The Scribbr Plagiarism Checker compares your document against the largest plagiarism database in the world. It will detect any similarities with documents in that database.
However, you might be unsure if all of the sources you used are in that database – for example, because some of your sources are unpublished. In this case, you can make use of our Self-Plagiarism Checker. Here you can add all the sources you want to a private database and compare them with your own document.