Remove Duplicate Lines Case Insensitive — Online Free Tool

What case-insensitive deduplication does

When case-insensitive mode is active, the tool lowercases each line internally before comparing it to previously seen lines. The original casing of the first occurrence is preserved in the output — only the comparison is case-insensitive.

The first occurrence of [email protected] is kept, and the two other capitalizations are removed as duplicates.

When you need case-insensitive mode

Case-sensitive deduplication (the default) is correct for data where capitalization carries meaning — file paths on Linux, programming language identifiers, passwords. For most content-level data, you want case-insensitive mode:

• Email addresses — the email protocol treats addresses as case-insensitive by convention. [email protected] and [email protected] reach the same inbox.
• Keyword lists — best running shoes and Best Running Shoes represent the same search intent.
• Domain names — Example.com and example.com are the same host.
• Product names entered manually by different people often have inconsistent capitalization.
• Tags and categories in CMS exports often have mixed casing depending on how they were created.
• City and country names from form inputs where users typed freely.

Combining with trim whitespace

Case differences and whitespace padding are often introduced by the same process — manual data entry or sloppy exports. Enable both "Case insensitive" and "Trim whitespace" together to catch all near-duplicates that differ only in formatting.

The combined effect: [email protected] and [email protected] are treated as the same line. The first occurrence (after trimming) is kept in the output.

Which occurrence is kept?

By default, the tool keeps the first occurrence. You can switch to keeping the last occurrence using the toggle in the tool. This matters when the casing of the first occurrence is not the canonical form you want.

Example: if your list has APPLE first (from an old export) and Apple second (from a newer, cleaner export), switch to "Keep last" to retain the properly cased version.

Frequently asked questions