@JeremyECrawford PHB 201 says: "A cantrip is a spell that CAN be cast […] without a spell slot".

Can you voluntarily spend a spell slot on a cantrip? (For instance, to protect it from Counterspell?)

Obviously, there would be no other benefits / damage bonuses.

Thank you! <3

— fek (@fekfekfekfek) October 10, 2018

A cantrip never uses a spell slot. #DnD https://t.co/RiI6gxWIto

— Jeremy Crawford (@JeremyECrawford) October 10, 2018