Compare two lists, one item per line. See what is only on the left, only on the right, or in both.
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A list here is one item per line. The page splits each side, then reports the lines that appear only in A, only in B, and in both. Order follows the first time a line is seen.
Trim and Drop empty start on. Ignore case is off, so A and a are different. Ignore case uses the locale lowercasing of this page, and the displayed line keeps the spelling from the side it was taken from.
A: alpha, beta B: beta, gamma
Only in A: alpha Only in B: gamma In both: beta
A: beta, beta B: beta
In both shows beta once. The second copy is not a separate item.
Leave Trim off and wonder why id and id plus a space differ
Turn Trim on, or look at the space on the Invisible characters page
This is not a text diff. Line 1 of A is not compared with line 1 of B. A line matches wherever it sits in the other list.
Ignore case can merge strings that are different code points, such as a Latin capital and a small letter. The first spelling wins.
Line breaks from Windows and from old Mac files are split before the switches run. A line is then trimmed if that switch is on.
The share link stores both lists and the three switches, not the three results. Opening the link compares them again. Anyone who has the link can read both lists.
The three columns are the set difference A−B, the set difference B−A, and the intersection. Duplicates are removed after the key is chosen, so the result is a set even when the paste is not.
Old Mac OS used a single CR, U+000D, as a line break. Windows uses CR LF. The split covers both, plus a lone LF.