Spreadsheets can de-duplicate, but the process is fiddly. You remember it is somewhere under Data, then you second-guess whether it keeps the first occurrence or the last, then you discover it treated "Gmail.com" and "gmail.com" as two different values and quietly kept both. For a quick one-off — a list of emails, keywords, URLs, or names you just want unique — opening a spreadsheet is more friction than the job deserves.
Here is how I dedupe lists in a browser, and the three gotchas that trip people up no matter which tool they use.
The basic flow
Paste your list, one item per line, into the Remove Duplicate Lines tool, and it returns only the unique lines. That is the easy part. The interesting part is what "duplicate" actually means — because the answer is less obvious than it sounds.
Gotcha 1: case sensitivity
Is "Apple" the same as "apple"? For a fruit inventory, yes. For a list of case-sensitive identifiers or codes, absolutely not. Most lists you want to dedupe — emails, keywords, names — should be matched case-insensitively, so "John@email.com" and "john@email.com" collapse into one entry. Make sure your tool offers a case-insensitive option and turn it on for anything a human typed.
Gotcha 2: invisible whitespace
This is the one that drives people mad. Two lines look identical, the tool keeps both, and you cannot see why. The culprit is almost always a trailing space, a tab, or a non-breaking space hiding at the end of one line. To the computer, "apple" and "apple " are different strings. The fix is to clean the spacing first: run the list through Remove Extra Spaces before de-duplicating, and the phantom duplicates vanish.
Gotcha 3: order
De-duplication usually preserves the original order and keeps the first occurrence. But if you want to eyeball the result or hand it to someone, a sorted list is far easier to scan. Run the unique list through Sort Text afterwards, and any duplicates that somehow survived become instantly visible, because identical-looking lines end up sitting next to each other.
A clean three-step recipe
For any messy list, this order works every time: remove extra spaces, then remove duplicates with case-insensitive matching on, then sort. Spaces, then uniqueness, then order. Two minutes, no formulas, and it runs entirely in your browser, so a confidential customer list never leaves your machine.
The deeper point: "duplicate" is a decision, not a fact. Decide whether case and whitespace matter for your list before you click, and the tool will do exactly what you expect.