Compare two texts and see every change
Spotting the difference between two versions of a document by reading them side by side is slow and unreliable — the eye skips over small edits buried in long paragraphs. This free text diff checker does the comparison for you: paste the original in one box and the revised version in the other, and every added, removed and unchanged line is highlighted instantly. It works entirely in your browser, so nothing you paste is ever uploaded.
Why line-by-line comparison beats reading manually
Humans are bad at noticing what did not change and good at noticing what draws attention — which is exactly backwards from what proofreading a revision needs. A diff algorithm has no such bias: it mechanically finds the smallest set of edits that turns one text into the other, so a single swapped word in a long paragraph is caught exactly as reliably as a whole rewritten section.
How the diff algorithm works
Under the hood, the checker looks for the longest common subsequence of lines shared by both texts — the largest set of lines that appear in the same relative order in each version. Everything in that shared sequence is treated as unchanged context; everything else is either something that was removed from the original or something new that was added in the revision. This is the same core idea used by git diff and every major version-control system, which is why the output will feel familiar if you have ever reviewed a code change.
Where a diff checker helps
- Code review — comparing a snippet before and after a refactor without switching to git.
- Contract and document redlines — confirming exactly what changed between two drafts.
- Content editing — checking what an editor altered in a blog post or article.
- Translation QA — comparing two versions of a translated string for accidental drift.
How to use it
Paste the original text on the left and the updated text on the right. The comparison updates as you edit either side, with additions and removals highlighted so you can review a large change in seconds instead of scanning line by line yourself.
Diffing is a habit worth building
Developers reach for git diff constantly, not because every change is complicated, but because a computer catching a one-character typo is more reliable than a human proofreading a wall of text. The same habit pays off outside code: before sending a revised contract, publishing an edited article, or approving a translated string, running it through a diff takes a few seconds and removes any doubt about exactly what changed — no matter how small.
Frequently asked questions
How does the diff checker decide what changed?
It compares the two texts line by line using a longest-common-subsequence algorithm, the same principle behind tools like git diff, to find the smallest set of additions and removals that explains the difference.
Is my text uploaded anywhere?
No. The comparison runs entirely in your browser, so both pieces of text — including confidential drafts or proprietary code — stay on your device.
Can I compare source code, not just prose?
Yes. The comparison works on any plain text, so code files, config files and log output compare just as well as articles or contracts.
What do the colors in the result mean?
Lines only in the first text are marked as removed, lines only in the second text are marked as added, and unchanged lines appear as plain context in between.