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Remove Duplicate Lines

Remove Duplicate Lines — a fast, free text utility that runs entirely in your browser.

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About the Remove Duplicate Lines

A Remove Duplicate Lines tool identifies and removes repeated text lines from a block of input while preserving the order of first occurrence. The tool parses any multiline text—separated by Windows (CRLF), Unix (LF), or old Mac (CR) line endings—and filters each line against all previous lines, keeping only the first instance of each unique string. This is useful for cleaning up datasets, CSV/JSON records, log files, configuration lists and any text that should contain only distinct entries.

How Remove Duplicate Lines works

How Remove Duplicate Lines Works

  1. Paste or type your text into the input box (multiline text with duplicates).
  2. The tool splits the text on any line separator (Windows CRLF, Unix LF, or old Mac CR).
  3. It compares each line against all previous lines using exact string matching (case-sensitive).
  4. The first occurrence of each unique line is kept; any identical lines that appear later are removed.
  5. The result is joined back into text with Unix line breaks and displayed instantly.

Worked Example

Input:

apple
banana
apple
cherry
banana
date

Output:

apple
banana
cherry
date

What happened: The second "apple" (line 3) was removed because "apple" already appeared on line 1. The second "banana" (line 5) was removed because "banana" already appeared on line 2. Lines that appeared only once ("cherry" and "date") were kept unchanged. The output preserves the order of first appearance.

How to use

  1. Type or paste your text into the input box.
  2. The result updates instantly as you type.
  3. Click Copy to use the output.

Common uses

  • Cleaning up CSV or spreadsheet exports with duplicate rows (e.g., merged datasets from multiple sources).
  • Removing duplicate log entries to focus on unique events and errors in application logs.
  • Deduplicating DNS nameserver lists, email address lists, or other system configuration data before importing.
  • Filtering supplier or customer lists to identify distinct entries for mailing and outreach campaigns.
  • Removing repeated user IDs or item SKUs from e-commerce order exports before processing.
  • Testing form validation and database constraints that should prevent duplicate submissions.

Frequently asked questions

What if two lines are the same except for capitalization (e.g., 'Apple' and 'apple')?
The tool treats them as different lines and keeps both, because the matching is case-sensitive. If you need to ignore case, copy the output and convert it to a consistent case first.
Does this tool work with files?
No, but you can open a text or CSV file in a text editor, copy the contents, paste them into the tool, and copy the cleaned result back.
Will the blank lines be removed?
No. Blank lines are preserved as separate entries unless they are exact duplicates. A blank line followed by another blank line will become a single blank line.
What happens to the line breaks? Will my output match my input?
The tool converts all line endings (Windows CRLF, Unix LF, Mac CR) to Unix LF (\n). If your file used Windows line breaks, the output will use Unix line breaks. Most text editors and tools handle both transparently.
Is my data uploaded to a server?
No. The entire operation runs in your browser using JavaScript. Your text never leaves your computer and nothing is logged.
Can I remove all instances of a duplicate (not just keep the first)?
This tool keeps the first occurrence and removes later ones. If you need to remove all instances of duplicated lines, you would need a different tool or manually edit the results.