Remove Duplicate Rows from a CSV File

The first one. Rows are kept in their original order, and any later row that matches a row already seen is removed. If you want to keep the most recent record instead, sort the file newest-first before removing duplicates.

Choose these columns match and tick only the column that identifies a record, such as email or customer_id. Two rows then count as duplicates when that column matches, even if other columns differ. Tick several columns to match on a combination, such as first name + last name + date of birth.

Only if you ask for it. Tick Ignore upper and lower case and Ignore spaces at the start and end of values to treat them as duplicates. The row that is kept is written exactly as it was in the file.

Yes. Tick Also save the removed rows to a separate file. You then get a second CSV with the header and every removed row, which is a good way to check the result before deleting anything.

To handle files larger than your computer's memory, the tool remembers a 64-bit fingerprint of each row instead of the row itself. Two different rows would have to produce the same fingerprint to be confused, and the odds of that are about 1 in 3.7 billion for a file with 100,000 unique rows, and about 1 in 370,000 for 10 million unique rows. For any file that fits in Excel, you can treat the result as exact.

Yes, that is the point of this tool. Duplicates are found by code running in your own browser and the cleaned file is written to your own disk, so a list of real names and email addresses never leaves the machine it is already on. No account, no server-side copy, and nothing retained after you close the tab.