Plagiarism detector that works entirely in your browser with no upload required. Paste two texts to find matching sentences with similarity scores, or switch to Originality Analysis mode to score a single text on vocabulary diversity, phrase repetition, and sentence structure. Free to use with no account needed.
The Plagiarism Checker offers two modes. Compare Two Texts places your original text and a suspected copy side by side and finds matching sentences using a word-set similarity algorithm (Jaccard similarity). Matching sentences are highlighted and listed with a similarity percentage, and an overall similarity score is shown from 0 to 100. A score below 20 is low similarity, 20-60 is moderate overlap, and above 60 is high similarity requiring review. Originality Analysis mode examines a single text and scores it on four dimensions: Lexical Diversity (how many unique words vs. total words), Phrase Uniqueness (absence of repeated 4-word phrases), Sentence Variation (variation in sentence lengths), and Boilerplate Score (absence of filler phrases like "in conclusion" or "it is important to note"). All analysis runs entirely in your browser with no data uploaded to any server. Plagiarism Checker is commonly used as a text similarity checker free, making it a practical choice for comparing documents directly in the browser. For complete results, Grammar Checker can check grammar, spelling, and style in any text, Text Diff Checker can show character-level differences between two texts, and Paraphrasing Tool can rewrite text in a different tone or style.
Text similarity detection is a well-studied area of natural language processing. The Jaccard similarity coefficient used here is one of the simplest and most interpretable approaches: it measures the intersection of two word sets divided by their union. This makes it robust to word order changes but sensitive to vocabulary overlap. More sophisticated systems like TF-IDF cosine similarity weight words by their rarity across a document corpus, making them better at ignoring common filler words. Transformer-based semantic similarity models (like those used in Turnitin's latest engine) can detect paraphrasing even when no words are shared, by comparing sentence meaning in high-dimensional vector space. For the purpose of this tool, Jaccard similarity provides an easily understood, transparent measure that works well for detecting sentences that have been copied with minor modifications. The Originality Analysis metrics are drawn from computational stylometry research: lexical diversity (also called Type-Token Ratio) is a classic readability and originality measure. Very low lexical diversity is characteristic of AI-generated text and of text with excessive repetition. Unusual sentence length uniformity (very low coefficient of variation) is another marker observed in certain types of generated or templated text, as human writers tend to vary their sentence lengths naturally. Boilerplate phrase detection targets phrases that are semantically empty and appear across many pieces of writing, particularly in academic contexts where students pad word count with transitional filler.