Remove duplicate lines

Duplicate line remover

What the remove duplicate lines tool does

Paste a list with repeats scattered through it, and this app returns one copy of each line: the first time it shows up, kept; every later repeat, dropped. Your original order stays intact, so the tenth unique line going in is still the tenth line coming out.

It runs entirely in your browser. Paste, dedupe, copy: nothing you paste is uploaded, and there's no cap on how many lines you process or how often.

For anything resembling a real list, a subscriber export, a set of URLs, a batch of log lines, keeping that original order matters as much as removing the repeats does. This tool never touches the order of what survives.

Workflow

How to remove duplicate lines in three steps

No settings to configure.

Step 1

Paste your list, one item per line.

Step 2

Press Remove duplicates. It runs instantly, on your device.

Step 3

Copy the deduplicated list out.

How it decides

Order-preserving, not sorted

This tool walks the list top to bottom, keeps the first appearance of each line, and drops every repeat that comes after. Nothing gets reordered alphabetically or any other way; what comes out is in exactly the sequence the surviving lines were already in.

That's not a small detail if the order in your list carries meaning, a log in chronological order, a sequence of steps, a form where the earliest mention is the one that should stick. A tool that sorted before deduping would hand you a technically correct set of unique lines arranged in an order that no longer means anything.

What counts as identical

Duplicates are matched exactly, capitalization included

Two lines only count as duplicates when they're identical character for character. 'Apples' and 'apples' read as two separate lines to this tool, since the capital letter makes them unequal strings, even if you'd naturally call them the same item.

For case-insensitive deduplication, run the case converter first to bring everything to one consistent case, then dedupe the result. Convert first, then remove repeats: doing it in the other order won't catch anything the case difference was hiding.

The usual gotcha

Why a line that looks like a duplicate survives the pass

This is the number one reason a duplicate shows up in the output when it shouldn't have. 'apples' and 'apples ' with an invisible trailing space are identical on screen and different underneath, so an exact-match comparison treats them as two distinct lines.

The same thing happens with a trailing tab, or a stray carriage return left over from converting a file between Windows and Unix. If duplicates are surviving this tool, run the whitespace minifier or a hidden-character cleaner first to strip whatever's making visually identical lines different in the bytes. Once that pass is done, run the duplicate remover again on the result, since normalizing whitespace can itself turn two previously distinct lines into exact matches.

Why it matters

What duplicate lines cause in practice

A mailing list with a repeated address sends the same person the same message twice. A CSV import carrying duplicate rows inflates a count that's supposed to represent unique entries. A config file with a setting repeated on two lines can behave unpredictably depending purely on parse order.

In any automated pipeline reading a word list, a keyword list or a set of test cases, duplicates cost processing time at minimum and silently double-weight an entry at worst.

Who it's for

Who uses a duplicate line remover, and when

Marketing and data teams cleaning an email list or a customer export use it to get one entry per unique value before a campaign tool sees it. Developers dedupe log lines, file path lists and test case sets for exactly the same reason.

It also comes up merging two overlapping lists, combining subscriber exports from two sources and wanting exactly one copy of every address that appears in either or both.