Is it a correct sentence "the parameter is exist"?
I think we cannot write something like 'it is exist' or 'it is exists' because we should put some description or the state of an object after "is", but "exist" is a verb (action). Am I right? My colleague says that he encountered phrases like that. I would say "it exists" or "it is present" instead.
If you need context we want to describe pieces of data in computer memory, each of them might be stored or not depending on a device model.

Question

Is it a correct sentence "the parameter is exist"?
I think we cannot write something like 'it is exist' or 'it is exists' because we should put some description or the state of an object after "is", but "exist" is a verb (action). Am I right? My colleague says that he encountered phrases like that. I would say "it exists" or "it is present"  instead. 
If you need context we want to describe pieces of data in computer memory, each of them might be stored or not depending on a device model.

Answer

You are correct.  The phrases "it exists" or "it is present" are both correct.

Answer

The parameter is already existing at the point we are considering.
the parameter is existing in this namespace - 
the parameter exists in this namespace -