Total Validator is an HTML validator, an accessibility validator, a CSS validator, a spell checker, and a broken links checker all rolled into one tool allowing one-click...
Advanced graphical XML editor, code generator and toolkit for complying with W3C standards.
Regular Expression Tester with highlighting for Javascript and PCRE. Quickly test and debug your regex.
FormValidation - The best jQuery plugin to validate form fields, support Bootstrap, Foundation, Pure, Semantic, UIKit frameworks