Deduplicating Any List
Paste a list and this tool removes lines that repeat, reporting how many it stripped. Case-insensitive matching is on by default, so “Apple” and “apple” are treated as the same entry — toggle it off if case is meaningful in your data.
This is the general-purpose version of a job that comes up constantly: keyword lists, URL lists, email exports, product SKUs, redirect mappings. Any time you combine two sources you get duplicates, and any time you have duplicates something downstream gets distorted.
Case-insensitive or not
The default treats case as insignificant, which is right for most text lists. Keywords, email addresses, domain names and most human-entered data are conceptually the same regardless of capitalisation.
Turn it off when case carries meaning. Product SKUs, API keys, file paths on case-sensitive systems, and programming identifiers can all legitimately differ by case alone, and collapsing them would destroy data.
If you are unsure, run it both ways and compare the removal counts. A large difference means your list has case variants worth looking at before deciding.
How matching works
Each line is trimmed of leading and trailing whitespace before comparison, so a line with a stray trailing space still matches its clean twin. This catches the most common invisible difference in pasted lists.
Blank lines are preserved rather than deduplicated, so any spacing structure in your list survives. Only non-empty lines are compared.
The first occurrence of each line is kept and later ones removed, so the original ordering of your unique entries is preserved. That matters when the list order is meaningful — a priority list, a redirect mapping, a sequence of steps.
Where duplicates cause real problems
- Redirect mappings — duplicate source URLs produce conflicting rules, and which wins depends on server configuration rather than intent.
- Sitemaps — the same page listed twice sends a contradictory canonical signal and wastes crawl requests.
- Keyword research — duplicates inflate topic counts and distort a content plan sized by keyword volume per topic.
- Email and contact lists — sending the same person twice is a visible mistake and can trigger spam complaints.
- Import files — many systems fail an entire import on a duplicate key rather than skipping the row.
Specialised alternatives
For URLs, the URL Deduplicator is a better fit than this tool. It normalises protocol, hostname case and trailing slashes before comparing, so http://Example.com/page/ and https://example.com/page are recognised as the same page — which plain line matching would miss entirely.
For keywords, the Keyword Deduplicator collapses whitespace inside entries as well as around them, so “running shoes” with a double space matches “running shoes”.
Use this general version for everything else, or when you specifically want plain line-by-line matching without any normalisation applied.
Cleaning before deduplicating
Inconsistent whitespace is the most common reason a deduplicator appears not to work. Lines differing only by an internal double space are genuinely different strings, so they survive. Running the Remove Extra Spaces tool first normalises internal spacing and usually removes more duplicates than the deduplicator alone.
Sorting afterwards makes the result easier to verify. The Sort Keywords Alphabetically tool works on any line-separated list, and sorting puts near-duplicates that the tool deliberately kept next to each other where you can see them.
Privacy
Everything runs in your browser. Nothing you paste is transmitted or stored, which matters for the kinds of list this tool is used on — contact exports, client keyword research, internal URL inventories.
Frequently asked questions
Does it preserve the original order?
Yes. The first occurrence of each line is kept and later repeats removed, so the ordering of your unique entries is unchanged. That matters for priority lists and redirect mappings where order is meaningful.
When should I turn off case-insensitive matching?
When case carries meaning — product SKUs, API keys, case-sensitive file paths, programming identifiers. For ordinary text lists like keywords and email addresses, leave it on.
Why are some obvious duplicates not removed?
Usually inconsistent internal whitespace. “running shoes” with a double space is a different string from “running shoes”. Run the text through Remove Extra Spaces first to normalise internal spacing.
Should I use this for URLs?
The URL Deduplicator is better, since it normalises protocol, hostname case and trailing slashes before comparing. Plain line matching treats http and https versions of the same page as different entries.
Are blank lines removed?
No, they are preserved so any spacing structure in your list survives. Only non-empty lines are compared for duplicates.