Are my customers' phone numbers and emails uploaded to a server when I paste them to remove duplicates?

Why the question deserves a pause

A list of phone numbers and emails is your customers' personal data, given to you so they could buy from you, not so it could travel to a third party. Many online text tools process text on their server, and some never say what happens to it afterwards. Before pasting a customer list into any website, find out where it is processed.

What exactly happens when you paste the list

• The list stays in the text box on the page you have open.
• Lines are compared by code running in the browser itself, and the result updates as you type or change options without any request to a server.
• The 'Copy result' button puts it on your device's clipboard, and the download button creates unique-lines.txt directly on your device.
• No sign-in, no saved history of previous lists, no share link.

Because all the work is local, speed depends on your device: the tool was tested on 100,000 lines and computed the result in under a second, although the text box itself takes several seconds to display a paste that large.

A careful way to clean a customer list

1. Export the list from your store or messaging tool as a single column: the number or the email. Leave names and addresses out if you do not need them.
2. Open the Duplicate-line remover, paste the column, and set the options that suit the data.
3. Copy or download the result and import it into your sending tool.
4. Press Clear to empty the box, and close the tab on a shared computer.

What is still your responsibility

• The clipboard: after copying, the list stays there until you copy something else, and some phone keyboards keep a clipboard history.
• The downloaded file: it stays in your Downloads folder until you delete or move it.
• A shared computer: the box holds the text as long as the page is open.
• Consent: cleaning a list does not mean you may message everyone on it. That depends on how you collected the data and what your customers agreed to.

Why we keep these tools in the browser

Most of the text work a seller needs, such as removing repeats, sorting and cleaning, does not need a server at all. The browser can do it quickly, and keeping the data on your device removes the 'where did my list go?' question. The removal itself is plain: the first occurrence of each line stays as written and in its place, later copies go, and no number or address is edited.