Diff two things.
Paste the before and after. See what changed by line, word or character, side by side or as a unified patch. JSON mode sorts keys first so reordered objects do not show up as changes. Nothing leaves your browser.
Result
About this tool
The two inputs are split into lines, words or characters and compared with a longest common subsequence algorithm, the same idea behind diff and git diff. Lines only in the original are shown as removed, lines only in the new version as added, and the side by side view lines up changed blocks so you can read across. Unified view produces the familiar - and + layout and the Copy patch button gives you that as text.
Ignore whitespace collapses runs of spaces and tabs and trims line ends, which hides reformatting and indentation changes. Ignore case does what it says. JSON mode parses both sides, sorts every object's keys recursively and pretty-prints them before comparing, so two API responses that differ only in key order come out identical, and a real change in a nested value shows up on exactly one line.
Useful for: comparing config files between environments, checking what a formatter or minifier changed, reviewing a JSON payload against the version you expected, spotting the one character that differs between two tokens, and producing a patch to paste into a ticket. Everything runs in your browser; the text is never sent anywhere. Line mode handles a few thousand lines per side comfortably.