Punctuation of Isn't it

Solution 1:

Use a question mark at the end, not a period. The short clause at the end of the statement changes it into a question.

In "It's a beautiful day, isn't it?", "isn't it?" is the question tag.

You use a question tag to see if the listener agrees with what you have said.

For example, in "He went to the office, didn't he?", "didn't he?" is the question tag.

In "He didn't go to the office, did he?", "did he?" is the question tag. You think he didn't go to the office, but you want to confirm it.

Two more examples:

"He has eaten his breakfast, hasn't he?"

"He hasn't eaten his breakfast, has he?"