How Remove Duplicate Lines works
Remove Duplicate Lines keeps the first occurrence of each line and drops every later repeat. Comparisons are exact by default, but can be made case-insensitive ("Apple" = "apple") or trim-aware (leading and trailing whitespace ignored). Output order matches the order of first appearance in the input — useful for log analysis, list cleanups, and id whitelists.
How to use
Paste a list and toggle the strictness options that match your data. The output updates live and shows you only the unique entries. Combine with Sort Lines to get alphabetised deduplication.
Frequently asked questions
Does Remove Duplicates preserve the order of first occurrence?
Yes. The tool walks the input once and remembers the first index where each distinct line was seen. Output is in that original order, so context is not lost.
Is "Apple" the same as "apple" by default?
No. By default the comparison is case-sensitive and byte-exact. Enable "Case insensitive" to treat them as duplicates, or "Trim whitespace" if extra spaces are causing false duplicates.
Can I keep only the duplicates instead of removing them?
Yes — pipe your input through this tool, then subtract the unique result from the original using a diff tool or shell command, or invert the workflow by sorting and counting.
Are empty lines treated as duplicates of each other?
Yes. An empty line equals an empty line, so multiple blank lines collapse to a single blank line. Use Sort Lines or Remove Extra Spaces afterwards if you want to drop blanks entirely.
How big can my input be?
The tool keeps a Set of seen lines in memory, so the limit is roughly how much your browser can allocate — typically several hundred thousand lines on a modern machine.