Use the free Remove Duplicate Lines below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
Where Duplicate Lines Come From
Duplicate lines sneak into lists constantly. You merge two mailing lists and half the addresses appear twice. You export data from two systems and the same IDs show up in both. You copy notes from several documents and repeat a paragraph without noticing. You scrape a page and the same link appears in the header, the body, and the footer. The list still works, but it is longer than it should be, counts are wrong, and anyone reading it wastes time on repeats.
This tool removes those repeats in one click. Paste the list, choose how strict the comparison should be, and get back the unique lines in their original order. The first copy of each line is kept, later copies are dropped, and a small summary tells you how many lines went in, how many unique lines came out, and how many were removed.
The Options, Explained
The case option decides whether Apple and apple count as the same line. Turn it on for lists where capitalization is inconsistent, such as tags or names typed by different people. Leave it off for lists where case matters, such as passwords, codes, or identifiers, where Apple and apple are genuinely different values. When case is ignored, the kept copy is the first one as you typed it, so the original capitalization survives.
The trim option removes spaces at the start and end of each line before comparing. This matters because invisible trailing spaces are a classic cause of false uniqueness: two lines that look identical are treated as different because one ends with a space. Trimming also cleans the output, since the kept lines lose their stray spaces. The empty-line option decides whether blank lines are kept or dropped. Lists pasted from documents often contain blank lines between sections, and dropping them gives a tighter result.
The sort option alphabetizes the result after deduplication. Sorting is useful when the original order does not matter and you want a tidy list for comparison, but it destroys meaningful order, such as a ranked list or a chronological log. Leave sorting off unless you specifically want an alphabetical list.
What Counts as a Duplicate
Comparison is exact, line by line. A line is a duplicate only if it matches a previous line completely, after applying your chosen options. A line that differs by one character, a comma, or a trailing period is not a duplicate, and the tool correctly keeps it. This exactness is a strength for data cleaning, but it means near-duplicates still need a human eye: “New York” and “New York ” are duplicates after trimming, but “New York” and “New York City” are different entries that no line tool should merge.
Line endings deserve a note. Files from Windows use a different line ending than files from Mac or Linux, and pasting between systems can leave invisible carriage return characters at the end of lines. If a list that looks clean still shows unexpected duplicates, invisible characters are the likely cause, and retyping or re-pasting the list usually clears them.
Practical Uses Beyond Mailing Lists
Developers use line deduplication on lists of URLs, error messages, and log lines, where the unique set is far more informative than the raw flood. Writers use it on keyword lists and outlines, where repeats signal a section that needs merging. Teachers use it on collected answers and survey responses, where counting unique responses matters more than counting submissions. Anyone who has ever sorted a spreadsheet by hand to find repeats will recognize the time saved.
For very large lists, the browser handles tens of thousands of lines comfortably, because the algorithm uses a set for lookups rather than comparing every line against every other line. A list of a hundred thousand lines may still feel slow in a browser tab, and for that scale a command-line tool is the better choice: sort -u on Unix sorts and deduplicates a file in one step, though it sorts where this tool preserves order.
Frequently Asked Questions
Does it keep the first or the last copy? The first copy, in its original position, so your list order is preserved.
Why do two identical-looking lines both survive? Check for invisible differences: trailing spaces, different capitalization, or a hidden character. Turn on trimming and case-insensitive matching to catch the first two.
Can it remove duplicate words inside a line? No. This tool works line by line. For words inside a line, split the text into one word per line first, deduplicate, and rejoin.
Paste the list, press the button, and work with the unique lines instead of the repeats.
Related Tools
Also available in Spanish: Eliminar LÃneas Duplicadas Online Gratis – Borra LÃneas Repetidas al Instante.
More free tools: cURL Command Builder – Build cURL Commands Free Online, API Request Code Generator – Generate Fetch and Python Snippets Free, Open Graph Card Preview – Preview Social Share Cards Free Online, URL Query Parameter Editor – Edit URL Query Parameters Free Online, MIME Type Lookup – Find the MIME Type of Any File Extension Free, JSON Key Sorter – Sort JSON Keys Alphabetically Free Online, SSH Config Generator – Generate SSH Config Files Free Online, Nginx Config Generator – Generate Nginx Server Blocks Free Online, Env File Generator – Generate .env Files Free Online.