What actually changed between these two versions?
Two versions of a contract arrive and “only minor edits” needs verifying. The config file worked Tuesday and broke Friday. The agency returned your copy “with small tweaks”. Eyeballing two texts for differences is the task human attention is worst at — studies on proofreading consistently show we read what we expect, not what's there. Diffing automates the comparison: paste both versions, click, and every changed line is highlighted — green for added, red struck-through for removed — with a summary count.
How to compare two texts
- Paste the original (older) text into the left box.
- Paste the changed (newer) text into the right box.
- Click Compare.
- Read the unified result: unchanged lines in grey context, removals in red, additions in green, with totals above.
Reading a diff like a reviewer
The output interleaves both versions in reading order, which makes edits appear as a red line (the old wording) immediately followed by a green line (the new wording) — read those pairs together to judge each change. Blocks of pure green are new content; pure red blocks are deletions; and the grey context around them tells you where in the document you are. The summary counts are your first smell test: “3 added, 3 removed” suggests honest tweaks, while “41 removed” in a contract review is a finding all by itself.
The line-based fine print
This is a line-level diff — the unit of comparison is the whole line, the same standard used by version-control systems. Change one word in a paragraph that's stored as a single long line, and the diff faithfully reports that whole line as changed (old red, new green); spotting the word within it is then a one-line task instead of a forty-page one. For prose where you want finer granularity, a trick: break the text into one-sentence-per-line first (find “. ” replace with “.\n” in our Find & Replace tool) and diff those — sentence-level changes light up individually.
Where diffing earns its rent
- Contract redlines: verify the counterparty's “minor changes” claim in seconds, independently of their tracked changes.
- Config drift: working vs broken settings file — the breakage usually lives in the red/green lines.
- Editorial rounds: see exactly what an editor or AI rewrite touched.
- Data validation: two exports that “should be identical” — confirmed or refuted instantly.
Both texts stay in your browser — confidential agreements diff as privately as they'd sit in a drawer. Paste, compare, know.
Quick reference
| Property | Detail |
|---|---|
| Input | Two texts, side-by-side boxes |
| Algorithm | Line-based LCS (version-control standard) |
| Output | Unified view: red removed, green added, grey context |
| Summary | Added/removed line counts |
| Granularity tip | Pre-split prose into sentence lines for finer diffs |
| Size | Hundreds of pages compare instantly |
| Processing | 100% in-browser, no upload |
Frequently asked questions
Why does changing one word highlight the whole paragraph?
The diff compares line by line, and a paragraph stored as one long line changes as a unit. The red/green pair shows old and new versions adjacent — or pre-split text into sentence-per-line with Find & Replace for word-level precision.
Which text goes in which box?
Convention: original/older on the left, changed/newer on the right. Then red = what the new version removed, green = what it added. Swapping boxes simply inverts the colours.
Can I diff confidential contracts safely here?
Yes — comparison runs entirely in your browser memory. Neither text is transmitted, stored or logged anywhere. It's as private as reading the documents on your own screen.
Does it detect moved paragraphs?
A moved block appears as removed in its old position and added in its new one — standard diff behaviour. The counts still reconcile; just recognise the matching red and green blocks as a move, not an edit.