How the sort compares lines
The text is split on line breaks, blank and whitespace-only lines are discarded, and the rest are sorted with a locale-aware comparison in your browser language. Two settings on that comparison shape the result, and both are worth knowing.
The comparison ignores case and accents. Apple, apple, and APPLE are treated as identical for ordering purposes, and resume and résumé sort together rather than resume coming first because of where the accented character sits in the character table. That is almost always what people want from an alphabetical list, and it is not what a naive sort gives you.
Numbers inside the text are compared as numbers. That means item2, item10, item20 sorts in that order rather than item10, item2, item20. It is the same behavior a file manager uses, and it is the reason version strings and numbered items come out sensibly.
- Paste one item per line
- The sorted list appears immediately
- Blank lines are dropped
- Press Copy result
Ascending only, and what to do about it
The sort runs A to Z and there is no descending option, no reverse toggle, and no button to flip it. To get Z to A, sort here and then paste the result into Reverse List, which flips the line order. The two steps together give you a descending sort in about five seconds.
There is also no shuffle, no sort by line length, no sort by the second word, and no sort by a column. This tool does one comparison in one direction.
Duplicates are kept. If the same item appears three times it appears three times in the output, sitting next to itself. Run the result through Remove Duplicate Lines if you want one of each, which is easier after the sort than before it since duplicates are now adjacent and easy to spot by eye.
The whitespace trap
Leading whitespace is preserved on every surviving line, and it is part of the comparison. A line that starts with two spaces sorts differently from the same line without them, which means an indented list can come out in an order that looks wrong.
If your list was copied out of a document or a code block and some lines carry indentation, strip the leading spaces before sorting. Otherwise the indented items cluster together at one end regardless of their actual text.
One more nuance: the comparison uses your browser language. Alphabetical order is not the same in every language, so the same list can sort slightly differently on a machine set to a different locale. It only shows up with accented characters and language-specific letters, but it is real.