...you might consider the standalone version of Tidy for html...

I agree. It's very nifty indeed, easy to use and highly configurable.

Something as simple as:

my $in  = 'bad.html';
my $out = 'tidied.html';
my $err = 'tidy.err';
my $cnf = 'tidy.cnf';

system( 
  'tidy.exe',
  '-asxml',
  -config => $cnf,
  -file   => $err,
  -output => $out,
  $in,
);
[download]

can be easily adapted to process a list or even a local copy of a web site. The config file can be tweaked to be severe or lenient to taste.

You can easily interrogate all the error files to get a good picture of how bad the html is (and there is a lot of it about!).

Again, I agree. Why bother to go to a lot of trouble when there is a very clever bit of kit available.