About

Online Diff Checker is the free tool at onlinediffchecker.com. Paste two texts — or load them from this device — and click Check diff. Additions, deletions, and edits are marked in the two boxes. The comparison runs in this tab.

Most “online diff” pages either look abandoned or they ship your text to a server so they can meter a plan. This site is the other option: a static page, a small script, and a worker on your device. There is no account. There is no comparison API.

What we built it for

The comparisons that never belonged in someone else’s logs: environment files, customer exports, a clause you are not ready to put in email, two versions of a config from machines you should not copy off of. Text, JSON, XML, YAML, lists, images, PDFs, and Word documents each have a tool. All of them still run in this tab.

How it works

The algorithm is Myers’ shortest edit script, via the diff package, in a Web Worker so a large paste does not freeze the tab. A first pass is line-oriented. Changed lines get a second pass at word grain. Optional history and your color scheme live in this browser’s localStorage. Closing the tab drops the editors unless you saved history.

What it is not

• Not a layout redline. PDF Diff and Word Diff extract wording; they do not keep fonts, tracked changes, or pixel-perfect pages. There is no spreadsheet tool.
• Not a three-way merge. Use git merge-file or a desktop tool when you have a common ancestor.
• Not a syntax-aware compiler. JSON Diff can ignore key order; YAML Diff can compare as data. The text tool still treats those files as characters.
• Not a cloud product. We do not store the paste, and we cannot restore it for you.

Who operates the site

The site is operated as Online Diff Checker at onlinediffchecker.com. Contact. Privacy. Terms.