How to remove duplicate characters
Removing duplicate characters means two different things, and mixing them up gives the wrong answer. One is collapsing a run such as aaa into a single a. The other is dropping every character that has already appeared, keeping only its first occurrence. Because the results differ so much, the mode is the first thing you choose here, and collapsing consecutive repeats is the default.
You can also decide whether case matters and whether whitespace takes part. With case sensitivity off, A and a count as the same character and the form that appeared first is the one that stays. Whitespace is excluded by default, since including it would leave a single space in the entire text and ruin the wording. When whitespace is skipped, or when case is ignored, the result panel says so explicitly.
Characters are split into graphemes, the units a reader perceives as one character, so emoji and combining marks stay whole instead of being cut apart. The panel shows the original count, the remaining count and exactly how many characters were removed, which makes it easy to confirm that the cleanup did what you intended.
Frequently asked questions
Take aabca. Collapsing consecutive repeats gives abca, while keeping only first occurrences gives abc. The first is for stretched-out text, the second for listing which characters were used.
Yes. The text is split into graphemes, the units a reader sees as single characters, so a combined emoji such as a family sequence is treated as one item and never cut in half.
Including them would leave a single space in the whole text and destroy the wording. The default keeps whitespace untouched, and the checkbox lets you include it when you really want to.