The Counterspell feat lets spellcasters counteract a foe that is Casting a Spell, as long as they have the spell prepared and they can see it being cast, via expending that same spell. What if an enemy casts a cantrip? Would a spellcaster be able to Counterspell using that same cantrip?
Assuming the spellcaster has that spell prepared and can see it being cast, they'd be able to meet all the requirements of the Counterspell – they "lose [their] spell slot as if [they] had cast the triggering spell", which is to say that no spell slot would be lost because cantrips do not use spell slots, and they could then attempt to counteract. Would this work, rules as written?
Additionally, Clever Counterspell lets you use a different spell besides the one being cast as long as it shares a trait (or has an opposing trait) with the spell being cast. If cantrips work for Counterspell, would they work for use with Clever Counterspell?
Best Answer
No
The phrasing in Counterspell reads:
Cantrips are not spell slots and neither can they be "expended". So they are not valid for Counterspell, and therefore also not valid for Clever Counterspell (although you could Clever Counterspell an enemy cantrip by expending your own spell slot). Further, the Cantrip rules seem to reinforce this connection: