Remove Duplicate Lines
Paste a list and instantly remove duplicate lines. Choose case-sensitive or insensitive matching, trim whitespace before comparing, and keep the first or last occurrence. Preview what changes before applying.
Input Text
Deduplication Options
Select how duplicates should be detected, review the highlighted preview, then click Apply.
Treat uppercase and lowercase as different values — "Apple" and "apple" are kept as distinct lines.
Strip leading and trailing spaces from each line before comparing — " hello " and "hello" count as the same.
When a duplicate is found, keep the last occurrence instead of the first.
Why Use This Tool?
Removing duplicate entries is one of the most common list-cleaning tasks — whether you are deduplicating email lists, cleaning up keyword sets, processing log files, or merging data from multiple sources. This tool applies a line-by-line deduplication algorithm entirely inside your browser. Your data never leaves your device.
Case-Insensitive Matching: Catch duplicates regardless of capitalisation. "ERROR", "error", and "Error" all count as the same entry when case-insensitive mode is active.
Whitespace Normalisation: Invisible leading or trailing spaces often cause duplicates to slip through automated checks. Enable Trim Whitespace to catch entries that differ only in surrounding spaces.
Undo Anything: Every apply action is tracked in history. Click undo to instantly restore the previous text if you changed your mind.
How to Use It
- 1
Paste your list into the text area above — one item per line. You can paste from a spreadsheet, a text file, or anywhere else.
- 2
Choose your options: toggle Case Sensitive if capitalisation matters, enable Trim Whitespace to ignore surrounding spaces, and switch to Keep Last Occurrence if you want the last version of each duplicate retained.
- 3
Review the Preview panel. The Before column highlights every line that will be removed in red; the After column shows the clean deduplicated list.
- 4
Click Apply to update the text area with the clean list, then Copy Result to send it to your clipboard.
Frequently Asked Questions
What algorithm does this tool use to remove duplicates?
The tool uses a single-pass Set-based deduplication algorithm. It iterates over each line once, building a normalised comparison key (after optional trimming and case folding), and uses a JavaScript Set to track which keys have already been seen. Lines whose key is already in the Set are marked as duplicates and excluded from the output. This runs in O(n) time relative to the number of lines.
Is my data safe when I use this tool?
Yes, completely. The remove duplicate lines tool runs 100% client-side in your browser using JavaScript. No text is ever sent to a server, stored in a database, or logged anywhere. It is safe to paste email lists, passwords, confidential documents, or any other sensitive data — none of it leaves your device.
What is the difference between Case Sensitive and Case Insensitive mode?
In case-insensitive mode (the default), the tool converts each line to lowercase before comparing, so "Apple", "APPLE", and "apple" are all treated as the same entry and only the first is kept. In case-sensitive mode, those three lines are considered distinct and all three are preserved. Use case-sensitive mode when you are working with data where capitalisation is meaningful — for example, programming identifiers or passwords.
Why would I want to Keep Last Occurrence instead of first?
In some workflows, the last occurrence of a value is the most up-to-date version. For example, if you have a log file where each line represents an event and duplicate IDs appear because an entry was updated, keeping the last line gives you the most recent state. The default (keep first) is better when you want to preserve the original order of first appearances.
What does the Trim Whitespace option do exactly?
When Trim Whitespace is enabled, the tool strips leading and trailing space characters from each line before comparing it to others. This means a line that reads " hello " (with surrounding spaces) is compared as "hello" and will match a line that reads "hello" exactly. The original line content — including its spaces — is preserved in the output; only the comparison key is trimmed, not the line itself.
Can I use this tool to deduplicate CSV or spreadsheet data?
Yes, but the tool operates on whole lines. If you paste one value per line (a single column from a spreadsheet), it works perfectly. For multi-column CSV data, each full row is compared as a unit — so two rows are only considered duplicates if every field matches. To deduplicate by a single column in multi-column data, extract that column first, deduplicate it here, then rejoin. Need to compare two versions of a list? Try our compare-text tool.
What happens to blank lines?
Blank lines are treated like any other line. If your input has multiple blank lines, all but the first (or last, depending on your setting) will be removed as duplicates. If you want to remove all blank lines entirely, use the Remove Spaces tool which has a dedicated Remove Empty Lines option. Combining both tools gives you a fully cleaned list.
Explore More Free Text Tools
Word Counter
Count words, sentences, readability score, and more in real time.
Find & Replace
Find and replace text with optional regex support.
Case Converter
Convert text to uppercase, lowercase, title case, and more.
Compare Text
Diff two text blocks and highlight every change.
Remove Spaces
Remove extra spaces, fix PDF line breaks, and clean up text.
Sort Lines
Sort lines A-Z, Z-A, by length, or shuffle randomly.