What is a plagiarism checker?
When people say plagiarism checker, they often mean a service that scans billions of web pages. This tool does something narrower and more transparent. You give it two pieces of text, and it tells you how much they overlap.
Here is how it works. The tool lowercases both texts, strips punctuation, and breaks each into overlapping phrases of 3, 4, 5 or 6 words (you choose). It can also skip common words such as "the" and "and" before building phrases. The similarity score is the share of phrases in Text B that also appear in Text A. Matching phrases are highlighted in both boxes, and four counters show phrases in A, phrases in B, matched phrases and unique phrases in B.
The comparison is one way. It tells you how much of B is found in A, not the reverse. Because it only knows the two texts you paste, it cannot tell you whether either one was copied from a website, a book or an AI tool. Use it to compare a draft against a source you already have, or two versions of your own page.
How to compare two texts with this tool
- Paste the source or original wording into Text A (Original / Reference).
- Paste the text you want to examine into Text B (Check for Plagiarism). Word counters under each box update as you type.
- Set N-gram size (phrase length): 3 words is strict, 4 balanced, 5 lenient and 6 very lenient.
- Leave Ignore common words on Yes, or switch it to No to count every word.
- Click Check for Plagiarism. The score card, gauge and four counters appear.
- Read the highlighted matches in both boxes and rewrite the passages in Text B that match.
What this tool includes
Similarity percentage
The score is matched phrases divided by all phrases in Text B. The card is green below 20%, amber from 20% and red from 50%.
Adjustable phrase length
Choose phrases of 3 to 6 words. Shorter phrases flag more overlap, longer ones only flag close copying.
Stop word option
With common words ignored, phrases are built from the remaining words, which reduces false matches on filler.
Highlighted matches
Matches are marked in yellow in Text A and in green in Text B, so you can see exactly what repeats.
Four counters
See phrases in A, phrases in B, matched phrases and unique phrases in B at a glance.
Word counts
Each box shows a live word count.
Who uses it, and for what
- Content writers. Compare a rewritten paragraph with the source brief to make sure it is not too close to the original.
- Site owners with similar pages. Paste two product descriptions or location pages and see how much wording they share before Google treats them as near-duplicates.
- Editors. Compare a freelancer's draft with a competitor's article you suspect it borrowed from, then ask the writer to revise.
- Students checking their paraphrasing. Compare your summary with the passage you summarised. Pair it with the Word Counter to keep length in check.
Tips for accurate results
- Put the original in Text A and the suspect text in Text B. The score measures how much of B appears in A.
- Start with 4 words. Use 3 for a strict check of rewritten text, and 5 or 6 if common phrases are causing noise.
- Keep Ignore common words on. Turning it off can raise scores for text that simply shares ordinary wording.
- Quoted material and shared names will count as matches. Judge highlighted passages yourself.
- Short texts give unstable results. A 50-word paragraph can swing a lot from one shared sentence.
- A low score here does not prove originality. For web-wide checks, use a dedicated service, and see the Readability Score Checker to improve the rewrite.
Is it safe? Privacy and limits
Both texts are compared in your browser using JavaScript. Nothing is uploaded or stored by this tool, so it is suitable for unpublished drafts. Because it never contacts a search index or any database, it cannot detect copying from sources you did not paste. The score is a rough measure, not proof of plagiarism, and should not be the only basis for any academic or legal decision.
Plagiarism checker FAQ
It compares two texts that you paste and reports how much of the second text repeats phrases found in the first. It splits both into overlapping word sequences, finds the ones they share and shows the percentage, the counts and highlighted matches. It is a local comparison, not a web search. So it answers the question 'how similar are these two texts?' and not 'was this copied from somewhere online?'.
No. It only knows the two texts in the boxes. It does not contact a search engine, a publisher database or an AI detector. If you need to check a document against the web, use a service built for that, such as Copyscape or your institution's software. This tool is more like a diff for meaning-level overlap: useful when you already have the likely source and want to measure how close you are.
Both texts are lowercased, punctuation is removed, and words of one letter are dropped. If you keep Ignore common words on, a list of common English words is also removed. Then the tool builds the set of phrases with your chosen length. The score is the number of phrases in Text B that also exist in Text A, divided by the number of unique phrases in Text B, times 100. It is one-directional, and repeated phrases are counted once.
Four words is a good starting point. Three-word phrases are strict and will catch light rewording, but also common expressions. Five and six words are lenient and mostly flag near word-for-word copying. If your result seems too high because of stock phrases, move up one size. If a paraphrase seems to pass too easily, go down. The same two texts can score very differently at 3 and 6, which is expected.
There is no official threshold. This tool colours scores under 20% as low, 20% to under 50% as moderate and 50% or more as high. Those bands are rules of thumb. A high score on a short quotation-heavy text may be fine, while a low score can still hide paraphrased copying of ideas. Read the highlighted sections and decide yourself. Organisations such as schools and publishers set their own limits.
No. It has no model of how AI writes, and it only compares the two texts you give it. Similar wording between two AI outputs may show up as overlap, but a low score says nothing about who or what wrote a text. Do not use this tool as evidence of AI use. Treat it as an overlap measurement between a pair of documents.
It can. If large parts of one page repeat another page, search engines may show only one of them, and Google may choose a different version than you want. This is usually a filtering issue, not a penalty, unless the copying is deceptive. For your own pages, compare them here, then fix overlap with unique wording, merge pages or set canonicals. You can verify tags using the Canonical Tag Checker.
Yes to both. It is free, needs no account and has no stated word limit, though very long texts may be slow in your browser. The comparison runs on your device and the text is not sent to any server by this tool. That makes it fine for drafts. As always, avoid pasting confidential documents on a shared or public computer. If you work with client or unpublished material, check your own policy first, because the text stays in the open browser tab until you close or refresh it. Clearing both text boxes and closing the tab removes it from memory.