What this tool actually checks, and what it doesn't
A genuine, comprehensive plagiarism check requires comparing a piece of text against the entire indexed web, which means crawling and searching billions of other pages — something that fundamentally requires a large, continuously updated server-side index and cannot be done by a page running only in your browser. Rather than pretend to offer that with a purely cosmetic scan, this tool does something narrower but fully honest: it directly compares two specific texts that you paste in, and reports how much they overlap in exact phrasing.
This is most useful for a specific, common situation: checking your own content against itself across different pages of the same site, or against a draft you're revising, to catch accidental duplication — a product description copy-pasted across dozens of near-identical product pages, a boilerplate paragraph reused so often it starts to look templated, or a new draft that unintentionally echoes an older page too closely. It is not a substitute for a dedicated, web-scale plagiarism detection service if you need to verify originality against the wider internet.
How the comparison works
The tool breaks each text into overlapping five-word sequences (a common technique called shingling) and measures what fraction of those sequences appear identically in both texts, expressed as a percentage. Five-word phrases are long enough that a match is unlikely to happen by coincidence in ordinary writing, but short enough to catch meaningful chunks of reused text even when they sit inside otherwise different sentences. The table beneath the result lists the actual shared five-word phrases found, so you can see exactly which sections overlap rather than just trusting a single summary percentage.
A low overlap score doesn't mean the two texts cover different ideas — it specifically means they don't share much identical wording, which is a different and narrower thing than topical similarity. Two well-written, completely original pages covering the same subject in different words will correctly score very low here even though they're about exactly the same topic, since this tool measures exact phrase reuse, not conceptual overlap.
Reading the result sensibly
Some overlap between two related pages on the same site is normal and not a problem — shared product specifications, a consistent brand tagline, or standard legal disclaimer text will naturally produce some phrase matches without indicating a genuine duplicate content issue. A high score across long stretches of body copy, on the other hand, particularly across two pages meant to serve different search queries, is worth a closer look, since search engines can treat near-duplicate pages as competing with each other rather than reinforcing a site's topical authority, sometimes resulting in only one of the pages being indexed prominently.
If you find a genuinely high overlap between two pages that are supposed to serve different purposes, the fix is usually to rewrite the more redundant of the two around what makes it distinct — a different angle, a more specific audience, or a narrower sub-topic — rather than simply deleting one page outright, since both may still serve a legitimate purpose once they're clearly differentiated in wording as well as intent.