Now I found this great utility. If
1. you are having some errors in your html pages.
2. you want to improve your html pages.
3. you want to optimize your html pages.
Any one of the above or all of the above is your need then this utility is probably all you are going to need.
It was made by Dave Raggett and now maintains by volunteers. It is open source.
You can use it online at w3c :HTML Tidy Project Page
If you want to download it then you can use :HTML tidy service

It must be noted it will corrects errors only if its know about them. Otherwise, it will just flags as errors and warnings. A must have utility for web designer.
There's a css tidy also but it is dead for a while.