Frequently asked questions

dedup.ing is a free, browser-based tool that removes duplicate entries from any list. Paste plain text, upload a CSV, or drop in an Excel file, and the tool returns a clean, deduplicated result in seconds. No account or registration is required. All processing runs inside your browser, so nothing is sent to a server.

The tool also includes a family of adjacent text utilities: Sort Lines, Compare Two Lists, Trim Whitespace, Change Case, and Count Lines.

Yes. The core deduplicate tool is free with no account required. You can paste a list, configure matching options, run the deduplication, and copy or download the result without signing up for anything.

Yes. The tool is fully responsive and works on phones and tablets. You can paste a list from your clipboard, configure matching options, run the deduplication, and copy or download the result without needing a desktop browser.

All deduplication runs entirely inside your browser. Your list data never leaves your device. Nothing is transmitted to dedup.ing servers, logged, or stored.

No. The tool is free and requires no account or registration.

dedup.ing accepts plain text (paste directly or upload a .txt file), CSV (.csv), and Excel (.xlsx and .xls). File parsing runs entirely in the browser using SheetJS for Excel files and Papa Parse for CSV.

For CSV and Excel files, the advanced mode lets you choose which columns to deduplicate on and decide which row to keep when duplicates are found.

Yes. Upload your CSV file and switch to Advanced mode. The tool detects your column headers automatically. Select the columns to match on, set whether to keep the first or last duplicate row, and click Dedupe. All other columns in the surviving rows are preserved in the output.

You can copy results directly to your clipboard or download them in multiple formats, including plain text (.txt), comma-separated values (.csv), Excel spreadsheets (.xlsx), Markdown tables (.md), and PDF documents (.pdf).

Yes. Toggle case-insensitive matching in the options panel. With this setting on, Apple, apple, and APPLE are treated as the same value and collapsed into a single entry.

Yes. Enable trim whitespace in the options panel. This strips leading and trailing spaces before comparing rows, so   apple   and apple are treated as identical.

You choose. The options panel gives you two settings: keep first (the default) or keep last. When duplicates appear, the tool retains the occurrence you specify and removes the others.

The tool processes up to 500,000 rows in the browser. Inputs above 50,000 rows are handled in a background thread using Web Workers, so the page stays responsive throughout. You can expect results on a 50,000-row list in under 2 seconds and on a 500,000-row list in under 10 seconds on a modern device.

Most browser-based dedup tools run all processing on the main JavaScript thread. When a list gets large, this blocks the page and can cause it to freeze or crash. dedup.ing offloads heavy work to a Web Worker thread for any input over 50,000 rows. The main thread stays free, so the UI remains interactive while processing runs in the background.

Paste your email list into the text area, one address per line, then click Dedupe. Enable case-insensitive matching and trim whitespace to catch variants like User@Example.com and user@example.com.

If your emails are in a CSV column, upload the file in Advanced mode and select the email column as the match key.

In Google Sheets, go to File → Download → Comma-separated values (.csv). Then drag the downloaded file onto the dedup.ing tool. Switch to Advanced mode to pick the column to deduplicate on, choose first-or-last, and click Dedupe. Download the result as a CSV and re-import it into Sheets if needed.

Yes. Toggle sort output in the options panel to sort the result alphabetically before it is returned. For more sorting options, use the standalone Sort Lines tool.

dedup.ing includes a family of free text utilities, each on its own URL:

• Sort Lines: sort alphabetically, numerically, or by length.
• Compare Lists: diff two lists.
• Trim Whitespace: strip leading/trailing spaces.
• Case Convert: convert UPPER/lower/Title case.
• Count Lines: count lines, words, chars, bytes.

All tools work the same way: paste in, process, copy or download out. No account required.