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Plagiarism Checker

Detect duplicate sentences and repeated phrases in your text. Highlights exact matches and near-duplicates with similarity scores — no account or upload required.

Exact duplicates Near-duplicates Similarity score Sentence-level n-gram analysis Instant results
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Free · No credit card · 50 credits/day

What the checker detects

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Exact copy-paste

Sentence-level exact match detection highlights any sentence that appears more than once, with the line numbers of each occurrence.

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Near-duplicates

Bigram Jaccard similarity detects paraphrased sentences — even when synonyms are swapped or word order is changed.

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Similarity score

Every flagged pair gets a percentage similarity score so you can triage — 95% is copy-paste, 60% may be coincidental overlap.

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Phrase repetition

Finds repeated trigrams and phrases within the same document — useful for spotting overused filler phrases or accidental repetition.

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Cross-document check

Paste a second document or source text to compare against — ideal for checking student work against a reference or your own previous draft.

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Instant, client-side

Analysis runs entirely in your browser. No text is ever sent to a server — important for sensitive academic or legal documents.

Frequently asked questions

What counts as plagiarism?

Plagiarism is presenting someone else's work without attribution. It includes: direct copy-paste without citation, paraphrasing without credit, self-plagiarism (reusing your own previously published work), and mosaic plagiarism (mixing copied phrases with original writing). Even if accidental, it carries the same academic and professional consequences.

How does the plagiarism checker work?

The checker splits text into sentences and n-grams, then compares them against themselves and any reference text you provide. Exact duplicates are flagged at 100% similarity. Near-duplicates are detected using Jaccard similarity on bigrams — a score above a configurable threshold triggers a warning.

What is the difference between plagiarism and paraphrasing?

Legitimate paraphrasing restates someone's idea in your own words AND includes a citation. Plagiarism is paraphrasing without that citation, or paraphrasing so closely that only a few words are changed (mosaic/patchwork plagiarism). Good paraphrase involves genuinely restating the idea in a different structure — not just swapping synonyms.

Can I use this to check a document for self-plagiarism?

Yes — paste your new document and compare against your previous work. Self-plagiarism (reusing published content without disclosure) is an ethical violation in academic publishing and some journalism contexts. This tool identifies substantial overlap before you submit.

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