Paste a list and keep only the first occurrence of each line. The original order survives, so a deduplicated export still reads the way you built it.
There are two ways to remove duplicates and they give different answers. Sorting the list and collapsing neighbours is fast, but it destroys the order you built. This tool keeps the first occurrence of each line exactly where it appeared and drops every later copy, so a priority-ordered list stays in priority order and an export still matches the sequence its source produced. That matters more often than it sounds: a deduplicated keyword list where the most important term has drifted to position forty is worse than one with a few repeats.
Two lines that look identical often are not. One may carry a trailing space from a copy-paste, another may differ only in capitalisation. Both toggles are on by default because that matches what people mean by duplicate: trim the ends before comparing, and fold case so Apple and apple collapse together. Turn case folding off when the distinction is real, variable names, case-sensitive IDs, or a list where Polish and polish are genuinely different words. Blank lines are dropped by default rather than treated as duplicates of each other, which keeps the output tight.
Yes. Each line stays at the position of its first appearance. Nothing is sorted, so a ranked or chronological list survives the pass intact.
By default yes, because that is usually what people mean. Switch off "ignore case" when the difference is meaningful, as it is for IDs and code identifiers.
They are removed by default. Turn on "keep blank lines" if the spacing is part of the structure you are preserving, such as a stanza break.