge help there are:

  • https://caniuse.com/ — detailed information about the level of support for particular web-runtime features in different browsers, and in different versions of those browsers, and in release of the browsers for mobile devices vs desktop

  • https://wptdashboard.appspot.com/ — current test results across all major browser engines for dozens of web-runtime features/specs; if https://caniuse.com/ doesn’t have information about a particular feature, you can look through this dashboard and browse to the directory that has tests for that feature, and find whether a browser passes the tests for the feature

But as far as good automated tools we do actually have for checking other things, here are two:

  • https://validator.w3.org/i18n-checker/ — W3C Internationalization Checker
  • https://observatory.mozilla.org/ — for doing a security assessment of the content of your site
2 of 2
-1

I recently faced a problem with mentioned above W3C HTML Checker. I respect a huge amount of work that was done by author of this validator, but it did not allow me in any way a tag <script type="text/vbscript" src="file.vbs">. It was said to change type value to empty string, a JavaScript MIME type, or module, which makes my page useless.

I know than VBScript language is rarely used now, it was just a test page, but let me share with you less tricky alternative, as good as the first one for HTML error checking.

Maintainer of the current JsonFormatter (validator) is here

🌐
Reddit
reddit.com › r/adops › html5 validator
r/adops on Reddit: HTML5 Validator
February 15, 2019 -

Google DCM HTML5 Validator will be deprecated without a replacement March '21..

Our studio relies on this to make sure creatives will not be rejected when uploaded to DCM. Anyone know of any alternatives? Thanks!

EDIT: Nevermind! deprecation postponed, thanks to anyone who raised concerns..

🌐
GitHub
github.com › InteractiveAdvertisingBureau › HTML5-AdValidator › issues › 19
HTML5 Ad validator alternative (CreativeQA.io) · Issue #19
June 30, 2021 - Since the ad validator is offline and this project seems to be discontinued, I take the opportunity to mention this free online alternative scanner: https://www.creativeqa.io/html5-ad-validator ·
Author   CreativeQA
🌐
AlternativeTo
alternativeto.net › software › html-validator
HTML Validator Alternatives and Similar Apps | AlternativeTo
The best HTML Validator alternatives are Scrutiny, Screpy and mailmouse. Our crowd-sourced lists contains six apps similar to HTML Validator for Web-based, Mac, Windows, Linux and more.
🌐
TemplateToaster Blog
blog.templatetoaster.com › templatetoaster blog › tips and tricks › 13 best free html validators in 2023
13 Best Free HTML Validators in 2023 - TemplateToaster Blog
June 8, 2023 - Validation tools make easier to scan code and detect error. CSS Validator. nu Validator Free. W3C HTML Validation. Firefox html Validator. Chrome HTML Validator. Rocket Validator. Aborla HTML Validator
🌐
Reddit
reddit.com › r/adops › html5 creative validation tools
r/adops on Reddit: HTML5 Creative Validation Tools
January 9, 2021 -

Hey all! Wondering what your thoughts are on ad validation. Reason being is because we are evaluating our current process and determining if we can do this faster.

We currently request our graphic design team (external agency) to send us all the files in a folder in a GWD format (includes json files). Then we have to import that into Google Web Designer, so that we can use the built in ad validator, and then publish and connect to Campaign Manager. This process can become quite tedious because we have to do these 1 by 1 and also connect backup creatives. So the process of open + validation + backup image + publishing creative & connecting to CM, all that can take maybe 1-2 minutes per creative. When you're talking about 30-60 creatives, that's a lot of time.

The alternative we are considering is to instead use the standard zip file format for HTML5 files, then batch validate with a tool like h5validator.appspot.com, then batch upload the files into CM. Assuming the files pass validation, that same process might take 5-10 minutes at most for hundreds of creatives.

So, questions here:

  1. Is the GWD built-in validator any different than a tool like h5validator? If so, how?

  2. How necessary would you say the html5 validation is?

  3. Do you have any other methods of efficiently validating and uploading HTML5 creatives into Campaign Manager?

Thanks for the input fellers!

Find elsewhere
🌐
AlternativeTo
alternativeto.net › software › batch-html-validator
Batch HTML Validator Alternatives and Similar Software | AlternativeTo
The best Batch HTML Validator alternatives are Scrutiny, Screpy and Rocket Validator. Our crowd-sourced lists contains five apps similar to Batch HTML Validator for Online / Web-based, Mac, Windows, Linux and more.
🌐
Software Testing Help
softwaretestinghelp.com › home › tools and services › 15 most popular html validator online tools in 2026
15 Most Popular HTML Validator Online Tools in 2026
December 5, 2025 - ... These tools are helpful for those clients and organizations that don’t have enough finance and just want to learn the coding or for those who just want to give it a try before starting any website on their own. ... The Nu HTML5 is a popular ...
🌐
Medium
medium.com › @gulshan_n › streamlining-your-code-top-online-html-validators-for-web-developers-49182f1e2d5c
Streamlining Your Code: Top Online HTML Validators for Web Developers | by Gulshan N | Medium
September 18, 2023 - Streamlining Your Code: Top Online HTML Validators for Web Developers Here is a list of some popular online HTML validators that you can use to validate your HTML code: 1- W3C Markup Validation
🌐
Reddit
reddit.com › r/ppc › html5 creative validation tools
r/PPC on Reddit: HTML5 Creative Validation Tools
January 9, 2021 -

Hey all! Wondering what your thoughts are on ad validation. Reason being is because we are evaluating our current process and determining if we can do this faster.

We currently request our graphic design team (external agency) to send us all the files in a folder in a GWD format (includes json files). Then we have to import that into Google Web Designer, so that we can use the built in ad validator, and then publish and connect to Campaign Manager. This process can become quite tedious because we have to do these 1 by 1 and also connect backup creatives. So the process of open + validation + backup image + publishing creative & connecting to CM, all that can take maybe 1-2 minutes per creative. When you're talking about 30-60 creatives, that's a lot of time.

The alternative we are considering is to instead use the standard zip file format for HTML5 files, then batch validate with a tool like h5validator.appspot.com, then batch upload the files into CM. Assuming the files pass validation, that same process might take 5-10 minutes at most for hundreds of creatives.

So, questions here:

  1. Is the GWD built-in validator any different than a tool like h5validator? If so, how?

  2. How necessary would you say the html5 validation is?

  3. Do you have any other methods of efficiently validating and uploading HTML5 creatives into Campaign Manager?

Thanks for the input fellers!

🌐
PPC Land
ppc.land › html5-validator-tool-for-campaign-manager-to-be-deprecated-in-april-2025-2
HTML5 validator tool for Campaign Manager to be deprecated in April 2025
January 27, 2025 - Another alternative, PreviewAds.com, launched in beta with plans to replicate and expand upon Google's validation capabilities. The original html5 validator tool has specific technical requirements for creative assets. It accepts zip files containing all necessary assets, with the condition that uploaded content must have appropriate legal rights and avoid sensitive material.
🌐
GitHub
github.com › validator › validator
GitHub - validator/validator: The Nu Html Checker (vnu) · GitHub
The Nu Html Checker (vnu) — along with being usable as a standalone command-line client — can be run as an HTTP service, similar to validator.w3.org/nu, for browser-based checking of HTML documents, CSS stylesheets, and SVG images over the Web.
Starred by 1.9K users
Forked by 321 users
Languages   Java 91.3% | ANTLR 6.6% | Python 1.4% | TypeScript 0.4% | Makefile 0.3% | Shell 0.0%
🌐
Validator
about.validator.nu
About Validator.nu
If you want to create you own alternative mode of input or want to call Validator.nu (or your own local copy) from within your own application, there is a RESTful Web service API. In addition to the modes of input that work from HTML forms, you can also POST the document to be checked as an ...
🌐
Appspot
h5validator.appspot.com › dcm
HTML5 Validator
Privacy Policy - Terms of Service · Feedback · feedback