How does a text diff work?
A diff compares two versions of a text and works out the smallest set of changes that turns the first into the second. The usual approach is to find the longest sequence of items that both versions share, and treat everything outside that shared sequence as either removed from the original or added in the new version.
This tool does that comparison at the word level. It splits both texts into words and the whitespace between them, finds the longest common run, and marks the rest. Comparing words rather than whole lines is useful for prose, where an edit often changes a single word in the middle of a long line.
When comparing two texts is worth it
A diff answers the question "what actually changed?" without you having to read both versions side by side. It helps when you receive a revised contract clause or article draft and want to see exactly what an editor altered, when you suspect a copied paragraph was tweaked, or when you want to confirm that two configuration snippets differ in only the place you expect.
Writers use it to review their own revisions, and teams use it to check that a pasted block of copy matches the approved text. If you only want to alter specific words across a document, Find and Replace is a better tool than comparing manually.
How to compare two texts with this tool
- Paste the earlier version into the "Original text" box on the left.
- Paste the later version into the "Changed text" box on the right. Both boxes start with a sample sentence you can overwrite.
- Read the "Difference" panel below. Unchanged words appear normally, removed words are shown in red with a strike-through, and added words are shown in green.
- Edit either box and the comparison updates straight away. There is no compare button.
The result is a single combined view, not two columns, so read it from left to right as the story of how the original became the new text. There is no copy or download button, so use your browser's selection if you need to take the result elsewhere.
What to keep in mind about the results
Comparison is exact and case-sensitive. "Dog" and "dog" are different, and a word followed by punctuation is different from the same word without it, so "dog." and "dog" show up as a removal and an addition. Differences in spacing count too, because whitespace is compared along with words. If a result looks noisier than you expected, check for stray spaces, line breaks, or changed capitalization.
The method compares every word of one text against every word of the other, so very long texts can make the page slow to respond. For routine documents and drafts it is fine, but for huge files a dedicated code or document comparison tool may suit better. The comparison happens in your browser and nothing is uploaded.