AI detection tools are primarily designed to find content that was made by AI. They mark any parts that look like they were not originally written by a human.
Their main job is to distinguish between text written by a person and text written by a computer.
On the other hand, plagiarism checkers look for material that has been copied or is not original. They compare the text against a huge database of other works to see if there are any parallels or signs of plagiarism.