Duplicate Line Remover

This tool walks through your text line by line, keeps a record of every line it has already seen, and drops any line that repeats — while leaving the first occurrence of each line exactly where it was. That order-preserving behavior matters: a plain "sort and dedupe" approach would scramble the original sequence, which is fine for an alphabetized list but wrong for something like a chronological log or a list where position carries meaning.

The case-sensitive toggle controls whether "Apple" and "apple" count as the same line or two different ones. With it on, capitalization has to match exactly for two lines to be treated as duplicates; with it off, they're compared after lowercasing, so lines that differ only in case collapse into one. Whitespace at the start or end of a line is still significant either way — a trailing space makes a line technically different from its otherwise-identical twin.

Typical uses include cleaning up merged email or URL lists before an import, deduplicating log lines pulled from multiple sources, and tidying a word list or CSV column that accumulated repeats from copy-pasting.

The tool keeps a set of lines seen so far and drops any later repeat. This preserves the original order, unlike a sort-and-dedupe approach, which is why it suits email lists, log lines and ordered data.

Lines are compared exactly, so Apple and apple are different, and so are lines that differ by a trailing space. Clean up whitespace and casing first if you want those treated as duplicates.