AI Plagiarism Checker — free online duplicate content & paraphrase detector
Paste your original text on the left and a suspect text on the right. Our AI compares them sentence by sentence using Universal Sentence Encoder embeddings, classic Jaccard / cosine / edit-distance metrics, and rewriting-pattern analysis — then highlights every copied or rephrased passage and exports a report. No upload, no signup, runs in your browser.
Detecting copying & paraphrasing…
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Run a check to see the verdict.
When to run a plagiarism check
Compare two texts when you need to know whether one was copied, paraphrased or rewritten from the other — works for essays, articles, blog posts, papers and AI-generated content.
Check student essays
Spot direct copying and paraphrasing in homework, assignments and exam submissions.
Verify article originality
Compare a draft against an existing article to confirm originality before publishing.
Find content scrapers
Check if a competitor or scraper site is reusing your blog posts with light edits.
Detect AI rewrites
Catch tools that "spin" your content with synonym swaps and word-order changes.
Audit your own writing
Compare a draft to your source notes to make sure you've paraphrased enough.
Build a copyright case
Document sentence-level matches and export a report for legal or DMCA workflows.
How to check plagiarism online (4 steps)
Paste the original text
Drop your own article, essay, paper or source content into the Original Text editor on the left.
Paste the suspect text
Paste the text you suspect may have copied or paraphrased your content into the Suspect Text editor on the right.
Run the check
Click Check plagiarism. The AI runs six stages — cleaning, topic, semantic, copy patterns, rewrite detection and final report — in seconds.
Review & export
Inspect per-sentence matches, rephrasing patterns and all detection metrics. Export a TXT or HTML/PDF report when you need evidence.
Frequently asked questions
An AI plagiarism checker uses natural language processing and sentence embeddings to compare two texts and detect copying, paraphrasing and rewriting. HCODX's checker uses the Universal Sentence Encoder to score sentence-level semantic similarity in addition to classic Jaccard, cosine and edit-distance metrics.
Yes. The HCODX AI Plagiarism Checker is 100% free, ad-free, and does not require signup or login. There are no daily limits or paywalls.
No. Both texts stay in your browser. Comparison runs locally with TensorFlow.js and the Universal Sentence Encoder. The model is downloaded once and cached, after which the tool works offline.
Yes. Sentences with 60–92% similarity are analyzed for rewriting patterns including word-order changes, synonym replacement, length variation and active/passive voice flips. Sentences above 92% are classified as direct copying.
Sentence-embedding similarity is far more robust than word-overlap matching — it detects paraphrasing that classic checkers miss. The tool combines multiple metrics (semantic, topic, structural, coverage, Jaccard, cosine, edit distance) into a weighted score with confidence levels.
Yes. Copy the text out of the PDF or essay (Cmd/Ctrl+A then Cmd/Ctrl+C) and paste it into the Original or Suspect editor. The tool treats it like any other text input.
95–100% indicates near-identical copying. 90–95% is direct copying with minor edits. 85–90% is plagiarism by light rephrasing. 75–85% is heavier rephrasing. 60–75% indicates systematic rewriting. Below 50% generally means original content with at most isolated similarities.
Yes. After each run you can export a clean HTML report (printable to PDF) or a plain-text report listing per-sentence matches, severity, all detection metrics and an executive summary.
About this AI plagiarism checker
HCODX's AI Plagiarism Checker is a free, ad-free, no-signup tool that compares two texts and detects copying, paraphrasing and systematic rewriting directly in your browser. It runs on top of TensorFlow.js and the Universal Sentence Encoder — nothing is uploaded.
How the score is built
- Sentence-level matches — each suspect sentence is embedded and compared to every original sentence; structural penalties handle large length and word-count differences.
- Topic similarity — embeddings on extracted key terms.
- Semantic similarity — embeddings on stop-word-stripped content.
- Coverage — share of original chunks with a strong match in the suspect text.
- Structure — paragraph counts and average chunk-length similarity.
- Classic metrics — Jaccard set overlap, cosine of term-frequency vectors, normalised Levenshtein distance.
Score bands
95–100%— direct copying, almost identical text.90–95%— direct copying with light edits.85–90%— plagiarism by minor rephrasing.75–85%— heavier rephrasing.60–75%— systematic rewriting / "spinning".50–60%— partial reuse / similar topic.< 50%— generally original.