Remove Duplicate Lines

What is the Remove Duplicate Lines tool?

The Remove Duplicate Lines tool takes any block of text, looks at it line by line, and gives it back with every repeated line stripped out — keeping just one copy of each, in the same order you typed it. It is the fast fix for messy lists: a column of email addresses with copies scattered through it, a dump of log lines, a keyword list pasted from three different places, or a set of CSV rows where the same record sneaked in twice. Instead of eyeballing thousands of rows or writing a one-off script, you paste, read how many were removed, and copy the clean result.

This is a different job from the sibling Remove Line Breaks tool. That tool joins short lines back into flowing paragraphs; this tool deduplicates lines, dropping the repeats. One reshapes wrapping, the other removes redundancy — they never overlap. And it all runs in your browser, so the lists you paste never leave your device.

How to use it

1. Paste or type your text into the input box, one item per line.
2. Toggle the options you need — case-insensitive, trim, keep first or last, drop blanks, or show only duplicates.
3. The cleaned text appears instantly with a stats line: lines in, unique, removed.
4. Click Copy result and close the tab. Paste, scan the count, copy, leave.

There is no button to press to run it — every change updates the output live.

The method behind it

The dedup is deterministic and runs entirely in your browser. The text is split into lines on every newline (Windows and Mac line endings are normalized first). For each line the tool builds a comparison key: if trim is on, leading and trailing whitespace is dropped from the key; if case-insensitive is on, the key is lowercased. Lines whose keys match are treated as the same line.

In keep first mode the tool walks top to bottom and writes a line the first time its key appears, ignoring every later copy. In keep last mode it walks the same way but, when a key repeats, the surviving copy is taken from the latest occurrence while holding the line's final position. Either way the order of your remaining lines is preserved — nothing is sorted or shuffled.

Options explained

• Case-insensitive matching — treats Apple and apple as the same line, so only one survives. Off by default, so capitalization differences count as distinct lines.
• Trim whitespace before comparing — ignores stray leading and trailing spaces or tabs, so a padded line and a clean one are recognized as the same (and the output is trimmed too).
• Keep first vs keep last — chooses which copy of a repeated line stays. The set of unique lines is identical; only the surviving copy's source position differs.
• Remove blank lines — drops empty lines from the result entirely, handy when your paste is peppered with gaps.
• Show only duplicates — flips the output to list just the lines that appeared more than once (one of each), so you can see exactly what was repeated.

Worked example

Take a six-line list: banana, Apple, banana, apple, a blank line, then orange. With case-insensitive on, trim on, and remove-blank on, the output is banana, Apple, orange — the second banana is gone, apple is folded into Apple, and the blank line is dropped. The stats line reads: 4 lines in, 3 unique, 1 removed. Flip to show-only-duplicates and you get just banana and Apple, the two lines that had repeats.

Common use cases

• Cleaning email or contact lists so each address appears once before an import.
• Deduplicating keyword and tag lists stitched together from several sources.
• Tidying log files to collapse repeated error lines into one of each.
• Prepping CSV or data rows where the same record was pasted twice.
• Auditing a list with show-only-duplicates to find exactly which entries repeat.

Why use this one, and how it pairs with the toolkit

Most duplicate-line removers are a single crude button with no matching options, so they miss Apple versus apple, choke on stray spaces, and never tell you how much they removed. This tool adds real controls — case-insensitive matching, trim-before-compare, keep first or last, drop blanks, and a show-only-duplicates view — plus a live stats line so you can trust the cleanup at a glance. It runs in your browser, asks for no account, and works instantly on mobile.

It also pairs cleanly with the rest of the kit. The Remove Line Breaks tool does the opposite job on the same text — merging wrapped lines into paragraphs. If your list also has runs of extra spaces or odd character widths, the Text Formatter tidies that spacing, and the Case Converter normalizes capitalization on the same pasted text.

Frequently asked questions