Duplicate Detector

How to use it

1. Paste your list into the input box. One item per line, any length, no formatting required.
2. Pick a mode. Unique list strips repeats and keeps the first spelling. Duplicates only shows what repeated. Frequency counts every line and sorts by count.
3. Turn on case insensitive matching if Foo and foo should count as the same entry, which is usually what you want for emails, tags and usernames.
4. Turn on trim whitespace if the list came out of a spreadsheet or a copied table, where trailing spaces are invisible but make two identical lines compare as different.
5. Read the summary line for the totals, then copy the result straight out of the output box.

What people use it for

Notes and limits

• Nothing is uploaded. Detection runs in your browser, so the list never leaves your machine and there is no request to inspect. That still means avoid pasting secrets you would not keep in your own browser history.
• Comparison is line based, not token based. A trailing comma or a different quote character makes two lines distinct, which is why trim whitespace matters on anything pasted out of a spreadsheet.
• Case insensitive matching keeps the first spelling it sees. If you paste USER@example.com before user@example.com, the unique list keeps the uppercase one.
• Very large lists are limited by browser memory rather than a hard cap. Lists in the hundreds of thousands of lines work but the browser tab does the work, so expect a pause on the biggest inputs.
• Order is preserved in Unique list mode. Frequency mode sorts by count, highest first, so the two modes answer different questions and are not interchangeable.