About Left-Exclusive Join
Left-Exclusive Join returns the items present in List A but not in List B — the set difference A − B. Paste both lists (one item per line) and the tool emits only the values that appear in A and are absent from B, preserving the order from List A.
Use this whenever you have a reference list and a comparison list and need to know what is missing from the comparison. Common scenarios: which users in a customer export are not yet in your CRM (export = A, CRM = B), which files in last week's build are no longer in this week's, which licences listed in LICENSE are not yet referenced in THIRD_PARTY_NOTICES.md, which followers you lost between two snapshots. The operation is asymmetric: A − B and B − A produce different results — for the mirror direction, use Right-Exclusive Join.
Examples
List A:
apple
banana
cherry
date
List B:
cherry
date
elderberry
figapple
bananaItems present in A but missing from B. To find items only in B, use Right-Exclusive Join instead.
Frequently asked questions
Why are there separate tools for left-exclusive and right-exclusive?
Because the operation is asymmetric. A − B (items only in A) and B − A (items only in B) produce different results. Having two tools means you stay in your head about which list is which, instead of remembering to swap inputs every time you flip the question.
What if I want both directions at once?
Use Full-Exclusive Join, which returns items unique to either list — equivalent to running both Left-Exclusive and Right-Exclusive and combining the results into one output.
How does it handle duplicates within List A?
Duplicates inside List A are collapsed: each unique value appears at most once in the output. Duplicates inside List B do not affect the result, since List B is only consulted to test membership.
What if List B is empty?
Every unique item from List A is returned, since none of them are in B. This is a useful sanity check before pasting in larger inputs.