Remove Duplicate Lines
Free duplicate-line remover. Strip repeated lines from any list, log, or text dump. Optional case-insensitive matching and original-order preservation.
Quick answer
Read each line, hash it (or normalize for case-insensitive), and keep only the first occurrence. Optional: sort the result, ignore whitespace, or strip empty lines. The tool runs in-browser so even multi-megabyte logs process instantly.
Remove Duplicate Lines
How it works
Splits the input on line breaks, walks through each line in order, and keeps only the first occurrence of each unique value. Optional trimming removes leading and trailing whitespace before comparing; case-insensitive mode treats "Apple" and "apple" as the same.
When to use it
Deduping email lists, contact lists, URLs, log files, CSV columns, or any other line-based data. The output preserves the original order of first occurrences.
Common mistakes
Forgetting that whitespace counts. " apple" and "apple " look identical but aren't unless you check the trim option. Leading whitespace from copy-paste indentation is a common gotcha.
How duplicate removal works
The tool walks through your input line by line, keeping a set of lines it has already seen. If a line is already in the set, it's skipped; otherwise it's added to both the set and the output. The result preserves the original order of first occurrences. For case-insensitive comparison, lines are normalized to lowercase before being checked. Whitespace-trimmed comparison strips leading/trailing spaces before matching, which is useful for files with inconsistent indentation or trailing whitespace.
When to use it
Cleaning up email lists or contact CSVs to remove duplicates before bulk operations. Deduplicating log files for grep'ing or analysis. Combining multiple lists (e.g. import and export sets) and stripping overlap. Generating a unique vocabulary list from a long text. Cleaning bibliographies or citation lists.
Common mistakes
- Treating spaces as significant when you don't mean to. 'foo' and 'foo ' (with trailing space) are different lines unless you trim. Toggle the trim option for most casual deduplication.
- Case-sensitive matching on emails or URLs. Email local parts are technically case-sensitive but virtually always treated case-insensitively in practice. Use case-insensitive mode for email and URL deduplication.
- Forgetting that empty lines count as duplicates. If your input has 50 blank lines between sections, the dedup output will have just one blank line. Sometimes that's what you want; sometimes it isn't.
Frequently asked questions
How do you remove duplicate lines from text?
Paste the text into the tool above. It walks through line by line, keeping only the first occurrence of each line. Order is preserved. Optional: case-insensitive matching, whitespace trimming, and sorting before/after dedup.
Does the tool work for case-insensitive matching?
Yes — toggle the case-insensitive option. 'Apple' and 'apple' will be treated as duplicates. The output preserves whichever case appeared first in the input.
Is there a line limit?
No fixed limit — the tool runs entirely in your browser, so memory is the only constraint. Even multi-megabyte input lists process in seconds on a modern device.