不是吗 is a tag question added to the end of a statement to invite agreement, similar to English 'isn't it?' or 'right?'. The 是 (shì) does NOT have to match the verb of the main clause — 不是吗 works for any sentence: 你来了，不是吗？(You came, didn't you?).
mistakes
Don't confuse with 是不是 (shì bú shì), which is a yes-or-no question word at the start or middle of a sentence. 不是吗 is always sentence-final and seeks confirmation, not information.
