What this does
Paste one version of your text on the left and the other on the right. The two are lined up side by side with line numbers: removed lines are red on the left, added lines are green on the right. When a line was only edited rather than replaced, the exact words that changed are highlighted inside it. Long stretches of identical text fold away so you only read the parts that changed.
What you can compare
Anything made of text: source code in any language, JSON, YAML, CSV exports, SQL scripts, log files, translations, contracts, essay drafts, or two versions of an email. It works in any language and any script, not only English. You can also drag a text file straight onto either box instead of pasting.
Is my text private?
Yes. The comparison is done by JavaScript running on your own device. Your text is never uploaded, never stored and never logged. That matters when you are comparing a contract, a config file with passwords in it, or a list of customer names.
What the options do
Ignore case treats "Hello" and "hello" as the same. Ignore whitespace ignores extra spaces and indentation, which is useful for reformatted code but should stay off for YAML, where indentation carries meaning. Swap flips the two sides, and Copy diff puts the result on your clipboard in the standard - and + format that developers expect.