Compare Two Lists

Compare Two Lists takes two lists of items - email addresses, SKUs, usernames, IDs, URLs, anything one-per-line - and answers the membership questions you have about them: which items appear in both, which are only in the first, which are only in the second, and which are duplicated within a single list. It is set arithmetic with a UI, running instantly on lists of thousands of items.

You can check how it works to compare two lists online in a few seconds. Click Load Sample, then Compare. List A has six email addresses and List B has five. In Both shows bob, carol and erin, because [email protected] in List B matches [email protected] in List A when case is ignored. Only in A shows alice and dave, Only in B shows frank and grace, and Duplicates in A shows bob, who is listed twice. That is how to compare two lists for differences without losing the repeats.

This is not a line-by-line diff. A diff cares about order and position, so moving one line makes everything below it look changed. This tool treats each list as an unordered bag of items, which is the right model when you are reconciling an export from one system against an export from another. Row 300 in your CRM export has no relationship to row 300 in your billing export; the only thing that matters is whether the value exists on both sides. If you want a positional, side-by-side comparison of prose or code, use the Text Diff Checker instead.

Everything runs in your browser. That matters more here than for most utilities, because the lists people compare are usually the sensitive kind - customer emails, employee IDs, license keys, account numbers. Nothing is uploaded, so pasting a subscriber export into this page carries none of the risk of pasting it into a service that processes it server-side.

The comparison is set-based, so an item appearing three times in one list is one member of that set. That is why duplicates within each list are reported separately rather than folded into the result: knowing that a list has repeats is usually as useful as knowing what the two lists share. Case-insensitive matching compares in a normalised form while preserving what you typed in the output.