Compare two lists

The job

You have an old attendee list and a new sign-up export, or last month’s keyword list and this month’s. The question is rarely “what changed inside a line” — it is “which whole items are new, gone, or still there”. That is a set comparison, not a text diff.

Why not a line diff

A line-by-line diff reports position changes, so the same item moved to a different row looks like a remove plus an add. Comparing as sets ignores order entirely: “in both”, “only A”, and “only B” are exactly the three groups you usually need.

Turn on case-insensitive matching when the sources disagree on capitalization, and remember the tool trims each line — “Alice ” and “Alice” are the same item.

Limits to know

Matching is whole-line equality after trimming, so near-duplicates like “alice@x.com” and “Alice <alice@x.com>” do not merge. Clean each list first if the formats differ.