Compare Two Lists

Comparing two lists by eye is slow and error-prone. Paste two lists, such as last month’s and this month’s customers, an invitation list and the RSVPs, or two exports from different systems, and this tool sorts every item into the right bucket: in both lists, only in A, only in B, the merged list without duplicates, and items that appear in just one list. It can ignore capital letters and stray spaces, and it reports items repeated inside each list.

How to use this tool

1. Paste the first list into List A and the second into List B.
2. Choose how items are separated: lines, commas, tabs or spaces.
3. Decide whether “Apple” and “apple” should count as the same item.
4. Copy whichever result you need: in both, only in A, only in B, union or difference.

Formula

Both = A ∩ B · Only A = A − B · Only B = B − A · Union = A ∪ B · One list only = (A − B) ∪ (B − A)

These are the standard set operations. Each list is first reduced to its unique items; with “ignore case” two items match when their lower-case forms are equal, and with “ignore spaces” leading and trailing spaces do not count. Text is Unicode-normalised (NFC), so an accented letter typed in two different ways still matches. Results keep the order in which items first appear, or can be sorted A to Z with numbers in natural order (item2 before item10).

Example

With the default lists, A has 5 entries (banana appears twice, once as Banana) and B has 4. In both: banana and date. Only in A: apple and cherry. Only in B: fig and grape. The union has 6 unique items, and the duplicates table shows banana twice in list A.