What Tidy Can and Cannot Do
While I consider Tidy to be an indispensable tool for anyone who works with web documents, it has strengths and weaknesses just like any other piece of software. Tidy's strengths are obvious:
Tidy quickly and efficiently fixes most problems with HTML files.
Versions of Tidy are available for many operating systems, including Windows, DOS, Mac OS, several flavors of UNIX/Linux, and BeOS.
The weaknesses are actually not that bad:
Unfortunately, Tidy can't always fix every problem it finds. You'll often run into problems with tables, for example. For a table to be considered accessible, it needs a summary attribute in the <table> tag. Tidy has no function to add the summary attribute automatically. You must correct this type of error by hand.
Because it's a command-line tool, Tidy doesn't appeal to anyone who is accustomed to the point-and-click convenience of a graphical user interface.
Sometimes you have to run Tidy two or more times to completely clean a file.