Remove Duplicate Lines Online - Free Duplicate Line Remover
The Delimiter.site Dedupe Lines tool removes duplicate lines from any list in real time. Paste your text, and the tool immediately separates unique lines into one panel and removed duplicates into another - so you can see exactly what was removed and copy each result independently.
It works on anything you can put one-per-line: email lists, SKUs, IDs, URLs, log entries or keyword lists. To remove duplicate lines from a comma-separated or tab-separated string, split it into lines with the delimiter converter first, dedupe it here, then join it back into the format you started with.
How Deduplication Works
Each line in your input is compared against every line seen before it. The first occurrence of any line is kept in the Unique Lines output. Every subsequent occurrence of the same line is moved to the Removed Duplicates output. The original order of unique lines is preserved. If you also need the list sorted, run it through the line sorter afterwards.
Case-Insensitive Mode
When Case-insensitive is enabled, lines are compared without regard to capitalisation. Apple, apple, and APPLE are treated as the same line, and only the first occurrence is kept. This is essential when deduplicating data collected from different sources where casing may be inconsistent.
Trim Lines
When Trim lines is enabled (it is on by default), leading and trailing whitespace is stripped from each line before comparison. A line with a trailing space is treated the same as the identical line without it - which is almost always the correct behaviour for real-world data.
| Setting | Apple vs apple | fig vs fig |
|---|---|---|
| Default | Both kept — different text | Both kept — trailing space differs |
| Case-insensitive on | One kept | Both kept |
| Trim lines on | Both kept | One kept |
| Both on | One kept | One kept |
Getting unique values without Excel
Excel has Remove Duplicates under the Data tab and a UNIQUE() function in
newer versions, but both need the data already in a sheet and neither shows you what was taken
out. Pasting here gives you the unique values and the removed rows side by
side, which matters when you are about to delete records.
The Two Output Panels
Unique Lines
The top-right panel shows every line that appeared exactly once, or the first occurrence of any line that appeared multiple times. This is your clean, deduplicated list.
Removed Duplicates
The bottom-right panel shows every line that was removed - the second, third, and subsequent occurrences of any duplicated value. This panel is highlighted in red so it is immediately obvious which lines were discarded. You can copy the removed lines separately to audit what was stripped.
How to Use the Dedupe Lines Tool
Step 1 - Paste Your List
Click Paste to pull text from your clipboard, or type directly into the input panel. The deduplication runs automatically on every change - there is no convert button to press.
Step 2 - Set Your Options
Toggle Case-insensitive and Trim lines in the control bar at the top. The output panels update immediately when you change either option.
Step 3 - Copy Your Results
Click the copy icon in the Unique Lines panel header to copy your clean list. Click the copy icon in the Removed Duplicates panel to copy the discarded lines for auditing. The item count in the bottom bar shows how many duplicates were removed.
Before you dedupe, check these
- Is it one item per line? A single comma-separated string is one line to this tool. Split it with the delimiter converter first.
- Turn on Trim. Trailing spaces are the number one reason identical-looking lines survive.
- Decide about case. For emails and usernames you almost always want case-insensitive on.
- Count before and after. The line counter tells you how many rows you actually dropped.
Common Use Cases
Cleaning Email and Contact Lists
Marketing lists collected from multiple sources often contain duplicate email addresses. Paste the combined list, enable Case-insensitive, and copy the unique lines to get a clean list ready for your email platform.
Deduplicating SQL Query Results
When a query returns rows without a DISTINCT clause, you may get duplicates.
Copy the result column, paste it here, and deduplicate faster than rewriting the query.
Preparing Import Files
CRMs, e-commerce platforms, and databases reject imports with duplicate primary keys. Deduplicate your CSV or list before importing to avoid validation errors and failed uploads.
Auditing What Was Removed
Unlike most dedupe tools that silently discard duplicates, the removed-duplicates panel shows you exactly what was stripped. Copy it to a separate document if you need a record of every duplicate that was found.
Where duplicates come from
- Merged exports — two CRM pulls with an overlapping date range.
- Form submissions — someone double-clicked submit.
- Copy-paste drift — the same block pasted twice into a find and replace job.
- Case differences — Sales@ and sales@ reach the same inbox.
- Joined tables — a SQL join without
DISTINCTmultiplies rows.
Once the list is unique, sort it and count what is left. The list clean-up guide explains why that order matters.
Worked Example
Input: Unique lines: Removed:
anna@mail.com anna@mail.com anna@mail.com
ben@mail.com ben@mail.com Ben@mail.com (case-insensitive)
anna@mail.com cara@mail.com
Ben@mail.com
cara@mail.com
With case-insensitive matching on, Ben@mail.com is recognised as a duplicate
of ben@mail.com — exactly what you want for email lists, where the two
deliver to the same inbox.
Frequently Asked Questions
Which copy of a duplicate is kept?
The first occurrence stays; later repeats are removed. Combined with order preservation, this means your list comes back identical except that repeats have vanished.
Does it remove duplicate words inside a line?
No. The Delimiter.site duplicate line remover compares whole lines. To dedupe repeated words within text, use the text tool, which has a dedicated remove-duplicate-words operation.
Why should I enable the trim option?
Lists copied from spreadsheets often carry invisible trailing spaces, making "apple " and "apple" look distinct to an exact comparison. Trimming strips that whitespace first so they match.
Can I see what was removed?
Yes — the second output panel lists every removed duplicate, so you can verify nothing legitimate was lost before using the cleaned list. Most dedupe tools skip this step.
How large a list can it handle?
Deduplication runs in your browser, so tens of thousands of lines process instantly and nothing is uploaded anywhere.