Is this dofollow?

If I submit my link and a dofollow high PR page. But that page is restricted in robots.txt, so that link is useless?

 

Yes, search engines won't even index that page.

 

worthless imo

 

so how can we know it is useful? can you tell me some tool?

 

I think the answer is No. Its useless and would be time wasting aspect.
Move on to other Link IMO.

 

Google webmaster tools will tell you about your own restricted urls. I have one now. So google is warning me that unless I want it that way, they are going to eventually leave it alone.

 

So why are you going to restrict such a page if that is important to you anyway? If you need that blocked, so will be the links on that.

 

Unfortunatelly you are right..
It is completely useless.