Diff Checker
Compare two texts side by side.
Runs entirely in your browser. Nothing you enter or upload leaves your device.
What the diff checker does
When two versions of a file look almost the same, spotting what changed by eye is slow and unreliable. The diff checker lines the two texts up, works out which lines were added, removed or edited, and shows the result in two columns with line numbers, much like the review screen in a version control system.
People use it to check a config file before deploying it, compare a contract or policy against last year’s version, review code copied from a chat or email, or find the one row that differs between two CSV exports. It works with any plain text, so there’s no need to install anything or set up a repository first.
How to use the diff checker
- Paste the original on the left and the changed version on the right.
- Press Compare. Changed lines are paired, and the words that changed inside them are highlighted. The result also updates as you edit either side.
- Use the options to ignore whitespace or case. Long unchanged stretches are folded so the changes stand out.
Reading the results
The counters above the comparison give the number of lines added, removed, changed and unchanged. A removed line appears only on the left with a gap opposite it, and an added line appears only on the right. When lines are removed and added in the same place, they’re paired up as changed lines. Inside each pair, the exact words and symbols that differ are marked, so a single changed digit in a long line is easy to see.
Runs of unchanged lines are folded into a single “unchanged lines” marker, with three lines of context kept either side of each change. If the only differences are indentation, extra spaces or capital letters, tick the matching option and the tool will tell you the texts are identical with those settings. That’s a quick way to confirm a reformatted file still says the same thing. Swap sides flips which version counts as the original.
Questions
How does it decide what changed?
It uses the Myers diff algorithm, the same approach as git, to find the smallest set of line additions and removals that turns one text into the other.
Can I compare code?
Yes. Any plain text works, including code, configuration files and CSV.
Is there a size limit?
There’s no fixed size limit, but texts that need more than 2,500 line additions and removals are too slow to compare in a browser. The tool tells you if that happens. Compare in smaller sections.
Is my text uploaded?
No. The comparison runs in your browser.
Should I use this or the text compare tool?
Use this one for code, lists and anything where lines matter. For paragraphs of prose, the text compare tool marks changes word by word in one combined view.