Developer
Text Diff Checker
Compare two blocks of text and see exactly which lines and words changed.
Two versions of a contract, a config file, an essay draft — the question is always the same: what actually changed? Reading both documents line by line works until they are long, and then it stops working.
Paste both versions and the differences are marked for you: removed lines in red, added lines in green, unchanged lines left alone. Turn on word-level comparison and you get the changed words highlighted inside the changed lines, which is usually what you were squinting at. The comparison runs as a longest-common-subsequence pass in the tab, so the text never leaves the machine.
How to use it
- Paste the original text on the left and the edited version on the right. Line order matters, not formatting.
- Tick Ignore whitespace if indentation changed everywhere, or Ignore case if someone re-cased the file.
- Press Compare. The summary line tells you how many lines were added, removed and left alone.
- Choose a view: Side by side for the familiar two-column layout, Unified diff for the @@ format that patch tools use, or Change list for just the lines that differ.
- In unified view, set how many lines of context to keep around each change.
- Copy the result or download it as a .diff file for a code review.
Questions
Is my text sent anywhere?
No. Both blocks stay in the page and the comparison runs as JavaScript in your browser. You can disconnect from the network and it keeps working — which is the point, because diffs often contain contracts, keys and customer data.
What does the unified view do?
It produces the format used by the diff and patch tools: unchanged lines start with a space, removed lines with a minus, added lines with a plus, and skipped runs are replaced by an @@ marker. Use this view if you want to save the change as a file.
Why is there a line limit?
The comparison is quadratic in the worst case, so a 50,000-line pair would freeze the tab. The limit is 2,500 lines per side, which covers source files, contracts and articles comfortably.