Plagiarism Checker

Free plagiarism checker that compares your text with sources you provide: similarity score, copied and paraphrased passages highlighted. Private, in-browser.

Analysed in your browser: your text and images are never uploaded.
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Compares your text only with the sources you add here; it does not search the internet.

How to compare texts for plagiarism

  1. Paste the text you want to check into Your text, or click Upload file to load a .txt, .pdf or .docx document.
  2. Paste a source into Source 1: an article, a classmate's essay, an earlier version of the text. Each source box has its own Upload link.
  3. Fill in Source 2 if you have one, and click Add another source for more, up to 8 in total.
  4. Leave Also detect paraphrasing ticked to find reworded sentences as well as copied ones. The first time, this downloads a 23 MB language model, which your browser then caches.
  5. Click Compare texts and read the similarity score, the highlighted text and the list of matching passages.

All texts stay in your browser. Nothing is uploaded or stored, and none of your documents is added to a database.

What this checker does, and does not do

This is a comparison tool. It compares your text with the sources you add and with nothing else. It does not search the internet, and it does not check against a database of essays or publications. If you suspect a text was copied but do not know from where, find the likely source first, for example by searching the web for an unusual sentence in quotation marks, then paste it here.

That makes it a good fit for situations where you already have the texts:

  • a teacher comparing an essay with a suspected source, or two students' essays with each other;
  • a writer checking that an article has not stayed too close to the sources used for research;
  • an editor or client checking whether a "rewritten" text is really new or only lightly reworded;

How matching works

Identical wording. Both texts are split into words, ignoring case and punctuation, and every sequence of 5 consecutive words in your text is looked up in each source (4 words when your text is very short). Every shared sequence is highlighted in the colour of the source it came from, so with several sources you can see which part matches which.

Paraphrasing. Changing a few words defeats exact matching, so the tool also compares meaning. Each sentence of your text that is not already mostly copied is turned into a sentence embedding with the all-MiniLM-L6-v2 model and compared with every sentence in your sources. When the cosine similarity reaches 0.75 or more, the sentence counts as paraphrased. Paraphrased sentences have a dotted underline; hover over one to see the source sentence it resembles and the similarity.

Reading the result

The similarity score is the share of your text that matches: the words in identical sequences plus the words in paraphrased sentences, divided by the total number of words. Below it you see the identical-wording percentage and the number of paraphrased sentences, both for all sources together and for each source separately. Longest matching passages lists copied runs of 8 or more words, which are the strongest evidence of direct copying.

There is no universal cut-off for plagiarism. A literature review with correctly cited quotes can score high, while an essay with one unattributed paragraph scores low. Look at what matches, not only how much.

When a match is not plagiarism

  • Quotations with proper citations are legitimate, even though they match word for word.
  • Common phrases such as "at the end of the day" or "on the other hand" can match by chance, especially with the shorter 4-word sequences.
  • Technical terms, names and titles must be written the same way in every text.
  • Sentences on the same topic can be close in meaning without being copied. Treat a single paraphrase match as a hint and a long run of them as a pattern.

Tips

  • Add every relevant source in one run instead of checking them one by one. Each source keeps its own colour, and wording shared by several sources is counted only once.
  • If a PDF imports with broken lines or missing text, convert it with PDF to Text first. Scanned PDFs need OCR before they contain any text.
  • Need to know whether an essay was written with AI rather than copied? Use the AI Detector; AI text is usually new wording and will not show up here.
  • Checking the references in a document is a different job: the AI Hallucination Checker confirms that cited sources exist.
Tip: To check whether a student's two essays share material, paste the newer one as your text and the older one as a source. Reused paragraphs show up immediately.

Frequently asked questions

Does it search the internet for copied text?

No. It only compares your text with the sources you paste or upload. To find an unknown source, search the web for a distinctive sentence first.

Can it detect paraphrasing?

Yes, when the paraphrase is close to a sentence in one of your sources. It compares sentence meaning with a small language model and flags sentences with a similarity of 0.75 or more. Heavily restructured text, or ideas spread across several sentences, can still slip through.

Are my documents stored or added to a database?

No. The comparison runs in your browser, and neither your text nor your sources are uploaded.

What similarity score counts as plagiarism?

There is no fixed threshold. Check whether the matching passages are cited quotations, common phrases or unattributed copying; that decides it, not the percentage.

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