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, …

Validate by Direct Input ... If your document is on the Web, you can validate it by entering its address instead. Home About... News Docs Help & FAQ Feedback Contribute

If your document is on the Web, you can validate it with the same advanced options by entering its address instead.

The Markup Validator is a free tool and service that validates markup: in other words, it checks the syntax of Web documents, written in formats such as (X)HTML.

Validation is one of the simplest ways to check whether a page is built in accordance with Web standards, and provides one of the most reliable guarantee that future Web platforms will …

This page lists recent changes to the W3C Markup Validation Service. For minor changes and bug fixes that aren't listed on this page, see the GitHub repo. Want to know not just the latest …

For programmatic checking of modern HTML documents, use the API provided by the W3C HTML Checker. To do that, call https://validator.w3.org/nu/ or the URL for another instance of the …

The Markup Validator is a free service by W3C that helps check the validity of Web documents. Most Web documents are written using markup languages, such as HTML or XHTML.

When you call http://127.0.0.2/ in your browser, you should see the well-known site from https://validator.w3.org/. In the configuration file of the Apache, a name for the Virtual Host …

This list conveniently gathers all the error messages currently used by the validator when processing Web documents, and the community-contributed explanations to these error …