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 , …

HTML tidy, originally developed at W3C, is a program that can help automatically clean up HTML pages. The WDG HTML validator is another excellent online validation service. A Real …

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. The Validator is sort of like lint …

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

For elements intended to be rendered as HTML, like RSS description, make sure that all plain text content is escaped first as HTML and then again as XML. For Atom text constructs, you can …

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 …

Check the markup (HTML, XHTML, …) of Web documents Test Suite Index This page lists a few test documents and test scenarios for the W3C Markup Validator make sure everything works …

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 document does not look like HTML, therefore automatic fallback could not be performed, and the document was only checked against basic markup syntax. Learn how to add a doctype to …

If the purpose of the markup is to escape the use of an HTML entity, use this table to find the Entity Number to replace the escaped version of the Entity Name. For example: © …