Remove Duplicate Lines Online

Removing duplicate lines is one of the most common text-cleaning tasks for developers, data analysts, and content creators. Whether you are deduplicating a list of email addresses, cleaning up exported CSV data, removing repeated log entries, or simply tidying up a word list, this tool does the job instantly in your browser without any server interaction.

The deduplication algorithm uses a hash set that tracks seen lines in a single pass over the input, making it run in linear O(n) time and efficiently handle even very large text files. The Case Sensitive toggle lets you choose whether 'APPLE', 'Apple', and 'apple' should be considered the same line. The Trim Whitespace option normalises lines before comparison so that ' apple ' and 'apple' are treated as duplicates — a common need when working with pasted spreadsheet data. The original order of lines is always preserved, and the first occurrence of each unique line is kept in place.

This tool processes everything locally in your browser. Your text is never uploaded to any server, making it safe to use with sensitive or confidential data. There is no line limit — the tool handles thousands of lines without any delay.

You may also find our Sort Lines, Whitespace Remover, and Word Counter helpful.