High Quality Content by WIKIPEDIA articles! HTML Tidy is a computer program and a library the purpose of which is to fix invalid HTML and to improve the layout and indent style of the resulting markup. It was developed by Dave Raggett of W3C, then passed on to become a Sourceforge project. Its source code is written in ANSI C for maximum portability and precompiled binaries are available for a variety of platforms. It is available under the W3C license (a permissive, BSD-style license).