就是了【jiùshì le】

就是了 at the end of a sentence says the thing just named is all that's needed – no fuss, no more discussion. It's spoken. After a promise it reassures; after an instruction it tells the listener to stop worrying and do it.

Promises

With 我 as the subject, 就是了 settles someone's worry or ends an argument. 放心 or 好 often comes first, and it can sound a little impatient.

Instructions

With 你 or no subject, it tells the listener what to do and implies nothing else matters.

Not "that's all" about a fact

就是了 is about what to do now or next. To shrink a fact – "I only bought one, that's all" – use 罢了 or 而已.

• × 我昨天只买了一本书就是了 → 我昨天只买了一本书罢了

就是 inside a sentence is a different word, for emphasis or for "it's just that": 好看，就是贵.