Diff Checker

Diff Checker compares two versions of any text and shows what changed between them. Paste the original on the left and the new version on the right, or drop in two text files, and the differences appear straight away: removed lines marked with a minus, added lines with a plus, and edited lines shown side by side with the changed words highlighted inside them.

It is useful for checking what an editor changed in your article, spotting the one edited clause in a contract, comparing two configuration files, or reviewing code without a Git client. Long stretches of identical text fold away so you can focus on the changes, and the arrow buttons jump from one change to the next.

The comparison uses the Myers difference algorithm, the same method behind Git and the classic diff command, so it finds the smallest set of changes rather than guessing. It runs in a background worker inside your browser, which keeps the page smooth with texts of many thousands of lines. Nothing you paste is uploaded or saved.

1. Paste the older version into “Original text” and the newer one into “Changed text”. You can also press “Open” or drop a file on either box.
2. Read the summary above the result: lines added, removed and changed.
3. Choose “Side by side” or “Unified”, and highlight changes by “Words” or “Characters”.
4. Tick “Ignore whitespace” or “Ignore case” if spacing or capitals don’t matter to you.
5. Use the ↑ and ↓ buttons (or the N and P keys) to step through each change.
6. Press “Copy patch” or “Download .diff” to save the changes as a standard unified diff.

• Line-by-line comparison with the Myers algorithm, finding the smallest set of changes.
• Word-level or character-level highlights inside each changed line.
• Edited lines are matched to their closest counterpart, so a moved or reworded line isn’t mistaken for something else.
• Side-by-side and unified views, with line numbers for both versions and + / − markers, so changes never rely on colour alone.
• Ignore whitespace and ignore case options.
• Long unchanged stretches fold away, with one tap to show them or a switch to show everything.
• Previous and next change buttons with a “Change 3 of 12” position, plus keyboard shortcuts.
• Copy or download the result as a unified diff (patch) that git apply and patch understand.
• Swap the two sides, paste, clear with undo, and open or drop text files up to 50 MB.

• If almost every line shows as changed, the files may use different line endings or indentation. Tick “Ignore whitespace” to see the real edits.
• Character highlights are best for short lines such as codes, names and numbers. For prose, word highlights are easier to read.
• A patch made with “Ignore whitespace” or “Ignore case” switched on leaves out the differences you told it to ignore, so turn both off before saving a patch you plan to apply.
• One line break at the very end of a text is not counted as an extra empty line, because most files end with one.
• For Word documents or PDFs, copy the text out first and paste it in. The checker compares plain text, not formatting.