Text Diff Checker

How It Works

When a document goes through revisions, the important question is usually not what the new version says but what changed. This tool answers that by comparing the two texts word by word, using the longest-common-subsequence method: it finds the longest run of words that appear in both versions in the same order, and treats everything else as added or removed. Words only in the new text are highlighted green; words that disappeared are highlighted red with a strikethrough; unchanged words are left plain.

The comparison is word-based rather than character-based, which makes it far easier to read: a changed word shows up as one red word and one green word, instead of a jumble of changed letters. Whitespace differences are ignored, so re-wrapping a paragraph does not show up as a change. The comparison runs entirely in your browser, so contracts, essays and private drafts never leave your device.

Worked Example

Compare the original The quick brown fox jumps over the lazy dog. with the new version The quick red fox jumps over the lazy cat. The result highlights brown and dog. in red as removed, and red and cat. in green as added. The counts read: 2 words added, 2 words removed, 7 words unchanged. Change only one word — brown to red — and the counts become 1 added, 1 removed and 8 unchanged.

How to Use This Tool

Paste the original text in the first box and the new version in the second, then press Compare Texts. The merged view below shows both versions combined, with additions in green and removals in red, and the table underneath gives the exact counts. Press Swap if you pasted them in the wrong order. Texts over about 3,000 words each are rejected, because the comparison would take too long to run in the browser.

Tips and Practical Advice

• Compare one section at a time for long documents. A chapter-by-chapter comparison is easier to review than a single wall of highlighted text.
• Remember punctuation sticks to words. dog. and dog count as different words, so a sentence that only gained a full stop shows up as one word removed and one added.
• Use it before sending a revision. A quick diff catches accidental deletions and stray edits before a client or a teacher sees them.