Along with the already mentioned W3C HTML validator, you can also upload local files.
http://validator.w3.org/#validate_by_upload
There is also a Microsoft visual studio for checking web forms:
When you edit the markup in the Visual Studio web designer (for web form pages, in the "Source" view), the editor checks the markup for correctness. Markup validation works like spellchecking in a word processing program. The editor checks the markup and adds wavy red lines below elements or attributes that are invalid.
http://msdn.microsoft.com/en-us/library/f940516c.aspx
There are also text editors such as Dreamweaver that will check your code for errors.
In fact, Notepad ++ is also good for checking out various language formats.
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