Text Similarity Checker

Compare two texts and calculate similarity percentage. Highlights matching phrases using n-gram analysis. Compares your two texts against each other — does not search the web.

Related Tools

How to Use

1. Enter Two Texts — Paste the source text in the left panel and the text you want to compare in the right panel. Both texts should be at least a few sentences long for meaningful analysis.
2. Choose N-Gram Size — Select the n-gram size: 3-word phrases (default, good for general comparison), 4-word (stricter matching), or 2-word (catches more but may flag common phrases). Then click Check Similarity.
3. Review the Results — The similarity score shows overall percentage with a color-coded rating. Matching phrases are highlighted in yellow in both texts so you can see exactly which parts overlap. Stats show n-gram counts and match details.

About the Text Similarity Checker

WritePadPro's Text Similarity Checker compares two texts and calculates a similarity percentage based on n-gram matching — a well-established computational linguistics technique used in academic plagiarism detection, content analysis, and natural language processing research.

Important: What This Tool Does and Does Not Do

This tool compares two texts that you provide against each other. It does NOT search the internet, query academic databases, or check against any external content. It answers the question: "How similar are these two specific texts?" — not "Was this text copied from somewhere online?" For web-based plagiarism detection, you would need a service with a crawled index of web content, which requires server infrastructure beyond the scope of a client-side tool.

N-Gram Matching Algorithm

The algorithm works by extracting all possible sequences of N consecutive words (n-grams) from both texts. For example, with n=3, the sentence "the cat sat on the mat" produces four trigrams: "the cat sat", "cat sat on", "sat on the", and "on the mat." The tool then computes the Jaccard similarity coefficient: the number of n-grams that appear in BOTH texts divided by the total number of unique n-grams across both texts. This produces a score from 0% (no overlap) to 100% (identical).

Choosing N-Gram Size

• 2-word n-grams (bigrams) — Catches the most matches, but may flag common two-word combinations ("in the", "it is") as matches even when texts are unrelated. Best for very short texts.
• 3-word n-grams (trigrams) — Default. Good balance between sensitivity and specificity. Three-word sequences are unlikely to match by coincidence unless actual content overlap exists.
• 4-word n-grams — Stricter matching. Only flags longer shared phrases. Reduces false positives from common language patterns. Best for longer texts or when you want high-confidence matches only.
• 5-word n-grams — Very strict. Only near-verbatim copying of 5+ consecutive words registers as a match. Best for detecting direct copying in long documents.

Phrase Highlighting

After computing similarity, the tool highlights the matching n-gram positions in both texts with a yellow background. This visual overlay shows you exactly which parts of the texts overlap. You can see whether the matching content is concentrated in one section (suggesting a copied paragraph) or distributed throughout (suggesting shared source material or common topic vocabulary).

Use Cases

• Students — Check if your paraphrase is sufficiently different from the source material before submitting
• Educators — Compare two student submissions to check for unauthorized collaboration
• Writers — Verify that your rewrite of existing content is original enough
• SEO professionals — Check content uniqueness across multiple pages on your site
• Legal teams — Compare contract versions or check content for unauthorized reproduction

Privacy

The n-gram extraction and Jaccard similarity calculation run entirely in your browser. Both texts stay on your device — they are never transmitted to any server, stored in any database, or indexed in any way. This is critical for sensitive content: academic papers under review, proprietary business documents, legal materials, and any text where confidentiality matters.