Identify unique values between two lists.
As part of a regular website "health check" I was doing for work, I often needed to compare two lists of email addresses to make sure they matched up. Any unique values between the two were a flag for concern, and probably meant there was something wrong with our integrations.
I was initially using a Google Sheet with hacky conditional formatting to do this, but repeatedly fiddling with a spreadsheet got old. Building this simple tool was fun and makes my life just a little bit easier.