Are plagiarism checkers accurate?
The accuracy depends on the plagiarism checker you use. Scribbr is the most accurate plagiarism checker. Many free plagiarism checkers fail to detect all plagiarism or falsely flag text as plagiarism.
Take a look at this comparison of free and paid plagiarism checkers for students to find the most accurate plagiarism checker.
The accuracy is determined by two factors: the algorithm (which recognizes the plagiarism) and the size of the database (with which your document is compared).
Size of the database
Many free plagiarism checkers only check your paper against websites – not against books, journals or papers previously submitted by other students. Therefore, these plagiarism checkers are not very accurate, as they miss a lot of plagiarism.
Most plagiarism checkers are only able to detect “direct plagiarism”, or instances where the sentences are exactly the same as in the original source. However, a good plagiarism checker is also able to detect “patchwork plagiarism” (sentences where some words are changed or synonyms are used).