How does this diff tool work?

It tokenises each side into words or characters and computes the longest common subsequence between them. Tokens only in the original are marked removed, tokens only in the modified text are marked added, and shared tokens are unchanged.

What is the difference between word and character mode?

Word mode compares whole words and whitespace, which reads cleanly for prose and paragraphs. Character mode compares every character, which is better for short strings, codes, or spotting single-letter typos.

What is a unified diff?

A unified diff is the standard patch format used by tools like git. Lines starting with - were removed, lines starting with + were added, and unchanged lines start with a space. You can copy it here to share or apply elsewhere.

Is my text uploaded anywhere?

No. The entire comparison runs in your browser using JavaScript. Your text never leaves your device, which makes the tool safe for confidential documents.

Can it compare large documents?

It works well for typical documents and code snippets. Because the algorithm compares every token against every other token, extremely large inputs (tens of thousands of words) will be slower, so trim to the relevant sections for best speed.

Text Diff (Inline & Side-by-Side)

A text diff highlights exactly what changed between two versions of a document — which words were added, which were removed, and which stayed the same. This free tool compares two blocks of text directly in your browser and shows the result inline with colour highlighting, plus a copy-ready unified diff for sharing.

How it works

The tool first splits each side into tokens. In word mode it splits on whitespace (keeping the spaces so formatting is preserved); in character mode it splits into individual characters. It then computes the longest common subsequence (LCS) between the two token lists — the longest ordered set of tokens that appears in both.

Walking that LCS table from start to finish produces three kinds of token:

equal — present in both, shown plainly.
remove — present only in the original, shown red and struck through.
add — present only in the modified text, shown green.

This is the same core idea behind git diff and most code-review tools.

Tips and example

Use word-level for essays, emails, and contracts so whole edited words light up rather than scattered letters.
Use character-level to catch a single transposed digit in a reference number or a one-letter typo.
The summary line shows counts like +3 added · -2 removed, a quick way to gauge how big a change is.

For example, comparing The quick brown fox with The quick red fox marks brown as removed and red as added, while The, quick, and fox stay unchanged. Copy the unified diff and you will see -brown and +red lines you can paste into a code review or change log.