Guide

How to Remove Duplicate Lines From a List

Copy-pasted lists often contain repeats: the same email twice, a keyword added by two people, a product code listed again. Removing duplicates by hand is slow and error-prone. Here is how deduplication works.

How deduplication works

The tool reads your text one line at a time and remembers every line it has seen. The first time a line appears, it is kept; any later identical line is removed.

This means the original order is preserved — your list isn't re-sorted.

Worked example

apple, banana, apple, cherry, banana (one per line) becomes apple, banana, cherry. Two duplicate lines are removed, and the tool tells you the count.

Ignoring letter case

By default, "Apple" and "apple" count as different lines. Turn on Ignore letter case to treat them as the same; the first version that appears is the one kept.

This is useful for email addresses and keywords, where capitalization rarely matters.

Watch out for hidden spaces

"apple" and "apple " (with a trailing space) are different lines. If duplicates survive, clean the spacing first with the Whitespace Cleaner, then remove duplicates.

Common uses

Removing duplicates is handy for:

Mailing and contact lists
SEO keyword lists
Product codes or IDs from spreadsheets
Log lines and error messages

Try it yourself

Put this guide into practice with our free Remove Duplicate Lines — no sign-up, no download.

Open the Remove Duplicate Lines