Each app has a settings screen that takes your keys. They are stored
locally on your own machine — never sent to our servers, never in our
database.
Each key is validated with a real call, so a field cannot quietly accept
something that does not work and leave you to find out later.
When a key is missing, wrong or out of quota, the app names the key that
failed and what to do about it. It does not degrade quietly and hand you a thinner
report with no explanation.
First run walks you through adding them, because the app does nothing at
all until they are in.