About Inner Join Two Lists
Inner Join Two Lists returns the items that appear in both List A and List B — the set-theoretic intersection. Paste two lists (one item per line); the tool deduplicates within each list and emits only the values present on both sides. Output preserves the order in which items first appear in List A.
This is the operation you reach for when you need to find overlap between two collections: shared email addresses across two mailing lists, dependencies that appear in both package.json files, customer IDs present in two databases, or feature flags enabled in both staging and production. Because everything happens in your browser, you can paste sensitive identifiers without worrying about them being uploaded. For the opposite question — items that appear in only one list — use Full-Exclusive Join.
Examples
List A:
apple
banana
cherry
date
List B:
cherry
date
elderberry
figcherry
dateOrder follows the first occurrence in List A.
Frequently asked questions
Are duplicates within a single list counted?
No. Each list is treated as a set, so an item that appears three times in List A and once in List B will appear once in the output.
Is the comparison case-sensitive?
Yes by default — `Foo` and `foo` are treated as distinct items. Use the case-insensitive option in the comparison bar if you need to match across case.
What if the lists are very different sizes?
Size does not matter. The intersection is the same whether one list has ten items and the other has ten thousand; only the items common to both ever appear in the output.
How is this different from Full-Inclusive Join?
Full-Inclusive Join returns the union — every item from either list, deduped. Inner Join returns only the items that appear in both. They are at opposite ends of the spectrum: inner keeps the smallest possible set, inclusive keeps the largest.