We can add question tags like isn't it?, can you? or didn't they? to a statement to make it into a question. Question tags are more common in speaking than writing.
We often use question tags when we expect the listener to agree with our statement. In this case, when the statement is positive, we use a negative question tag.
Examples:
She's a doctor, isn't she?
Yesterday was so much fun, wasn't it?
If the statement is negative, we use a positive question tag.
He isn't here, is he?
The trains are never on time, are they?
Nobody has called for me, have they?
If we are sure or almost sure that the listener will confirm that our statement is correct, we say the question tag with a falling intonation. If we are a bit less sure, we say the question tag with a rising intonation.