Overview
Rewriting is only half the job; the other half is proving what you rewrote. After a round of edits — yours, an editor's, a colleague's — someone will ask what moved, and scrolling through two long documents hoping to catch it all is a losing strategy. The human eye is excellent at reading and terrible at auditing, which is why this comparison is done by arithmetic instead of attention.
The tool breaks both texts into lines and finds the longest run of lines they still share, then flags everything else. Lines present only in the new version show as additions, lines gone from the old one show as removals, and the shared lines sit between them as context so each change makes sense where it happened.
How does a text comparison work?
Under the hood is a classic computer-science technique: the longest common subsequence. Imagine two stacks of index cards; the algorithm finds the biggest set of cards that appear in the same order in both stacks. Those become the “unchanged” backbone. Everything that had to be deleted to get from the first stack to the second is a removal; everything inserted along the way is an addition.
The result is exact rather than interpretive. A changed word means its whole line is reported as one removal plus one addition, which looks noisy on heavily rewritten paragraphs but is honest: it shows precisely what a person would have to do to turn version A into version B, keystroke by keystroke.
Features
- Line-by-line alignment using the longest-common-subsequence method, the same approach professional version-control systems rely on.
- Colour-coded changes with clear + and − markers, so additions and removals read at a glance.
- Context lines included, keeping each edit anchored in the surrounding text instead of floating alone.
- Live comparison that refreshes while you type or paste, plus a manual refresh when you want one.
- Change statistics counting added, removed and unchanged lines, with a clear note when nothing differs.
- Swap direction in one click to read the edit from new-to-old instead of old-to-new.
- Handles long documents without choking, all computed on your device.
Benefits
- Review edits in seconds. What took twenty minutes of careful scrolling becomes one look.
- Catch silent changes. A single altered word in a contract or price list cannot hide.
- Settle “what did you change?” with evidence instead of memory.
- Keep drafts private. Unpublished writing never travels to a server.
Who can use it
Editors and writers checking what a revision actually did before it ships. Lawyers and contract managers verifying that only the agreed clauses moved. Developers comparing config files or log output between two runs. Students seeing how their essay changed between drafts, and managers reviewing a report that passed through several hands — anyone who has ever asked “what changed here?” gets the answer in one paste.
How to use
- Paste the earlier version into the Original text box.
- Paste the revised version into the second box.
- Read the highlighted result as it appears — green for added, red for removed.
- Check the counts at the top for the size of the change.
- Use Swap to flip the direction if you want to read the edit backwards.
Frequently asked questions
Why does one changed word mark the whole line?
Because the comparison works line by line, not word by word. When any character in a line differs, the line is treated as removed from the old text and added in the new one. This is standard diff behaviour and keeps the output honest: it shows exactly which lines you would need to touch to transform one version into the other.
Can it compare more than two texts?
No — a diff is fundamentally a pairwise operation. To compare three versions, run the tool twice: old versus middle, then middle versus new. That chain actually tells a clearer story than a three-way merge, because you see each round of changes separately.
What counts as a “line”?
Anything separated by a line break. A paragraph with no internal breaks is one line, even if it wraps on screen. If your whole document pastes as a single line, the comparison will be less useful — breaking it into paragraphs first gives much better results.
Is there a size limit?
The comparison is plain arithmetic, so long documents are fine — full chapters, long contracts, big config files. Extremely large pastes may take a moment, but everything still happens locally in your browser tab.
Are my texts uploaded anywhere?
No. Both texts live only in the page's memory while you compare them. There is no upload step, no account, and nothing is stored — closing the tab discards everything.
What if the texts are identical?
The tool says so plainly instead of showing an empty result. The statistics will show zero additions and zero removals, which is itself useful confirmation — for example, that a file you expected to change actually did not.
Conclusion
Memory is unreliable and scrolling is slow; arithmetic is neither. Paste both versions, read the highlighted changes, and move on knowing exactly what moved — with your drafts never leaving your machine.