List Duplicate
Duplicate list items online with concatenate or interweave modes. Set custom copies, separators, and repeat lists instantly in your browser.
What does the List Duplicate tool do?
It takes a list of items and creates multiple copies of them. You can arrange copies by appending them after the original (concatenate) or alternating each item with its copies (interweave).
How do I duplicate a list online?
Paste or type your list items, choose a separator (comma, newline, space, semicolon, or tab), set the number of copies, pick a mode, and click Duplicate.
What is concatenate mode?
Concatenate mode appends all copies after the original list. For example, [A, B] with 3 copies becomes [A, B, A, B, A, B].
What is interweave mode?
Interweave mode groups each item with its copies. For example, [A, B] with 2 copies becomes [A, A, B, B].
What separators are supported?
You can split input by comma, newline, space, semicolon, or tab. Output can be joined with any of the same separators.
Is my data safe?
Yes. All processing happens locally in your browser. No data is sent to any server, and no registration is required.
Is this tool free to use?
Yes, the List Duplicate tool is completely free with no usage limits or hidden fees.
Can I duplicate a large list?
Yes. The tool runs entirely in your browser using JavaScript, so it handles large lists efficiently without uploading anything.
What are common use cases?
Use it to generate test data, create repeated patterns, build CSV rows, prepare bulk text entries, or multiply items for data processing tasks.
Does it work on mobile?
Yes. The tool is fully responsive and works on desktop, tablet, and mobile browsers.
What is the maximum number of copies?
You can set up to 100 copies per item, which is sufficient for most list duplication needs.
Can I customize the output separator?
Yes. You can choose a different separator for input splitting and output joining independently.
How to Use List Duplicate
List Duplicate repeats every item in your list a chosen number of times. Everything runs locally in your browser, so your data never leaves your device.
- Paste your items into the input box, for example apple,banana,cherry, separated by commas or another delimiter.
- Under "Split by:", select the delimiter your list uses: a comma, "Newline", "Space", semicolon, or "Tab".
- Set "Copies:" to how many times each item should repeat, then pick "Concatenate" or "Interweave" under "Mode:".
- Under "Join with:", choose the separator placed between items in the duplicated output.
- Tick "Trim whitespace" or "Remove empty" to clean up items before they are duplicated.
Concatenate repeats each item in blocks, while Interweave repeats the whole list round after round — pick the mode that matches the order you need.
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