Overview
Edits are easy to make and hard to audit. A colleague returns a contract with “just a few tweaks,” a writer submits draft seven, a config file behaves differently than yesterday — and the question is always the same: what exactly moved? Reading both versions end to end is slow and unreliable; the eye skips, the mind fills in. This tool replaces attention with arithmetic.
Both texts are split into lines and aligned by their longest shared subsequence, the same family of algorithm that powers version-control systems. Lines only in the new text appear as additions, lines missing from it as removals, and the unchanged lines between them provide context so every change reads in place.
How does the comparison actually work?
Think of each text as a stack of numbered cards. The algorithm finds the largest set of cards that appear in the same order in both stacks — the longest common subsequence. Those cards are the unchanged backbone. Everything else is an edit: cards present in the old stack but not the new are removals; cards in the new but not the old are additions. The result is the minimal, exact set of changes between the two versions.
It is exact rather than clever. A single altered word marks its whole line as changed, because the comparison works line by line. That can look noisy on heavily rewritten paragraphs, but it is honest: it shows precisely which lines someone would have to touch to turn version A into version B.
Features
- Line-by-line alignment via longest-common-subsequence, the method version control relies on.
- Clear +/- markers with colour coding so additions and removals read at a glance.
- Context lines keep each change anchored in surrounding text.
- Live results that refresh as you type or paste.
- Change counts — added, removed and unchanged lines, tallied automatically.
- Swap button to read the edit in the opposite direction.
- Handles long documents — chapters, contracts and configs — on your device.
Benefits
- Review in seconds what took twenty minutes of scrolling.
- Catch quiet changes — one altered figure in a price list cannot hide.
- Answer “what changed?” with evidence instead of memory.
- Keep drafts private — unpublished text never touches a server.
Who can use it
Editors verifying what a revision actually did, lawyers confirming only agreed clauses moved, developers comparing configs or logs between runs, students tracking how an essay evolved, and managers reviewing documents that passed through several hands. Anyone who has ever been told “I only changed one thing” and wanted proof will use this weekly.
How to use
- Paste the earlier version into the Original text box.
- Paste the revised version into the second box.
- Read the highlighted result — additions and removals marked line by line.
- Check the counts for the overall size of the change.
- Use Swap to flip the comparison direction if useful.
Frequently asked questions
Why is a whole line flagged when only one word changed?
Because the unit of comparison is the line. Any difference within a line makes it count as removed from the old text and added in the new one. This is standard diff behaviour across the industry, and it keeps the output truthful about which lines you would need to edit to convert one version into the other.
Can I compare three versions at once?
Not in one pass — comparison is inherently a pairwise operation. Run the tool twice instead: old against middle, then middle against new. The chain is actually more informative than any three-way view could be, because each round of edits appears on its own instead of tangled with the others, and you can attribute every change to the draft that introduced it.
My document pasted as one giant line. Now what?
Break it into paragraphs before pasting. The tool aligns text line by line, so a single-line paste produces a single changed line and almost no insight. Splitting on paragraphs — or even sentences — first gives the algorithm the structure it needs, and the resulting comparison becomes dramatically more useful.
Is there a practical size limit?
Only the memory in your browser tab. Full chapters, long contracts and large configuration files compare without complaint; genuinely huge pastes may take a moment while the table fills in. Because everything runs locally, there is no server to time out and no upload that could stall halfway.
Are my texts uploaded?
No. Both versions live only in the tab's memory for the duration of the comparison. There is no upload step, no account holding your documents and nothing written to disk — closing the tab discards both texts completely, which matters when the drafts are not yet public.
Conclusion
Trust arithmetic over attention. Paste both versions, read the marked changes, and know exactly what moved — with your documents never leaving your machine.