Question tags with auxiliary verb
If there is an auxiliary verb (be, have, do, is, etc.) in the main sentence, the question tag also contains the same auxiliary verb.
E.g. It’s raining, isn’t it?
Similarly, if there is a modal verb (could, can, should, etc.) in the main sentence, the question tag is also constructed with the same modal verb.
E.g. They couldn’t hear him, could they?
Question tags without auxiliary verb
In case, the main part of the sentence doesn’t contain an auxiliary verb, the question tag is constructed with the relevant form of ‘do’. E.g. He eats fish, doesn’t he?
Exceptions in question tags:
There are certain peculiarities in the usage of question tags that doesn’t follow the above mentioned rules.
Examples:
I am right, aren’t I?
Let’s go to the beach, shall we?
Wait a minute, can you?
Have some more rice, will you?
Somebody has called, haven’t they?
There is a mosque in that street, isn’t there?