How does the free plagiarism checker work?

It uses Jaccard similarity on individual sentences and 4-word n-gram (shingle) fingerprinting to detect both direct copying and paraphrased content between two documents.

Is my text sent to any server?

No. All analysis runs entirely in your browser. Your documents are never uploaded or stored anywhere.

What similarity percentage is considered plagiarism?

Generally, under 20% is considered original, 20–50% shows some similarity that may be acceptable, 50–75% is high similarity and warrants review, and above 75% is likely plagiarized.

Can it detect paraphrased content?

Yes. The Jaccard algorithm compares word sets, not exact strings, so it can identify paraphrased sentences where different words are used to convey the same meaning.

What is the n-gram fingerprint feature?

It counts matching 4-word phrases (4-grams or shingles) across both documents. A high count of common 4-word phrases indicates structural similarity even if individual sentences differ.

Does it work with non-English text?

The algorithm is language-agnostic and will work with any language, though the stopword filtering is optimized for English.

What is the minimum text length required?

Each text should contain at least a few complete sentences (5+ words each) for the sentence-level analysis to be meaningful.

Can I check a student essay against an article?

Yes. Paste the essay on the left and the article on the right. The tool will identify which sentences have high overlap.

Plagiarism Checker

Compare two documents to detect copied or paraphrased content. Paste your text and a reference document: all processing happens in your browser.

Your Text

0 words

Reference Text

0 words

Free online plagiarism checker: detect copied and paraphrased content

Plagiarism detection tools typically require subscriptions, API keys, or account registration. This free browser-based checker lets you compare any two documents instantly without sending your text to any server. It uses Jaccard similarity: a set-theoretic measure that compares the overlap in unique words between two sentences: combined with 4-gram shingle fingerprinting for a two-layered analysis.

Sentence-level scoring flags individual sentences with a similarity percentage, making it easy to pinpoint exactly which parts of your document overlap with the reference. The 4-gram fingerprint count gives an additional document-level signal: a high number of shared 4-word phrases is a strong indicator of structural copying even when words have been slightly rearranged. Use this tool for academic integrity checks, content audits, and verifying that rephrased articles are sufficiently distinct.

Step-by-step guide

1
Paste your text
Enter the text you want to check in the left panel. Use the Load sample button to try a demo.
2
Paste the reference document
Add the reference or source text in the right panel: this is what your text will be compared against.
3
Click Check Similarity
The tool analyzes both texts using Jaccard similarity on a sentence level and reports a percentage.
4
Review the similarity score
See an overall similarity percentage with a color-coded label: Original, Some Similarity, High Similarity, or Likely Plagiarized.
5
Inspect matched sentences
Scroll down to see which specific sentences were flagged as similar and their reference matches.

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Frequently Asked Questions

How does the free plagiarism checker work?: It uses Jaccard similarity on individual sentences and 4-word n-gram (shingle) fingerprinting to detect both direct copying and paraphrased content between two documents.
Is my text sent to any server?: No. All analysis runs entirely in your browser. Your documents are never uploaded or stored anywhere.
What similarity percentage is considered plagiarism?: Generally, under 20% is considered original, 20–50% shows some similarity that may be acceptable, 50–75% is high similarity and warrants review, and above 75% is likely plagiarized.
Can it detect paraphrased content?: Yes. The Jaccard algorithm compares word sets, not exact strings, so it can identify paraphrased sentences where different words are used to convey the same meaning.
What is the n-gram fingerprint feature?: It counts matching 4-word phrases (4-grams or shingles) across both documents. A high count of common 4-word phrases indicates structural similarity even if individual sentences differ.
Does it work with non-English text?: The algorithm is language-agnostic and will work with any language, though the stopword filtering is optimized for English.
What is the minimum text length required?: Each text should contain at least a few complete sentences (5+ words each) for the sentence-level analysis to be meaningful.
Can I check a student essay against an article?: Yes. Paste the essay on the left and the article on the right. The tool will identify which sentences have high overlap.

AlteredIdea vs alternatives

vs Google Docs / Word: Purpose-built tool, instant results, no account.

vs browser extensions: No install, no permissions, works on any device.

vs paid SEO tools: Completely free, unlimited use.

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