You mean, like html tidy (on Sourceforge and the original page, also on CPAN)? It doesn't work for HTML templates, but it works for the output generated by your templates. Well, actually, it works for a certain kind of HTML Templates, namely those used by Petal. If you're using a different templating system, you will need to check the output. But you want to do that anyway, as invalid input to your templates can generate invalid output.