Text Compare

Paste the original on the left and the changed version on the right. Removed text is shown in red and added text in green, so you can see exactly what changed between two drafts, answers or lists.

How to compare two texts

1. Paste the original text in the left box and the new version in the right box.
2. Choose word by word (best for edited sentences) or line by line (best for lists and code).
3. Press Compare. Deleted text is red and crossed out; added text is green. The similarity score shows how much the two versions share.

How the comparison works

The tool finds the longest common subsequence: the longest list of words (or lines) that appear in both texts in the same order. Everything in that list is unchanged; whatever is left over in the original was removed and whatever is left over in the new text was added. The similarity score is 2 × unchanged ÷ (words in both texts) × 100%.

Uses for students and teachers

• Check what changed between two drafts of an essay.
• Compare a student’s answer with a model answer.
• Spot the one different line in two lists, data files or pieces of code.

Comparison happens in your browser, so private text never leaves your device.

Text comparison practice questions

Test yourself with 6 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

How do I find the difference between two texts?

Paste both versions and press Compare. Additions are highlighted in green and deletions in red, word by word or line by line.

Is my text uploaded anywhere?

No. The comparison runs entirely in your browser, so nothing you paste is sent to a server.

What does the similarity percentage mean?

It is twice the number of unchanged words (or lines) divided by the total in both texts. Identical texts score 100%.

Why does a moved sentence show as removed and added?

The method keeps words in their original order, so text that changes position counts as deleted in one place and inserted in another.

Sources

• Hunt and McIlroy: An algorithm for differential file comparison (Bell Labs)
• Wikipedia: Longest common subsequence

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