For years the Unix tool HTML Tidy has been the de facto standard for cleaning, organizing, troubleshooting, and fixing HTML files from a wide variety of sources. Balthisar Tidy is the beautiful Macintosh OS X implementation of this this fine tool. With virtually all of the features of the command line tool and all of the text encodings that Mac OS X offers, as well as HTML5 support, Balthisar Tidy will be helping you post better code in no time.
This native Mac implementation of HTML Tidy is a great utility for doing all of this. It also works 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.