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Remove Duplicate Lines
Remove duplicate lines from a list — keeping the first of each and the original order — instantly in your browser. It shows the before and after line counts.
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Quick Answer
Paste a list and the tool removes duplicate lines, keeping the first occurrence of each and leaving the rest in their original order. It compares lines by their trimmed text, so lines that differ only in surrounding spaces count as the same, and it is case-sensitive. It also shows how many lines went in and came out. Everything runs in your browser; nothing is uploaded.
What the Remove Duplicate Lines Does
This tool takes a block of lines and gives you back just the unique ones. The first time a line appears it is kept; any later identical lines are dropped, and the surviving lines stay in the order you had them.
It is the quick way to clean up a list — email addresses, URLs, names, log lines — where the same entry has crept in more than once, without sorting or otherwise rearranging your data.
How It Works
The tool reads your text line by line and remembers each line it has seen. When it meets a line it has already kept, it skips it; otherwise it keeps it. To decide whether two lines are the same, it compares their trimmed content, so leading and trailing spaces do not stop a match.
Because it walks through the lines in order and keeps the first of each, the result preserves your original ordering rather than sorting it. It also reports the line count before and after, so you can see how many duplicates were removed.
Processing pipeline
- Read line by line. Split the text into lines and process them in order.
- Compare trimmed content. Match each line by its content with surrounding spaces ignored.
- Keep the first, drop repeats. Keep a line the first time it appears and skip any later identical lines.
- Show the counts. Report how many lines went in and how many remain.
How it de-duplicates
for each line, compare its trimmed text to the lines already kept
first time seen → keep it
seen before → drop it (order of the kept lines is preserved)Worked example
apple / banana / apple / cherry → apple / banana / cherry (4 lines in, 3 out)It keeps the first occurrence and preserves order. Matching ignores surrounding spaces but is case-sensitive, so Apple and apple are treated as different lines.
Standards & references
- First-occurrence de-duplication — Each unique line is kept the first time it appears and later repeats are removed, so the earliest version of a duplicated line survives.
- Order preserved — Lines stay in their original sequence rather than being sorted, so the de-duplicated list reads in the same order you pasted it.
- Trimmed, case-sensitive matching — Two lines match if their content is the same after trimming surrounding spaces. The comparison is case-sensitive, so different capitalisation counts as different lines.
Accuracy & Limitations
For a straightforward list, the result is exact: every unique line is kept once, in order, and every later duplicate is removed. The in and out counts confirm how many repeats went.
Matching is case-sensitive, so the same word in different cases — Apple and apple — is treated as two different lines and both are kept. Lower-case the text first if you want case to be ignored.
Lines are compared by their trimmed content, so two lines that differ only in leading or trailing spaces count as duplicates. The first one's original spacing is what stays in the output.
It removes whole-line duplicates only. It does not find duplicate words within a line, near-duplicates, or lines that differ by punctuation — those are kept as distinct. For those, a different cleanup step is needed.
Real-World Use Cases
Cleaning a list
Remove repeated emails, URLs or names from a list.
De-duplicating log lines
Collapse repeated log entries to unique ones.
Tidying pasted data
Drop duplicate rows pasted from several sources.
Preparing import data
Ensure a list of values has no repeats before importing.
When to use it — and when not to
Good for
- Removing repeated lines from a list
- Keeping the first of each, in order
- De-duplicating emails, URLs or names
- A quick clean without sorting
Not the best choice for
- Case-insensitive de-duplication (lower-case first)
- Finding duplicate words within a line
- Near-duplicate or fuzzy matching
- Sorting the list at the same time
To ignore case, convert the text to lower case first, then de-duplicate. To also sort, run the result through a line sorter. For near-duplicates, a fuzzy-matching tool is needed; this removes exact whole-line repeats.
Frequently Asked Questions
Which duplicate does it keep?
The first occurrence. The earliest time a line appears it is kept, and any later identical lines are removed, so the original first version survives.
Does it sort the lines?
No. It preserves your original order, simply dropping the repeats. If you also want the list sorted, run the de-duplicated result through a line sorter afterward.
Is the matching case-sensitive?
Yes. Apple and apple are treated as different lines, so both are kept. To ignore case, lower-case the text first, then remove duplicates.
Do leading or trailing spaces affect matching?
No. Lines are compared by their trimmed content, so two lines that differ only in surrounding spaces count as the same. The first line's original spacing is kept in the output.
Does it remove duplicate words within a line?
No. It works on whole lines, removing repeated lines. Duplicate words inside a single line are left alone, since the line as a whole is unique.
What do the in and out counts show?
How many lines you pasted and how many remain after de-duplication. The difference is the number of duplicate lines that were removed.
Are blank lines de-duplicated too?
Yes. A blank line trims to nothing, so multiple blank lines count as duplicates and only the first is kept. Bear that in mind if blank lines are meaningful in your data.
Can it handle a very long list?
Yes, it works on large lists efficiently, remembering each unique line as it goes. The de-duplication is fast even for thousands of lines.
Will it change the lines themselves?
No. It only removes duplicate lines; the kept lines are unchanged, with their original text and spacing. It does not edit the content of any line.
How is this different from removing all but unique lines?
Some tools remove every line that has a duplicate, leaving only lines that appeared exactly once. This tool keeps one copy of each line instead, which is usually what de-duplication means.
Is my data uploaded?
No. The de-duplication runs entirely in your browser. Nothing is sent to a server, so your list stays on your device.
Can I de-duplicate comma-separated values?
It works on lines, so put each value on its own line first. For values separated by commas on one line, split them onto separate lines, de-duplicate, then rejoin if needed.
References
Keeps the first occurrence of each line and drops later repeats, comparing lines by their trimmed content; preserves the original order and is case-sensitive.
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