Duplicate Line Remover

Okay, real talk. I was merging email lists from three different newsletter platforms last year (don't ask why I was using three), and I had like 47,000 lines with probably 15,000 duplicates. Excel kept crashing. Google Sheets was laughing at me. I spent an entire afternoon manually scrolling through trying to spot dupes before I realized I was going insane.

So I built this tool out of pure spite.

And honestly? It's become one of my most-used tools. I use it for *everything* now—cleaning scraped data, deduping CSV exports, organizing tag lists, you name it. If you've ever copy-pasted data from multiple sources and ended up with a mess of repeated lines, you know exactly what I'm talking about.

When you actually need this

You know what drives me crazy? When you export data from three different systems and merge them into one master list, and suddenly you've got the same email address showing up six times. Or when you're pulling log files from multiple servers and half the error messages are identical.

Here's where I use this constantly:

Email list merging—this is the big one. Every time I consolidate newsletter subscribers or combine contact lists from different campaigns, there's duplicates everywhere. Last month I had 8,500 lines and 3,200 turned out to be dupes. Saved me hours of manual cleanup.

CSV data exports—database exports *always* have duplicate rows (why does this happen so often?). Whether it's product SKUs, customer IDs, or transaction records, I paste it here first before doing anything else with it.

Log file analysis—server logs repeat the same error messages hundreds of times. I just want to see the unique errors, not scroll through 500 identical lines saying the same thing crashed.

Content tagging—when I'm organizing blog tags or product categories and I've copy-pasted from different sources, duplicates sneak in. This cleans them up in like two seconds.

The tool works fine up to 100k+ lines in my testing (I tried a massive log file once just to see), though your browser might get a little slow if you're pushing really huge datasets. For normal use—under 50k lines—it's basically instant.

Why duplicates are so annoying

Maybe I'm just lazy, but manually finding duplicates in a list is one of those tasks that makes me want to quit computers entirely. Your eyes glaze over after the first hundred lines and you start missing obvious dupes.

Excel has that "Remove Duplicates" feature, sure—but it's buried in menus, it doesn't show you what it removed, and if you have a huge dataset it freezes for like 30 seconds. Plus you need to save the file, which means if you just want to quickly clean some data you copied, it's overkill.

Google Sheets is even worse for this. Ever tried to dedupe 10,000 lines in Sheets? It just sits there spinning. Sometimes it times out entirely.

This tool just... does it. Instantly. You paste, it processes, you copy. No saving files, no waiting, no menu diving.

How the options work

I added three options based on what I kept needing (and what people kept asking for):

Case sensitive—by default, "Apple" and "apple" are treated as the same line and one gets removed. If you turn case sensitivity *on*, they're treated as different. I use this when I'm working with code or product names where capitalization actually matters. A lot of people ask if this preserves the order of lines—yes, it keeps the first occurrence exactly where it was and just drops later dupes.

Remove empty lines—this is on by default because blank lines in data are usually just noise from copy-pasting. But sometimes you actually *want* to keep blank lines (like when you're formatting paragraphs), so you can toggle it off.

Sort alphabetically—after deduping, this sorts everything A-Z. Super useful when you're making an organized list. I turn this on when I'm cleaning up tag lists or creating alphabetical indexes. Off by default because sometimes the original order matters (like when you're deduping a log file and the chronological order is important).

The tool runs entirely in your browser—nothing gets uploaded to a server. All the processing happens locally with JavaScript. I could've built a backend for this but honestly it's unnecessary, and this way it works offline too.

Tips I've learned

Combine this with the Word & Character Counter when you need to see line counts before and after deduplication. I do this all the time when I'm prepping data reports and need to document how much cleanup I did.

If you're working with CSV data that has multiple columns, this tool only looks at entire lines—so "john@email.com,John,Smith" and "jane@email.com,Jane,Doe" are treated as completely different even if you only care about deduping email addresses. For that kind of thing you'd need to isolate just the email column first (or use the Email Extractor to pull out just the emails).

One mistake I made early on (before I added the stats at the bottom): I wasn't checking *how many* duplicates were getting removed. Now the tool shows you exactly how many unique lines remain and how many dupes were dropped. This matters because sometimes you expect like 10 dupes but you're actually getting 3,000 removed, which might mean there's a problem with your source data.

The case sensitivity thing surprised me—I initially had it *on* by default, but turns out most people doing email list cleanup want case-insensitive matching because "John@Email.com" and "john@email.com" are the same person. I switched the default based on that feedback.

Final thoughts

Look, I'm not going to pretend this is rocket science—it's a pretty simple tool. But that's kind of the point? Not everything needs to be complicated.

Sometimes you just need to paste some messy data, clean it up in two seconds, and get back to what you were actually doing. No sign-ups, no downloads, no waiting. Just paste, dedupe, copy.

I probably should've built this years earlier—would've saved me so many headaches. But hey, better late than never, right?

If you find bugs or have feature requests, ngl I'm always tweaking these tools based on what people actually need (that's how the sort option got added tbh). The whole point of Tool Vault is making utilities that solve real problems without the usual web app bloat.