Find the passages in your text that already exist somewhere on the web.
A plagiarism checker compares your text against an index of pages it can reach. It finds published web content well and misses anything behind a login, inside a paid journal, in a printed book, or in another student's unpublished essay. A clean result is evidence of no web match, not proof of originality.
Quoted material, standard legal phrasing and common definitions all produce matches. Read what matched before drawing a conclusion — a 12% score made of cited quotes is fine, and a 3% score can be the one sentence that was lifted.
Up to 150,000 characters per check. Deep web-index checks are rate-limited daily rather than paywalled, because each one costs money to run.
It means nothing matching was found in the web index. Books, paywalled journals and unpublished work are outside any checker's reach.
No. Your text is used for the comparison and then discarded.