What is this list diff tool?
A free, browser-based tool that compares two lists and shows you exactly how they differ. Paste one item per line into list A and list B, and it splits them into three sets: items only in A (A−B), items only in B (B−A), and items in both (A∩B) — each with a count. You can match case-insensitively and ignore surrounding whitespace, and copy or download any of the three sets. Everything runs locally in your browser, so your data is never uploaded.
How to use it
- Paste your two lists (one item per line) into List A and List B on the left.
- Toggle case-insensitive matching and whitespace trimming as needed.
- Read the A−B, B−A, and A∩B blocks on the right, then copy or download each one.
Common use cases
- Building an email suppression list — subtract unsubscribed, bounced, or already-mailed addresses (B) from your target list (A) to get A−B.
- Finding new signups by comparing today's export (B) against last week's (A) and reading B−A.
- Checking the overlap between two segments or audiences with A∩B.