Merge Two Lists & Remove Duplicates
Paste two lists to get one clean deduplicated list — plus a count of the overlapping entries that were collapsed.
About this tool
Merge Two Lists & Remove Duplicates combines your two lists into a single, clean list with every duplicate collapsed — the set union of the two — and tells you exactly how much overlap it removed. It's the fast way to consolidate two exports of anything: email subscribers, customer IDs, SKUs, domains, tags, package names, or feature flags into one deduplicated list you can copy straight out.
The totals line reports each list's size, the merged size, how many duplicates were removed, and how many entries were shared by both lists (the cross-list overlap) — the headline number when you want to know how much two lists have in common.
Everything runs locally in your browser — nothing is uploaded.
Worked example
List A
apple
banana
cherry
List B
banana
cherry
date
Merged list
Merged (4):
apple
banana
cherry
date
Totals: A=3 · B=3 · merged=4 · duplicates removed=2 · shared by both=2
The two lists had 6 entries between them; banana and cherry appeared in both, so they were
collapsed to one each. The result is 4 unique items, 2 duplicates removed, and 2 entries shared
by both lists.
Options
- Separator — split each list by new line (default), comma, tab, semicolon, pipe, or space.
- Merge order — Append puts all of List A first, then List B (default); Interleave alternates A, B, A, B… When the same item appears twice, the first occurrence is the one kept, so merge order decides which list's copy (and its exact spelling/case) survives.
- Trim whitespace — strip leading/trailing spaces before comparing (on by default).
- Ignore blank items — drop empty lines (on by default).
- Ignore case — treat
Appleandappleas the same item (the kept copy shows the first occurrence's original case). - Sort order — keep the input order (default), or sort the merged list A→Z or Z→A.
- Ignore leading zeros — match
007with7, handy for numeric IDs.
Limits
- Up to 100,000 items per list.
- Deduplication is always on — that is the whole point. To see which items are only in A, only in B, or shared, use a set-difference tool instead; this tool produces the combined list.
- Items are compared as-is (after the options above) — there is no fuzzy or partial matching, so
appleandapplesstay distinct. - The merged list is joined one item per line for readability, whatever separator you split on.
FAQ
How is this different from just comparing two lists?
A comparison (set-difference) tool shows you three buckets — only in A, only in B, and shared. This tool does the opposite job: it gives you the single combined list with duplicates removed (the union), which is what you want when you're consolidating two exports into one. The totals line still tells you how many entries the two lists shared.
What does "duplicates removed" versus "shared by both" mean?
Duplicates removed is every entry that was collapsed, including repeats within a single
list and matches across the two lists — it always equals A + B − merged. Shared by both
counts only the distinct entries that appeared in both List A and List B (the cross-list
overlap). If neither list has internal repeats, the two numbers match.
How do I merge comma-separated or tab-separated lists?
Change the Separator dropdown to Comma, Tab, Semicolon, Pipe, or Space. Both lists
are split the same way, so paste them in whatever format you have — one item per line is the
default. The merged output is always joined one item per line.
Which copy is kept when an item appears in both lists?
The first occurrence wins, so Merge order decides it: with Append, List A's copy is kept;
with Interleave, whichever list reached that item first. This matters with Ignore case
on — a shared [email protected] keeps the capitalization of the copy that appeared first.
Can it match items that differ only by case or leading zeros?
Yes. Enable Ignore case to treat Apple and apple as the same item, and Ignore leading
zeros to treat 007 and 7 as equal — useful for consolidating numeric IDs, order numbers, or
SKUs that were exported with different zero-padding.
Is my data uploaded anywhere?
No. The merge runs entirely in your browser via WebAssembly — your lists never leave your device.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool list-dedupe-merge "apple
banana
cherry" 'list_b=banana
cherry
date'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/list-dedupe-merge/?list_a=apple%0Abanana%0Acherry&list_b=banana%0Acherry%0Adate&separator=newline&merge_order=append&trim=true&ignore_blank=true&ignore_case=true&sort=input&ignore_leading_zeros=trueMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.