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Common Passages Finder

Finds identical passages shared by two texts from N words up, lists each one with its position and reports the overlap percentage.

Between 3 and 30. Six words is a good starting point for prose; raise it if the list fills up with stock phrases.

When comparing, ignore

Both texts stay in your browser. The comparison runs locally and nothing is uploaded.

How the matching works

Both texts are split into words. Every window of N consecutive words from text A goes into an index; text B is then scanned with a window of the same size, and each hit is extended forward while the following words keep matching. That is why the passages you see are maximal: a fifteen-word overlap shows up once, not as ten overlapping six-word fragments.

The percentage counts words covered by at least one shared passage, divided by the total number of words in that text. The two sides usually differ: a short text reused inside a long one shows high coverage on the short side and low coverage on the long one, which is exactly the asymmetry a single similarity score hides.

See which sentences two texts share

A single similarity score leaves the real question open: 38 percent alike might mean two long copied sentences or just similar vocabulary spread evenly. This page answers with a list instead. Every repeated passage shows up whole, with its word count, its line and its position in each text, and the side panels mark those passages inside the original wording.

The search works on windows of N consecutive words. With the minimum at 6, each run of six words in text A becomes a key; when the same key turns up in text B, the match is stretched forward while the following words keep agreeing. An eighteen-word overlap therefore appears as one passage rather than thirteen overlapping six-word fragments.

The two percentages are almost never equal, and the gap between them carries most of the meaning. A 200-word press release reused inside a 1,500-word article covers close to 100 percent of the release and close to 13 percent of the article. Reading only one of those figures leads to opposite conclusions about the very same pair.

Frequently asked questions

What minimum length should I pick?
Six words works well for ordinary prose. Below four the list fills with phrases anybody would write, such as on the other hand or according to the. For technical texts packed with fixed terminology, raising it to eight or ten keeps only the passages that were genuinely reused.
What does ignoring function words do?
With that option on, articles, prepositions and pronouns are dropped before matching. Two sentences reworded only in their connectives, such as climbed on the roof of the house and climbed onto a roof of a house, then count as the same passage. The result is still displayed with the original spelling.
Are the texts uploaded anywhere?
No. The whole comparison runs in your browser in JavaScript, and the page makes no network request with what you pasted. Open the browser network tab before clicking compare and you will see it: nothing leaves the machine, not even for texts hundreds of thousands of characters long.

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