Is it safe to use the Diff Checker online?

Yes — and ours is safer than most. Many free online tools quietly upload your files to their servers to do the work. We don't. Everything happens inside your browser on your own device, so your files never reach the internet. There's no upload step, no server copy, and no way for us (or anyone else) to see what you're working on.

Are my files uploaded to a server?

No. There's no server-side processing here. The whole tool is a tiny app that runs in your browser — we don't even have a server that could receive your files. You can confirm this by opening your browser's network tab while you use the tool: nothing leaves your device.

Do I need to sign up or pay?

No. There's no account, no email collection, no credit card. The tool is free to use as much as you want, on as many files as you want. We're supported by a few unobtrusive ads on the page — not by your data.

Is this a word-level or line-level diff?

Line-level using LCS. For word-level diff inside changed lines, use a dedicated tool — that's on the roadmap.

Will huge files work?

Diff is O(n*m) so multi-megabyte files get slow. For source code, you're fine.

Diff Checker

Spot the differences between two versions of any text. Line-by-line diff with added (green) and removed (red) highlighting. Useful for code reviews, legal-document comparison, and edit history.

Features

Side-by-side or unified diff view
Line-level adds, removes, and changes
Whitespace-only changes optional ignore
Stats: lines added, removed, changed
Copy unified diff in standard patch format

How to diff checker

Paste both versions — Original on the left, modified on the right.
Read the diff — Added lines highlight green, removed red.
Toggle settings — Ignore whitespace, switch view modes.

Frequently asked questions

Is it safe to use the Diff Checker online?: Yes — and ours is safer than most. Many free online tools quietly upload your files to their servers to do the work. We don't. Everything happens inside your browser on your own device, so your files never reach the internet. There's no upload step, no server copy, and no way for us (or anyone else) to see what you're working on.
Are my files uploaded to a server?: No. There's no server-side processing here. The whole tool is a tiny app that runs in your browser — we don't even have a server that could receive your files. You can confirm this by opening your browser's network tab while you use the tool: nothing leaves your device.
Do I need to sign up or pay?: No. There's no account, no email collection, no credit card. The tool is free to use as much as you want, on as many files as you want. We're supported by a few unobtrusive ads on the page — not by your data.
Is this a word-level or line-level diff?: Line-level using LCS. For word-level diff inside changed lines, use a dedicated tool — that's on the roadmap.
Will huge files work?: Diff is O(n*m) so multi-megabyte files get slow. For source code, you're fine.