HTML Tidy is a console application for correcting invalid HyperText Markup Language (HTML), detecting potential web accessibility errors, and for improving the layout and indent style of the resulting markup.

It is also a cross-platform library for computer applications that provides HTML Tidy's features.

HTML Tidy was developed by Dave Raggett[2] of the World Wide Web Consortium (W3C).

[3] In 2012, the project was moved to GitHub,[4] and maintained by Michael Smith, also of W3C,[5] where HTML5 support was added.

Up-to-date versions are available as source code cloned from its GitHub Git version control repository, or in binary packages for multiple operating systems from its GitHub Releases repository.