Text Similarity Checker
Compare two documents and see exactly which passages overlap.
Shorter settings catch more paraphrasing but also more coincidence — any two essays on the same topic share four-word runs. Five is a sensible default.
Paste both texts
This compares the two documents you provide. It cannot search the web — see the note below.
This is not a web plagiarism scan. It compares the two texts you paste in, and only those. Checking a draft against everything ever published needs a crawled index of the whole web, which no free browser tool has — so rather than pretend, this does the job it genuinely can: showing you exactly which passages you have reused from a source you already have, so you can quote and cite them properly.
Private by design. This tool runs entirely in your browser. Your input is processed on your own device and is not uploaded by DO101.
About the Text Similarity Checker
Paste your draft and a source, and see every run of matching words highlighted in both, with an overlap percentage. Built for checking that what you took from a source is properly quoted and cited. It compares the two texts you give it — it does not search the web, and it says so instead of pretending otherwise.
How to use it
- 1Paste your draft on the left and the source on the right.
- 2Matching passages are highlighted in both texts as you type.
- 3Click any passage to line it up against its match in the other document.
- 4Adjust the match length if you want to catch shorter or only longer runs.
What you get
- Overlap percentage using n-gram containment, the standard reuse measure
- Every matching passage highlighted in both documents
- Adjustable match length from 3 to 10 words
- Longest matching run, which is usually the most telling number
- Common stopword phrases excluded so coincidence does not inflate the score
- Nothing uploaded — both documents stay in your browser
Frequently asked questions
Is this a plagiarism checker?
Not in the sense most people mean. It compares the two texts you paste in and nothing else. Checking a draft against everything ever published needs a crawled index of the web, which costs real money to build and run, so no free browser tool has one. What this does instead is the part that is genuinely doable: showing you which passages you reused from a source you already have.
What counts as too much overlap?
There is no universal threshold, and your institution may set one. As a rule of thumb, anything above about 15% that is not inside quotation marks with a citation is worth rewriting or attributing properly.
Why does it find matches in two unrelated essays?
Any two texts on the same topic share short runs of common phrasing. That is why the default match length is five words and stopword-only runs are ignored. Raise the match length if you only want longer, more meaningful overlaps.
Can I check my own earlier work against a new draft?
Yes, and that is one of the better uses for it. Self-plagiarism rules catch people out, and comparing a new draft against a previous submission is exactly what this does well.
Keep going
People who use this tool usually reach for these next.
APA, MLA, Harvard, Chicago, IEEE and Vancouver references.
Catch spelling, grammar, punctuation and wordiness as you type.
Compare two texts and highlight every change.
Tighten wordy writing with every edit shown and reversible.