Isn’t it? is a form of question tag.
We use tags in spoken English but not in formal written English.
They are not really questions but are a way of asking the other person to make a comment and so keep the conversation open.
Making a tag is very mechanical. To make a tag, use the first auxiliary. If there is no auxiliary, use do, does or did. With a positive sentence, make a negative tag and with a negative sentence, make a positive tag.
- It’s beautiful, isn’t it?
- He has been, hasn’t he?
- You can, can’t you?
- It must be, mustn’t it?
- You know him, don’t you?
- He finished it, didn’t he?
- He will come, won’t he?
- It isn’t very good, is it?
- It hasn’t rained, has it?
- It can’t be, can it?
- Jenny doesn’t know James, does she?
- They didn’t leave, did they?
- He won’t do it, will he?
- There isn’t an ATM here, is there?
- Let’s have a cup of coffee, shall we?
To reply, use the same auxiliary:
- It’s beautiful, isn’t it? ~ Yes, it is. I think it’s fabulous.
- It isn’t very good, is it? ~ No, it isn’t. In fact, it’s terrible.
Although, the rules are very simple and mechanical, in order to use them easily in conversation, they have to be automatic. So you need to hear and practice them very often.