Duplicate Content Checker
Detect repeated sentences, duplicated lines and frequent phrases inside your own text, with an overall duplicate rate and highlighting. This is self-repetition checking — not comparison against the web — and runs entirely in your browser.
Between 0.6–0.9: lower catches more partially similar sentences, higher matches near-identical ones only
Paste text and click "Check now"; the report will appear here.
This tool checks self-repetition within your own text (identical or similar sentences appearing repeatedly). It does not compare against web content or databases and cannot replace academic plagiarism checkers.
How the duplicate rate is calculated
Checking runs on three levels: repeated sentences — after splitting on punctuation, identical sentences are flagged directly, and sentences of similar length are compared with character bigram similarity, which catches "a few words swapped" rewrites; duplicate lines — identical non-empty lines; the overall rate — the share of characters that belong to duplicated content.
The similarity threshold defaults to 0.8: sentences that are 80% similar count as duplicates. Lower it to 0.6 to catch heavier rewrites (with more false positives), or raise it to 0.9 to match near-identical sentences only. The highlighted preview marks every duplicate location in the original text for easy revision.
Good uses: finding repetitive filler in AI-generated or template copy, catching unintentional sentence repetition while writing, and cleaning duplicate lines from lists and data files. It is not a plagiarism checker — those compare your text against massive external databases, which is a different problem.
How to use
- Paste the text you want to check into the box above.
- Adjust the similarity threshold if needed, then click "Check now".
- Review the rate and the list, then fix the highlighted repetitions in your text.
FAQ
Can this replace a plagiarism checker?
No. Plagiarism checkers compare your writing against other people's work in literature databases; this tool only detects repetition inside your own text. The two are complementary: remove internal repetition here first, then run an academic checker for external similarity.
What duplicate rate is normal?
There is no absolute standard. Ordinary prose usually stays below 5%; lists and reference-style text naturally repeat more. Above 20%, check the highlights for long repetitive passages.
How are similar sentences detected?
Each pair of sentences is compared with character-bigram Jaccard similarity; pairs above the threshold (80% by default) count as duplicates. The method is robust to reordering and small word swaps, which makes it good at catching rephrased repetition.
Is my text uploaded?
No. Sentence splitting, similarity computation and highlighting all run locally in your browser with zero network requests; everything disappears when you close the page.