Remove Duplicate Lines - Deduplicate Text Online

When to remove duplicate lines

Duplicate lines crop up constantly in real-world text work: log files with repeated entries, email address lists with duplicates from multiple exports, configuration files with copy-paste errors, or word lists merged from multiple sources. Cleaning them manually is tedious and error-prone; this tool does it instantly.

How duplicates are detected

Two lines are considered duplicates when their comparison keys match. The comparison key is determined by the options you choose:

• Case-sensitive (default on): "Hello" and "hello" are different lines. Turn this off to treat them as the same.
• Trim whitespace: with this on, " hello " and "hello" are the same line. The first occurrence is kept with its original spacing.

Order is preserved

The first occurrence of each unique line is kept. Later occurrences are removed. The output is in the same order as the original input. This is a stable deduplication.

Duplicate report

Expand the "Show duplicate lines" section to see exactly which lines appeared more than once and how many times each appeared. The list is sorted by frequency, so the most-repeated line appears first.

Advanced use cases

• CSV deduplication: paste the entire CSV including headers; the tool treats each row as a line. To deduplicate on a specific column rather than the whole row, sort the CSV by that column first so identical values cluster together.
• URL lists: paste a list of URLs to remove exact duplicates. Note that http:// and https:// versions of the same URL are treated as different values; normalize protocol before pasting if needed.
• Database exports: when exporting query results to a plain-text list for cleanup, paste here to quickly identify repeated IDs, emails, or codes before re-importing.

Keep first vs. keep last

By default this tool keeps the first occurrence of each duplicate and removes all subsequent ones — the standard behavior for most deduplication tasks. Some scenarios require keeping the last occurrence (e.g., a changelog where the most recent entry for a version should win). For keep-last behavior, reverse the list before pasting, run deduplication, then reverse the result.