Here's a question for you. If your character sees another casting a spell and its effects aren't immediately obvious, can you recognize what spell they're casting? Maybe you also have to be a spellcaster and/or make a successful arcana check? Maybe you need to know what language they're speaking if the spell has a verbal component or see exactly what movements they're making for a somatic component? Might it take an identify or detect magic spell to figure that out? If you need to be a spellcaster to realize what it is, does it need to be on your spell list or you have to know how to cast it yourself? Do you just have to witness the same spell being cast before? I know you don't necessarily have to know what the spell is for the purpose of reacting with a counterspell, but that's more just realizing that a spell is being cast, right? On a related note, can you react with counterspell if the spell is cast with a sorcerer's subtle spell metamagic? I wouldn't think so because that's sort of the point of that ability, but I'm not 100% sure.
Xanathar's Guide to everything has rules for exactly this. Basically, as a reaction, you can make an Intelligence (Arcana) with a DC of 15 + the spell's level, and if it's being cast as a class spell of a class you're a member of, you get advantage (so, typically, if you're druid, you have advantage identifying cure wounds cast by another druid, but if a cleric is casting it, you make a normal roll).
On a related note, can you react with counterspell if the spell is cast with a sorcerer's subtle spell metamagic?
For both recognizing a spell and counterspelling it, it suffices to witness the M component of a spell, which is visual (M components involve touching the component). As a result, subtle spell metamagic will often not work. However, if a spell has no M component, subtle spell will render it componentless, which means you can't tell when someone is casting - and so you can't counterspell it.
For both recognizing a spell and counterspelling it, it suffices to witness the M component of a spell, which is visual (M components involve touching the component). As a result, subtle spell metamagic will often not work. However, if a spell has no M component, subtle spell will render it componentless, which means you can't tell when someone is casting - and so you can't counterspell it.
Here's a question for you. If your character sees another casting a spell and its effects aren't immediately obvious, can you recognize what spell they're casting? Maybe you also have to be a spellcaster and/or make a successful arcana check? Maybe you need to know what language they're speaking if the spell has a verbal component or see exactly what movements they're making for a somatic component? Might it take an identify or detect magic spell to figure that out? If you need to be a spellcaster to realize what it is, does it need to be on your spell list or you have to know how to cast it yourself? Do you just have to witness the same spell being cast before? I know you don't necessarily have to know what the spell is for the purpose of reacting with a counterspell, but that's more just realizing that a spell is being cast, right? On a related note, can you react with counterspell if the spell is cast with a sorcerer's subtle spell metamagic? I wouldn't think so because that's sort of the point of that ability, but I'm not 100% sure.
Xanathar's Guide to everything has rules for exactly this. Basically, as a reaction, you can make an Intelligence (Arcana) with a DC of 15 + the spell's level, and if it's being cast as a class spell of a class you're a member of, you get advantage (so, typically, if you're druid, you have advantage identifying cure wounds cast by another druid, but if a cleric is casting it, you make a normal roll).
For both recognizing a spell and counterspelling it, it suffices to witness the M component of a spell, which is visual (M components involve touching the component). As a result, subtle spell metamagic will often not work. However, if a spell has no M component, subtle spell will render it componentless, which means you can't tell when someone is casting - and so you can't counterspell it.
And here's the SAC entry that says what quindraco said.
"Not all those who wander are lost"