When you have two versions and want parts of each, compare them and merge change by change. The arrow buttons between the columns copy a change to the other side; both text boxes stay editable for anything else. Undo works as you'd expect, and the merged result downloads with the original line endings.
How to merge two texts
- Paste both versions into the left and right boxes.
- Copy the changes you want with › (to the right side) or ‹ (to the left side) on each change, or Use original / Use changed in the unified view.
- Edit freely in either box; the comparison updates as you type.
- Download the result with Export → Download changed text (or original text).
Why Diffspot
- Change-by-change mergingAccept or reject each change with one click, in either direction.
- Native undoEach merge can be undone from the notification or with Ctrl/⌘+Z in the text box.
- Nothing is uploadedThe comparison runs in this browser tab, in WebAssembly. Your text and files are never sent to a server, not even ours, and nothing is saved.
- Fast on big inputsThe diff engine is written in Rust and runs in a background thread, so typing stays smooth. Files with hundreds of thousands of lines compare in about a second.
- Free, no accountEvery feature is free with no sign-up and no size paywall. Ads pay for the site, and they run in an isolated frame that can't read the page.
- Works offlineAfter your first visit the app is cached, so it keeps working on a plane or behind a strict firewall.
Frequently asked questions
Is this a three-way merge?
No, it's a two-way merge: you see two versions and choose, per change, which one to keep.
Is it safe to paste confidential text or files?
Yes. Diffspot computes every comparison on your device: the page loads the engine once, then your text and files stay in the browser tab. There is no upload and no server-side storage, and ads are shown in a separate sandboxed frame that cannot read the page. How Diffspot works explains the details, and you can confirm it in your browser's network panel.
Can I share a comparison?
Yes. Share creates a link that contains both texts, compressed into the part of the URL after #. Browsers never send that part to a server, so the link works without uploading anything. Anyone with the link can read the texts, so share it like you would share the texts themselves.