Duplicate Line Remover

Yes. The first occurrence of each line is kept in its original position, and subsequent duplicate occurrences are removed. The relative order of unique lines is preserved.

Case-sensitive mode treats "Apple", "apple", and "APPLE" as different lines. Case-insensitive mode treats them as the same line, keeping the first occurrence as-is and removing the rest regardless of case.

By default, leading/trailing spaces are not ignored — ' apple' and 'apple' are treated as different lines. Enable the 'ignore leading/trailing whitespace' option to normalize whitespace before comparison, so those lines would be considered duplicates. This is useful for cleaning up copy-pasted data with inconsistent spacing.

The tool shows a count of duplicates removed but doesn't list them individually. To see what was removed, run the tool, then use a Diff Checker to compare the original text with the deduplicated result. Each removed duplicate will appear as a deletion, letting you verify the results.

The deduplicator uses a Set (for case-sensitive) or Map (for case-insensitive) internally, giving O(n) time complexity. It handles tens of thousands of lines smoothly in the browser. For files with millions of lines, consider splitting the data or using a command-line tool like sort -u or awk for better performance.

The deduplication and sorting are separate operations. Use this tool first to remove duplicates, then copy the result to our Line Sorter tool to sort the remaining unique lines.