PPTools/Tidy
Tidy: HTML Source Check
What
From the W3C site:
When editing HTML it's easy to make mistakes. Wouldn't it be nice if there was a simple way to fix these mistakes automatically and tidy up sloppy editing into nicely layed out markup? Well now there is! Dave Raggett's HTML TIDY is a free utility for doing just that. It also works great on the atrociously hard to read markup generated by specialized HTML editors and conversion tools, and can help you identify where you need to pay further attention on making your pages more accessible to people with disabilities.
Where
Since 2015 Tidy can be downloaded from GitHub. Ready to run programs and sourc code:
Includes Ready to run programs and source code for Linux, MacOS and Windows.
HTML Tidy website: https://www.html-tidy.org
Project page on GitHub: https://github.com/htacg/tidy-html5
Old version (2008):
Tidy can be downloaded from SourceForge. Ready to run programs: :http://tidy.sourceforge.net/#binaries Source code: :http://tidy.sourceforge.net/#source
Install
Unix-like Systems
The Linux/Unix packages are gzipped tar archives (mostly). The standard operation: tar -xzf file.tgz unpacks a bin/ directory with tidy within. Move it wherever most convenient; /usr/local/bin is a good place.
The program may be available in your distribution's repos for installation with a package manager, e.g. the package "tidyhtml" in archlinux.
Windows
Simplest is to download this file:
Unzip and place in a convenient location. Same directory with all your other PP tools such as guiguts would be a nice choice.
Slightly more complex is the self-installer:
Click on the .exe file and follow the prompts adjusting to your taste.
This package has some additional documentation not included with the zip version.