FAQ
Does deduplication keep the original order?
Yes, the first occurrence of each line is kept in its original position. Use the sort tool if you want alphabetical order.
Can it ignore case?
Yes, with the option enabled ABC and abc count as the same line and the first one is kept.
Are blank lines removed?
Yes. Skip-blank-lines is enabled by default, so empty lines at the top and bottom disappear; clear the checkbox to keep them.
About this tool
The unit of comparison is the whole line: two lines are duplicates only when they are identical after trimming leading and trailing whitespace. There is no similarity matching, no ignoring of punctuation and no ignoring of word order — "apple banana" and "applebanana" are two different lines.
Both the comparison and the output use the trimmed line, which means leading indentation is removed. That is what you want for lists of names, tags or IDs, but it is wrong for indentation-sensitive content — pasting code, a Markdown list or YAML will lose the structure along with the spaces.
With "ignore case" enabled the comparison key is lowercased, but the output keeps the capitalisation of the first occurrence: Apple first yields Apple, apple first yields apple. Order also follows first appearance and is never re-alphabetised — sort afterwards with the line sorter if you want order by value.
Skip blank lines is on by default, so empty lines at the top and bottom of pasted text simply disappear. "Show count" prefixes each line with the occurrence count and two spaces, and from that point the output is no longer clean data (3 apple is a single line) — feeding it back in deduplicates the new lines instead. Copy counted output out rather than reusing it as input. The status bar reports total lines, kept lines and duplicates removed, which is how you check whether blank lines skewed the result.