Paste two versions of a text and see exactly what changed: lines marked with + were added, lines marked with - were removed, and everything else stayed the same.
Line by line, using a longest-common-subsequence comparison. Unchanged lines are prefixed with two spaces, lines only in A with "- " and lines only in B with "+ ". The counts shown are added, removed and unchanged lines.
Yes — each side is capped at 2000 lines. Larger input is truncated and a warning is shown, because the comparison grows with the size of both sides.
No. The comparison runs 100% in your browser and nothing is uploaded — both versions stay on your device.