What this tool does
Lists collect duplicates the way drawers collect spare batteries: merge two spreadsheets, paste sign-ups from three sources, combine this month's orders with last month's, and the same line quietly appears two or three times. Removing the extras by hand means scanning hundreds of lines and hoping your eyes catch every repeat. Paste the list here instead, press one button, and the tool compares every line against the ones before it: the first occurrence of each line is kept, in its original position, and every later identical copy is removed. The line underneath the button tells you exactly what happened — how many lines went in, how many duplicates were removed, and how many lines came out — so you can sanity-check the result before you copy it.
Typical candidates: email and mailing lists, keyword lists, product SKUs, inventory counts, guest lists, survey responses, song playlists, lines of code or configuration, and the output of the Word Counter's cousin tasks — anything where one line should appear exactly once.
How a duplicate is decided
The comparison is exact, and that is deliberate. Two lines count as duplicates only if they are identical character for character. That means three things worth knowing:
- Capitalization matters. "Smith" and "smith" are different lines. If your list mixes cases, run it through the Case Converter first (lowercase everything) and then deduplicate.
- Spaces matter. A line ending in a trailing space is not the same as the same line without one, and neither is a line with two spaces where another has one. If a result surprises you — a duplicate you expected to vanish did not — invisible spaces are the usual culprit.
- Blank lines collapse. A run of empty lines is a set of identical lines, so only the first blank line is kept.
Exact matching is the safe default for a tool like this: it will never merge two lines you meant to keep separate, and the rules above tell you how to normalize a list first when you do want near-duplicates treated as one.
Order is preserved — on purpose
Many deduplication tools also sort the result alphabetically. This one does not: your list comes back in the order you put it in, minus the repeats. That matters more often than people expect — a ranked list, a running order, a set of instructions or a playlist all mean something by their sequence, and a cleaned list that has also been silently reshuffled is a new problem wearing a solved costume. If you do want the result sorted, sort it after copying it back into your spreadsheet, where you can see and control the sort keys.
Frequently asked questions
Does it matter that one line is capitalized differently?
Yes — matching is exact, so 'Apple' and 'apple' are kept as separate lines. To merge those, convert the whole list to lowercase with the Case Converter first, then remove duplicates.
Will my list be reordered or sorted?
No. The first occurrence of each line stays exactly where it was, and the surviving lines keep their original order. Only the repeat copies are removed.
What happens to blank lines?
Repeated blank lines are duplicates of each other, so only the first blank line is kept. A double-spaced list becomes single-spaced at each repeated gap.
How big a list can I paste?
Far bigger than anything you would edit by hand — the work happens in your browser, and lists of tens of thousands of lines process in well under a second on an ordinary computer.
Private by design: this tool runs entirely in your browser. The lists you paste here are never uploaded, stored or shared — safe for email lists and customer names.