Remove Duplicate Lines from Text — Free Online Deduplicator

Q: Why are two visually identical lines not treated as duplicates?

Almost always trailing or leading whitespace. A line ending in a space or tab is a different string from one without it, so a raw comparison keeps both. That is why "Trim whitespace before comparing" is on by default — it strips that whitespace before testing for equality, collapsing the visually identical lines into one.

Q: What happens to empty and blank lines?

By default empty lines are kept and the first blank line counts as the unique blank, so later blanks are removed as duplicates. Turn on "Remove empty lines" to strip every blank and whitespace-only line first, before deduping, so they never appear in the output or inflate the duplicate count.

Q: Can I sort the result alphabetically?

Yes. Toggle "Sort result A to Z" and the unique lines are sorted alphabetically after deduping. The sort honors your case setting: case-insensitive ordering when case-sensitive match is off, exact Unicode code-point ordering when it is on.

Q: How many lines can it handle?

Deduping uses a JavaScript Set, which gives O(n) average-time lookups, so it handles hundreds of thousands of lines comfortably in a modern browser. For typical lists up to ~50,000 lines the result appears in well under 100 ms as you type.

Paste a list and remove duplicate lines instantly, keeping the first occurrence of each. Trim whitespace before comparing, ignore case, drop empty lines, and optionally sort A→Z — with a live count of how many duplicates were removed. 100% client-side.

Case-sensitive matchTrim whitespace before comparingRemove empty linesSort result A→Z

Input · 7 lines

Samples:

Output · 4 unique(3 duplicates removed)

alice@example.com
bob@example.com
carol@example.com
dave@example.com

Input lines: 7Unique kept: 4Duplicates removed: 3

Keep First Occurrence

Each line survives only its first time. Later duplicates are dropped, so the original order of the unique lines stays intact unless you choose to sort.

Trim Before Comparing

On by default. Leading and trailing spaces, tabs, and CRLF endings are stripped before comparison, so "apple" and "apple " collapse into one entry instead of two.

Case-Insensitive by Default

Apple and apple are treated as the same line out of the box. Flip on case-sensitive matching when capitalization is meaningful, like passwords or codes.

Drop Empty Lines

Optionally remove blank and whitespace-only lines first, so they never inflate the duplicate count. Useful for tidying CSV columns and scraped data.

Optional A→Z Sort

Sort the deduplicated result alphabetically in one click. Sorting runs after deduping and honors your case-sensitivity setting for the ordering.

100% Client-Side

Everything runs in your browser. Lists may hold emails, customer IDs, or internal data — they never leave the page, and the tool works offline once loaded.

Remove duplicate lines from a list online

Remove Duplicate Lines takes a list of lines and deletes every repeated entry, keeping the first occurrence of each. Paste one item per line, and the unique lines appear instantly with a count of how many duplicates were removed. By default it trims whitespace before comparing and ignores case, so visually identical lines collapse correctly. Toggle case-sensitive matching, empty-line removal, or an A–Z sort. It runs 100% in your browser, free, with no upload.

How to remove duplicate lines

Paste or type your list into the input pane, one entry per line, or load a sample.
Leave Trim whitespace before comparing on so lines that differ only by spaces or tabs still merge.
Turn on Case-sensitive match only if capitalization should keep two lines separate (codes, passwords).
Optionally enable Remove empty lines to drop blanks, and Sort result A→Z to alphabetize the survivors.
Read the live counts (input lines, unique kept, duplicates removed), then press Copy.

How deduping works: a Set of comparison keys

The tool splits your text on newlines, then walks the lines top to bottom. For each line it builds a comparison key — the line after optional trimming and optional lowercasing — and checks that key against a JavaScript Set. If the key is new, the line is kept and the key remembered; if the key was seen before, the line is a duplicate and dropped. A Set gives average constant-time lookups, so the whole pass is roughly O(n) in the number of lines.

Two settings change the key, not the kept text. Trim whitespace runs String.prototype.trim on each line before comparison, so "apple" and "apple " share a key. Case-sensitive match, when off, lowercases the key so Apple and apple share one. Because keys are compared and original (trimmed) lines are kept, the output stays clean while the comparison stays forgiving.

Worked examples: input → output

Default settings · keep first

apple, banana, apple, cherry, banana → apple, banana, cherry

The first apple and first banana are kept in place; later copies are dropped. Output reports "2 duplicates removed".

Case-insensitive (default)

Apple, apple, APPLE → Apple

All three share the lowercased key "apple", so only the first (Apple) survives. Turn on case-sensitive match to keep all three.

Dedupe + Sort A→Z

cherry, apple, cherry, banana → apple, banana, cherry

Duplicates collapse first, then the unique survivors are sorted alphabetically.

Edge case · trailing whitespace

"apple" and "apple " (one with a trailing space) look identical but are different strings. With Trim whitespace off they both survive — a phantom duplicate. With it on (the default), they collapse to one. This is the single most common reason a "deduped" list still has visible repeats.

When removing duplicate lines saves real time

Use Case	Why Deduping Helps
Cleaning import lists	Strip repeated email addresses, customer IDs, or SKUs before a bulk CRM, spreadsheet, or database import so each record loads once.
Deduping tag clouds	Collapse a pasted column of keywords, tags, or categories down to the unique set before counting or building a taxonomy.
Merging two lists	Paste two lists end-to-end, dedupe, and you have their union — every entry that appears in either list, listed once.
Sanitizing scraped data	Screen-scraped or CSV-exported rows often carry trailing spaces; trim-before-compare removes phantom duplicates a plain dedupe would miss.
Building allow/deny lists	Produce a clean, unique, optionally A→Z list of domains, IPs, or usernames for a firewall, spam filter, or config file.
Tidying CSV columns	Copy one column out of a spreadsheet, drop empties, dedupe, and sort to get the distinct values that column actually contains.

Deduper Behaviors & Practical Tips

Trim-before-compare is on by default

It strips leading and trailing whitespace before comparing, so "apple" and "apple " collapse into one. Turn it off only when spacing is meaningful.

Case-sensitive matching is off by default

With it off, "Apple" and "apple" are treated as the same line. Turn it on to keep different capitalizations as distinct entries.

First occurrence always wins

The earliest copy of each line is kept and later copies are dropped, so the original order of the surviving lines is preserved unless you sort.

Drop empty lines runs before deduping

Blank and whitespace-only lines are removed first, so they never count as a "duplicate" of each other in the totals.

Sort A→Z reorders only the survivors

Deduping happens first; the optional alphabetical sort then arranges the unique lines, using case-insensitive order when case-sensitive is off.

Option reference

Four independent options control how lines are compared and presented. This table maps each option to what it changes and the default state.

Option	What it does	Default
Case-sensitive match	Treats `Apple` and `apple` as different lines	Off
Trim whitespace before comparing	Strips leading/trailing spaces, tabs, CR before the equality test	On
Remove empty lines	Drops blank and whitespace-only lines first, before deduping	Off
Sort result A–Z	Alphabetizes the unique survivors after deduping	Off

The invisible-character trap most dedupers ignore

Trailing whitespace is the famous culprit, but it is not the only invisible difference. A line copied from the web can carry a non-breaking space (U+00A0) where you expect a normal space, or a stray zero-width space (U+200B) that renders as nothing at all. String.prototype.trim removes standard whitespace including U+00A0, so this tool's trim option does fold a leading or trailing non-breaking space — but a zero-width space sitting inside a line, or a non-breaking space in the middle, will keep two lines distinct. If a dedupe leaves what look like exact duplicates, paste the two lines into our Find & Replace tool and strip the odd character first.

One honest limit worth stating: the optional A–Z sort compares by raw Unicode code points (lowercased when case-insensitive), the same model JavaScript's built-in sort uses. It is not locale-aware collation, so it will not place Swedish ä after z the way a language-specific sort would. For most lists of words, emails, and IDs that distinction never matters.

Runs 100% in your browser

Your lists never leave your device. Every dedupe, trim, and sort runs locally in JavaScript — no upload, no XHR, no analytics event carries your line content, and copying uses the native clipboard. That matters because these lists often hold customer emails, internal IDs, or other sensitive identifiers. I tested it on the bundled samples (an email list with a trailing-space duplicate, tags with blank lines, customer IDs, mixed-case names) with every option toggled, and on a 50,000-line list where deduping still completes in well under 100 ms. Verify it yourself in DevTools → Network: no request fires while you dedupe.

Frequently asked questions

Is this duplicate line remover free?

Yes. It is 100% free with no signup and no usage limit. Every feature — deduping, trimming, case matching, and sorting — is available to everyone.

Does it run in my browser?

Yes. All processing happens in JavaScript inside your browser tab. Nothing is uploaded to a server, so the tool also works offline once the page has loaded and your list never leaves your device.

Which copy of a duplicate line is kept?

The first occurrence. As the tool scans top to bottom, it keeps the earliest copy of each line and drops every later copy, so the original order of the survivors is preserved unless you turn on the A–Z sort.

Why are two visually identical lines not treated as duplicates?

Almost always leading or trailing whitespace. A line ending in a space or tab is a different string from one without it, so a raw comparison keeps both. That is why "Trim whitespace before comparing" is on by default — it strips that whitespace before testing for equality.

Is the matching case-sensitive?

No, not by default. "Apple" and "apple" are treated as the same line and collapsed to one. Turn on "Case-sensitive match" when capitalization matters — for example with codes or passwords — and the two are kept as distinct lines.

What happens to empty and blank lines?

By default the first blank line is the unique blank and later blanks drop as duplicates. Turn on "Remove empty lines" to strip every blank and whitespace-only line first, so they never appear in the output or inflate the duplicate count.

Can I sort the result alphabetically?

Yes. Toggle "Sort result A–Z" and the unique lines are sorted alphabetically after deduping. The sort honors your case setting: case-insensitive ordering when case-sensitive match is off, exact code-point ordering when it is on.

How many lines can it handle?

Deduping uses a JavaScript Set with O(n) average-time lookups, so it handles hundreds of thousands of lines comfortably. For typical lists up to ~50,000 lines the result appears in well under 100 ms as you type.

Is my data sent anywhere?

No. There is no fetch, no upload, and no analytics event that carries your line content. Lists often hold customer emails or internal IDs, so they stay on your device. Verify in DevTools, Network tab: no request fires while you dedupe.