Free Remove Duplicate Lines Tool Online

Remove Duplicates cleans duplicate lines from any text. You paste a list, and the tool keeps the first occurrence of each line while removing all subsequent duplicates. It's the digital equivalent of going through a list and crossing out repeats. This is surprisingly useful: a list of email addresses from a conference sign-up might have the same person registered twice, or a log file might have repeated entries from a noisy service.

The deduplicator reads all lines into an array and builds a Set. In case-sensitive mode, each line is added to the Set as-is; in case-insensitive mode, a lowercase version is used as the key while the original case is preserved from the first occurrence. The Set guarantees uniqueness, and the insertion order is preserved by iterating through the original array and keeping only lines whose key is not yet in the seen set.