Html5 Validator

https://html5.validator.nu
Nu Html Checker This tool is an ongoing experiment in better HTML checking and its behavior remains subject to change

https://www.freeformatter.com/html-validator.html
Validates HTML files for compliance against the W3C standards and performs linting to assess code quality against best practices Find missing or unbalanced HTML tags in your documents stray characters duplicate IDs missing or invalid attributes and other recommendations Supports HTML5 SVG 1 1 MathML 3 0 ITS 2 0 RDFa Lite 1 1

https://appdevtools.com/html-validator
HTML Validator is a free online developer tool to validate HTML code against the W3C standards as known as HTML linter instantly Supports partial HTML code validation You can either browse an HTML file fetch HTML code from a URL or paste HTML code manually and then click the validate button

https://en.rakko.tools/tools/58
Developers to review HTML source code quickly Checking if the images in the HTML content are displayed the alt attributes are not missing or the alt content or the image name match the image content so that you can fix them for optimizing the search engines

https://www.lambdatest.com/free-online-tools/html-validator
The HTML Validator checks the code for correct syntax proper use of tags and attributes and compliance with the HTML specification It identifies and reports any errors or warnings that it finds such as missing tags incorrect attribute values and non compliant code

https://validator.w3.org/about.html
This validator can process documents written in most markup languages Supported document types include the HTML through HTML 4 01 and XHTML 1 0 and 1 1 family MathML SMIL and SVG 1 0 and 1 1 including the mobile profiles

https://dev.w3.org/validator/htdocs/docs/users.html
The W3C Markup Validation Service is a web gateway to a well known SGML parser called SP SP will take your HTML and compare it to a set of objective syntax rules called a DTD a Document Type Definition This way you can be sure your HTML is really valid and not just that it conforms to some random programmer s idea of nice HTML

https://www.w3.org/QA/Tools
Good tools cost a lot to develop support host and maintain With your help we can make the tools and validators better faster friendlier and maintain a great free service for all of the Web This page lists the validators and web developer tools

https://developer.mozilla.org/.../Form_validation
This is called client side form validation and helps ensure data submitted matches the requirements set forth in the various form controls This article leads you through basic concepts and examples of client side form validation