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!
So, RAW here is how a round with a spell is supposed to work:
RAW, Counterspell would occur during that second step. The creature that casts it has no idea what the spell they’re countering is, beyond context clues (i.e. they’ve seen that armored spell caster has been casting spells that heal their allies earlier).
As you said, there are rules to identify a spell. They were added by either Tasha’s Cauldron of Everything or Xanathar’s Guide to Everything. A character can use their Reaction to identify the spell. This usually means you’ll need 2 spellcasters working in conjunction for Counterspell to work with an identified spell.
As for how I run it at my table: I don’t. I really don’t like it. It’s anti-fun, and the awkward pause and wording that’s required to cast spells in case someone wants to counter it. There’s some equally awkward metagaming thats required if someone accidentally blurts out the name of the spell, and it plays really poorly with how most VTT software handles spells (most just spit them out in the chat for everyone to see). It is just so un-fun that I just ban the spell outright at my table and it makes everything much simpler.
Having said that, if I do play at a table where it isn’t banned, we usually go about it as I described above. The Reaction needed to identify the spell is an intentional design decision to prevent spellcasters from identifying every spell cast their way before deciding to counter them, and needing 2 spellcasters to work together to “cleanly” cast it is perfectly fine, in my opinion. Spellcasters are already bonkers in this game, there’s no reason to empower them further by letting them save-up their Counterspells until they’re absolutely critical.
It’s just important that every player is on the same page and doesn’t blurt-out their spell names whenever they cast a spell.
I like giving all my spells new names (for example, I was playing a cleric who worshipped the god of bees. Cause light wounds was “sting” in my spellbook) if the dm is down with it. Gives that layer of abstraction and lets me add flavor.
Yeah from what I know it’s one of the more commonly banned spells. Personally I just don’t like the idea of banning published content. Making an effort to keep things mysterious until the spell is actually taking effect is a bit cleaner of a solution, and I do like the teamwork aspect of a RAW spell identification + counterspell