How plagiarism checkers work

An online plagiarism checker compares the text you give it against other text and reports where the two overlap. The details differ between tools, but the method falls into a few steps.

1. The text is split into passages

A checker does not compare a whole paper in one go. It breaks the text into sentences or phrases and chooses the ones most likely to be unique to the author: longer passages made of less common words. Short generic sentences are skipped because they match thousands of unrelated pages.

2. Each passage is searched for

plagiarism.ink searches the web for each chosen passage as an exact phrase. If the identical string of words appears on another page, that page is reported as a match. Tools that compare against a private database of earlier submissions work the same way, with a different pool of text to search.

3. You review the matches

The checker can only tell you that the same words exist elsewhere. It cannot tell you who wrote them first, whether the source was cited, or whether the overlap is innocent. Typical harmless matches include:

direct quotations that are properly cited;
names, titles, definitions and standard phrases;
bibliography entries;
text the same author published elsewhere.

Matches that deserve a closer look are long runs of identical wording with no quotation marks or citation.

What a plagiarism checker cannot do

It cannot find copying from sources that are not online or not indexed, such as printed books or another student's private essay.
It will miss heavy paraphrasing that keeps the ideas but changes the wording.
It cannot prove intent. A person has to make that call.

Try it

Paste your text into the free plagiarism checker. Teachers can read how to use it with student work, and students can read how to check a draft.