What does the algorithm for checking text for uniqueness on the network look like?

Question

PHP

There are a number of services on the network that allow you to check the uniqueness of the text. What does the verification algorithm look like? Please share your experience or description of how this can be implemented.

Answer 1

Set yourself advego desktop plagiarism and intercept traffic from it.
It breaks the text into semantic pieces and looks for them in different search engines up to the Nth page of the issue