The limits Google actually enforces
A responsive search ad accepts up to 15 headlines and 4 descriptions, and Google assembles them into combinations on the fly. The caps are hard, so anything over them simply will not save:
- Headlines: 30 characters each, 3 minimum, 15 maximum. Spaces count.
- Descriptions: 90 characters each, 2 minimum, 4 maximum.
- Display path: two fields of 15 characters each, after your domain.
Google scores an ad on how much room it has to test, so filling all 15 headline slots with genuinely different angles beats filling five slots with careful ones. The headline generator exists to get you to 15 without counting characters by hand.