I used the W3 Template Validator, and got hundreds of errors! Is my blog broken?This blog owner, like many others, does not understand the differences between W3 Standard HTML / XHTML, and Blogger HTML / XML.
The unpleasant truth is that, ever since Blogger released the Layout class templates, in 2007, Blogger has been providing templates that can't be successfully validated using HTML / XHTML standards. Blogger has a lot of features that don't validate, according to public standards.
That's not to say that the W3 Template Validator, and similar online analysis tools and code validators won't be useful, in helping you proactively check your blog for problems.
If you've tweaked your template, and / or added various HTML based accessories, you may find a few informative entries, in a typical validation report.
Upon examining the validation report for this blog, I can find more than a few references to various accessories and tweaks that I've made in the past, which I can identify. Some of the 498 errors (as of today) can maybe be fixed - but many can't.
If you want to look for problems with your blog, start by creating a test blog, using the same template that you have. Then, run the validation of your choice against your test blog. The report that comes from your test blog, you can use as a baseline.
Take your baseline report, and compare it with the report for your working blog. Unless you've done a lot of customisation to your blog, you'll find a lot more errors identified on both reports, than not. You can (maybe, should) fix the problems which are unique to your working blog - and you may have to walk away from the others.
Like the frustrations caused by referer spam, which you learn to live with, I may have to ignore some coding imperfections. Your blog may be the same.