Method 1: use a browser tool
Paste the list into a deduplication tool, click once and copy the result. This is the fastest route when you have a one-off job and do not want to install anything.
A browser tool is also the safest option for sensitive data, because the text never leaves your machine - nothing is uploaded to a server.
Method 2: spreadsheet
Paste the list into a single column in Excel, Google Sheets or LibreOffice, then use the Remove Duplicates command, or the UNIQUE() formula in Google Sheets and newer Excel.
This is the best option when the list is part of a larger table and you need to keep the other columns aligned with the cleaned rows.
Method 3: command line
On Linux or macOS: sort file.txt | uniq > clean.txt. The sort is required because uniq only removes adjacent duplicates.
To keep the original order instead: awk '!seen[$0]++' file.txt > clean.txt. That pattern is worth memorising - it handles huge files without loading everything into memory.
Method 4: SQL
If the data lives in a database, SELECT DISTINCT column FROM table returns unique values directly. Add ORDER BY if you need a stable sort.
For duplicates across multiple columns, use GROUP BY on all of them, or ROW_NUMBER() over a partition when you need to keep one specific row per group.