Remove duplicate lines
Keep only the first occurrence of each line.
Remove duplicate lines keeps just the first occurrence of each unique line in a block of text, removing any later repeats, with an option to control whether matching is case-sensitive.
How to use
- Paste your text.
- Toggle case-sensitivity if "Line" and "line" should count as the same or different.
Common use scenarios
- Deduplicating a list of email addresses or names before a mail merge.
- Cleaning up a log file that has repeated identical lines.
- Removing duplicate URLs from a list before processing them.
- Tidying up a list of tags or keywords that has accidental repeats.
✓Content & verification reviewed: 2026-08-25
How we verify Remove duplicate lines
How to confirm duplicates were detected and removed the way you expect.
Case-sensitivity toggle changes what counts as "duplicate"
With case-sensitivity on, "Apple" and "apple" are treated as different lines and both kept; with it off, they're treated as the same line and only the first occurrence survives — pick based on whether case differences matter for your data.
Line order is preserved
The result keeps lines in their original order — specifically, the position of each line's first occurrence — rather than sorting or grouping them, so the overall sequence of your list is unchanged aside from the removed repeats.
Exact-line matching, not fuzzy matching
Lines must match exactly (aside from the case-sensitivity setting) to be considered duplicates — a line with a trailing space or slightly different formatting won't be recognized as a duplicate of an otherwise-identical line.
Before you rely on the result
- You've decided whether case-sensitivity should be on or off for your data.
- You understand lines must match exactly (case aside) to be treated as duplicates — check for stray trailing spaces if expected duplicates aren't being caught.
- You've confirmed the result's line order still makes sense for your use case.
- You've pasted the complete list, not a partial excerpt that might miss duplicates across the boundary.
Who this is for
- Anyone deduplicating an email or contact list before a mail merge.
- Developers cleaning up log files with repeated lines.
- Anyone removing duplicate URLs or IDs from a list before further processing.
- People tidying up tag or keyword lists that ended up with accidental repeats.
Real-world examples
Deduplicating an email list before a mail merge
Someone combines contact lists from two sources and ends up with duplicate email addresses; removing duplicates ensures each person only receives one copy of a mail merge.
Cleaning a log file
A developer has a log file with the same repeated warning message on hundreds of lines; deduplicating makes it much easier to see the distinct set of issues that actually occurred.
Removing duplicate URLs before a crawl
Someone compiles a list of URLs from multiple sources and deduplicates it before feeding it into a script, avoiding redundant processing of the same page twice.
Limitations
- Line order is preserved — the first time each line appears is the one that's kept.
Frequently asked questions
Which occurrence of a duplicate line gets kept — the first or the last?
The first occurrence in the original order is kept; any later repeats of that same line are removed.
What's the difference with case-sensitivity on vs. off?
With it on, "Apple" and "apple" are treated as different lines and both are kept; with it off, they're treated as the same and only the first survives.
Why isn't a line I expected to be a duplicate being removed?
Lines must match exactly (aside from case, depending on your setting) — a trailing space, extra tab, or other small formatting difference will prevent two otherwise-identical-looking lines from being recognized as duplicates.
Does this sort or reorder my list?
No — the result preserves the original line order; only the later duplicate occurrences are removed, everything else stays in place.
🔒 Runs in your browser — nothing is uploaded. Results are for reference only; see the disclaimer. Last updated: 2026-08-25
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