About Line Deduper

Remove duplicate lines, preserve order or sort. Part of the DevTools Surf developer suite. Browse more tools in the Text / String collection.

Use Cases

• Removing duplicate entries from CSV data before import
• Cleaning up repeated error messages in application log files
• Deduplicating email lists before sending a newsletter campaign
• Removing redundant lines from hosts files or blocklists

Tips

• Choose between preserving original order or sorting the output
• See the count of duplicate lines removed in the summary
• Use this to clean up log files with repeated entries

Fun Facts

• The Unix 'uniq' command, which removes adjacent duplicate lines, was part of Version 3 Unix (1973) — but it requires input to be sorted first, unlike this tool.
• In data processing, deduplication can reduce storage requirements by 40-60% for typical log files and datasets with repeated entries.
• The concept of deduplication became critical in data centers around 2005, when NetApp and Data Domain popularized inline dedup for backup storage.

FAQ

Does order matter?

Two modes: preserve order (keep the first occurrence of each line, drop later duplicates) or sort + dedupe (sort then remove duplicates). Preserve is more common; sort is faster on huge files.

Is deduplication case-sensitive?

Yes by default. Toggle 'case-insensitive' for inputs where `FOO` and `foo` should be considered equal — useful for hostname lists and email dumps.

What about trailing whitespace?

Toggle 'trim before compare' so lines that differ only in trailing spaces are treated as equal. The output preserves the first occurrence's whitespace.

How large a file can it handle?

Streaming in theory, but browser memory caps practical size around 50MB. For multi-GB log files use `sort -u` or `awk '!seen[$0]++'` at the command line.