Remove Duplicate Lines

Removes duplicate lines from a block of text. The first occurrence of each line is kept and every subsequent duplicate is dropped, so original ordering is preserved. Comparison is exact and case-sensitive — "Apple" and "apple" are treated as different lines.

Useful for cleaning up word lists, log files, exported CSVs, scraped output, anywhere you have a chance of repeated content. Runs entirely in your browser — your text never leaves the page.

When you reach for this

Cleaning email lists

Pasted email exports often contain duplicates from form-fill mistakes or merge artefacts. Remove duplicates before importing into a CRM or sending a campaign.

Deduplicating word lists

Compiling a vocabulary list, brand-name brainstorm, or keyword set? This tool gives you a clean unique list in one paste.

Filtering log files

Identical log lines from a noisy service can drown out the real signal. Strip duplicates to see the unique events.

Cleaning CSV columns

Paste a single CSV column and get back the unique values. Faster than opening a spreadsheet for a one-off task.

Code-review output review

Linter or compiler output sometimes repeats the same warning across builds. Dedupe to focus on the unique problems.

What gets processed (and how)

The tool splits input text into lines using the newline character (\n). It normalizes line endings from CRLF (\r\n) to LF to ensure consistent splitting across platforms. Each line is then processed sequentially: an internal hash set records the exact content of each line (case‑sensitive, whitespace‑sensitive). If a line is not yet in the set, it is appended to the output and added to the set; if it is already present, it is skipped. The order of first occurrences is strictly preserved. The final output is reassembled by joining the kept lines with newline characters, and a trailing newline is added only if the original input ended with one (to match typical editor behavior).

How to use it

1. Paste or type your text into the input box.
2. Click the Remove Duplicates button.
3. The deduplicated text appears instantly in the output area.
4. Copy the result to your clipboard with one click.

Behavior on tricky inputs

Trailing newline

A trailing newline is preserved in the output only if the original input ends with one, so no accidental blank line is added.

Empty lines

Empty lines are treated as distinct lines; multiple consecutive empty lines become a single empty line if they are duplicates.

Whitespace-only lines

Lines containing only spaces or tabs are considered different from truly empty lines and are deduplicated on exact content.

Case sensitivity

'Apple' and 'apple' are treated as different lines because comparison is exact and case‑sensitive.

Workflow tips

• Trim trailing whitespace before deduplication if you want to treat 'apple ' and 'apple' as identical.
• Use the case‑sensitive nature to keep distinct capitalization variants intentionally.
• For large datasets, paste in chunks; the tool runs entirely in the browser without server limits.
• Combine with the Sort Lines tool to first sort then deduplicate for a different result.

vs other ways to do this

Compared to common alternatives, this tool preserves original ordering and requires no command‑line knowledge.

Where this came from

Removing duplicate lines is a fundamental text processing task that originated in early Unix tools. The classic uniq command (V7 Unix, 1979) could only remove consecutive duplicates, requiring a prior sort. Later, sort -u combined sorting and deduplication. The need to preserve original order led to awk scripts like awk '!seen[$0]++', a pattern that became idiomatic. This tool implements that same logic client‑side for instant, no‑install use.