Going as far back as the debut version, HTML-Kit had provided a built-in option for catching errors in HTML documents. This was made possible with the help of the excellent HTML Tidy utility written by Dave Raggett. In fact, HTML-Kit was the first program to provide a graphical user interface for HTML Tidy.
HTML Tidy is keeping up with the times by improving support for HTML5 and so is HTML-Kit Tools.
To check your HTML 5 documents, as well as older versions of HTML and XHTML documents, open them in HTML-Kit Tools and press F9 key. Alternatively, you can click the Tidy tab at the bottom of editor windows for a comparison (diff) of the original HTML code and the code suggested by HTML Tidy. Configuration and other options such as beautifying HTML are located on the main menu under "Tools > Tidy".
Improved HTML5 support checks for new elements in the latest HTML specification, including article, audio, canvas, footer, header, nav, rp, rt, ruby, section and video. New attributes that are checked include custom data-* attributes, contenteditable, contextmenu, draggable, dropzone, hidden, spellcheck, and the many form and event attributes introduced in HTML version 5.