Just a note in case anyone is worried I’m adding a mage to every encounter, I very rarely use counterspell against my players; it’s one of the spells I consider to have high “fun-ruining” potential.
I’m struggling a bit to decide on how to handle this interaction in a way that feels fair. From my understanding RAW, a character doesn’t know what spell is being cast. I think you can use your reaction to make an arcana check to discern it, but of course then you can’t counterspell it. For enemy spellcasters I generally describe what’s being cast, instead of naming the spell right away, but it can slow combat down, and is a bit one-sided since when a player casts a spell they lead with “I cast X”. This leads to an imbalance where I’m aware of what’s needed to counterspell something while the players are not, and can cause some awkwardness trying to decide how to play around that without metagaming.
I can think of a few different ways to handle this, each with its own drawbacks, but I’m curious to hear what y’all do at your tables!
I’m aware of people who decouple the “cast a spell” step from the “announce the spell” step, and implement rules to identify which spells are being cast ahead of time. I think it slows the game down too much for my liking, but that’s an option.
To make Counterspell more fair and give it a degree of interaction, I run counterspell as a contested check (d20 + spellcasting modifier + level of the spell/counterspell). It gives players an active role in the outcome, and it feels less cheap when the NPC negates their spell.
Oh now that’s an interesting house rule. That actually gives me an idea for situations where you upcast counterspell but it still requires a check RAW: adding a bonus for the level of the upcast. So if a 6th level spell is cast, and a 5th level counterspell comes out in response, the counterspell caster can add another +2 to their D20 + spellcasting ability check