Diff Checker

Two versions of the same text rarely look different at a glance. A rental agreement comes back from the landlord with one clause quietly reworded, a client returns a quotation with a changed rate, a teacher wants to see what a student changed between drafts, or a developer needs to know why two config files behave differently. Reading both side by side line by line is slow and easy to get wrong. A diff checker does that reading for you and points at every change, however small.

The comparison works the way programmers' tools do. Each line of the original is matched with the changed text using Myers' difference algorithm, the method behind GNU diff and Git, which finds the smallest set of added and removed lines that turns one text into the other. We checked the results against git diff --minimal on real files and the counts match. Lines that were edited rather than replaced are paired up, and inside them the changed words are struck through on the old line and shown in solid black on the new line. Switch to Characters to catch a single changed digit in a PAN, an account number or an amount.

Large files are handled without freezing the page. The comparison runs in a background worker, long files are first lined up at lines that appear only once on each side, and a progress line appears if the work takes more than a moment. On a laptop two files of 120,000 lines with 300 scattered edits compare in well under a second. Files too long to show in a text box are kept as a file card and still compared in full, up to 64 MB a side. Long unchanged stretches fold into a Show unchanged lines button, so the changes stay in view.

Hindi and other Indian scripts are compared properly. Words are split on letters and vowel signs together, and character mode uses whole user-perceived characters as defined by Unicode, so a changed matra or halant is marked with its letter instead of being cut in half. The result uses signs as well as shades, a minus for a removed line and a plus for an added line, so it reads clearly in black and white, on a phone and for people who do not see colours well.

Your text stays on your device. The comparison runs inside this tab, and there are no share links that would store your text on a server. Contracts, salary sheets, exam answers and private code can be compared without sending them anywhere. Closing the tab clears everything.

When an option such as Ignore case or Ignore extra spaces is on, the downloaded .diff is meant for reading. Turn the options off to make a patch that patch tools can apply exactly. Word and PDF files are not read directly: copy their text and paste it here.