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DevUtil

List Deduplicator - Remove Duplicate Lines Online

Deduplicated List

About the List Deduplicator

Duplicate entries creep into lists more often than you would expect. Exported CSV columns, email recipient lists, inventory SKUs, log files, DNS records gathered from multiple sources — any time data passes through several hands or systems, duplicates accumulate. Cleaning them manually is tedious and error-prone, especially once a list grows past a few hundred lines. This tool strips duplicates in real time, right in your browser, so you can paste a messy list and immediately copy back a clean one.

Common Use Cases

Marketing teams regularly need to deduplicate mailing lists before an email campaign to avoid sending the same message twice. Developers use it to clean up dependency lists, environment variables, or configuration entries that have been merged from multiple branches. Data analysts paste columns from spreadsheets to quickly see how many unique values exist in a dataset. System administrators use it to consolidate host lists, IP allowlists, or user account exports. The tool is format-agnostic: if your data is one item per line, it works.

How It Works

The deduplication runs entirely on the client side. As you type or paste text into the input field, the component splits the text by newline, optionally trims whitespace from each line, and walks through the list keeping track of values it has already seen. When a duplicate is encountered, it is silently dropped. The result is displayed in the output area alongside a summary showing how many items were in the original list, how many are unique, and how many duplicates were removed.

Options and Configuration

Three toggles let you tailor the behaviour. Case-sensitive mode (on by default) treats uppercase and lowercase as distinct, so "Server" and "server" are both kept. Turn it off when casing is inconsistent and you only care about the underlying value. Trim whitespace removes leading and trailing spaces from each line before comparison, which catches duplicates that differ only by invisible characters. Preserve original order keeps items in the sequence they first appeared; disable it to sort the output alphabetically for easier scanning. All three settings take effect instantly with no need to re-submit.

Frequently Asked Questions

What does the List Deduplicator do?
It takes a list of items (one per line) and removes every duplicate entry, leaving you with only unique values. The processing happens in real time as you type or paste, so there is no submit button to click.
How does case sensitivity affect deduplication?
When case-sensitive mode is on (the default), 'Apple' and 'apple' are treated as two different items and both are kept. Turn it off to treat them as the same entry, in which case the first occurrence is preserved and later duplicates are discarded.
Can it handle large lists?
Yes. Because the tool runs entirely in your browser using JavaScript, it can process lists with tens of thousands of lines without any network latency. Performance depends on your device, but modern browsers handle very large inputs comfortably.
How does the sorting option work?
By default, 'Preserve original order' is enabled, which keeps unique items in the same sequence they first appeared. If you turn this option off, the output is sorted alphabetically instead, making it easy to scan through the results.
Is my data private?
Completely. The entire deduplication process runs in your browser. No data is sent to any server, stored in any database, or shared with any third party. Close the tab and the data is gone.