Paste two JSON documents to see the differences line by line with syntax highlighting, then switch to the Data tab for a structural comparison. The Data view lists each change by its path, such as items[id=3].price, and ignores key order, so reformatted or reordered JSON only shows real changes.
Lists of objects are matched by an id, key, uuid or name field when every item has one, so an item that moved within an array isn't reported as changed.
Not in the Data view: two objects with the same keys and values are equal whatever order the keys are in. In the text view, use Tools, Format JSON and sort keys to normalise both sides first.
If every item in both arrays is an object with a unique id, key, _id, uuid, code or name field, items are matched by that field. Otherwise they are compared by position.
Not to compare it. The comparison runs entirely in your browser. Text and files are not uploaded. There are no ads, accounts or analytics. History is off by default. You can opt in to local history or manually save comparisons in your browser; do not save sensitive secrets.