D&D 5E Detecting concentration?

[bedir than]

By XGtE you MUST observe the casting components of the spell while it is being casted(V,S,M) or spell has visible effects. It says that it is impossible to determine the caster of a spell that is in effect.

This isn't in the language of the three paragraphs on page 85

 

[Krachek]

The problem when you allow such move, because sometime it seem appropriate for the situation, is that your players gonna ask for it forever and every single fight and new pc the see.

 

[Horwath]

This isn't in the language of the three paragraphs on page 85

Last sentence in 1st paragraph under Spellcasting:

If an imperceptible casting produces a perceptible effect,
it's normally impossible to determine who cast the
spell in the absence of other evidence.

 

[bedir than]

Last sentence in 1st paragraph under Spellcasting:

If an imperceptible casting produces a perceptible effect,
it's normally impossible to determine who cast the
spell in the absence of other evidence.

That paragraph is a specific rule regarding Subtle Spell and Innate Spellcasting, and doesn't mention anything about Concentration.

 

[ad_hoc]

The problem when you allow such move, because sometime it seem appropriate for the situation, is that your players gonna ask for it forever and every single fight and new pc the see.

I don't see the problem.

 

[Horwath]

That paragraph is a specific rule regarding Subtle Spell and Innate Spellcasting, and doesn't mention anything about Concentration.

It says that if you do not recognize the act of spellcasting, you cannot determine the caster after.
By that you can conclude that concentration has no visible clues.

 

[bedir than]

It says that if you do not recognize the act of spellcasting, you cannot determine the caster after.
By that you can conclude that concentration has no visible clues.

That paragraph starts by saying "If the need for a spell's components has been removed..."

Since, that is not the case for most spells with concentration there is no reason to think that spells that are being concentrated on are impossible to identify.

Let's say you are concentrating on Immolation. How in the world would someone not be able to identify that?

 

[MarkB]

If the caster isn't trying to hide the fact that they're concentrating, I'd make it a very easy DC or just automatic. If they are, I'd run it as a simple Insight vs. Deception.

I'd still allow for possible false positives. If someone's concentrating on something else, like listening in on a nearby conversation or doing some mental arithmetic, it's probably not going to look much different than concentrating on a spell.

 

[Horwath]

That paragraph starts by saying "If the need for a spell's components has been removed..."

Since, that is not the case for most spells with concentration there is no reason to think that spells that are being concentrated on are impossible to identify.

Let's say you are concentrating on Immolation. How in the world would someone not be able to identify that?

they would see someone on fire, and if they are schooled in magic, they might recognize it as a spell, but they would not know who caused it if they didn't see/hear spellcaster casting that spell.

 

[Theo R Cwithin]

Thanks for all the advice, and for the XGtE hints. Very helpful stuff for a newbie 5e GM!

The situation is this:
Before the scene (a banquet), an enemy NPC privately conjures a bunch of little elementals. She instructs them to remain hidden until a particular cue (a bell to start the meal), then burst out and attack everyone in sight. By the time the cue happens, that NPC will likely be conversing with the PCs.

In this case, it sounds like there's not really a way for the PCs to tell specifically if the caster is concentrating on the conjuration, since they don't see her cast it and she doesn't otherwise interact with the elementals. If the players get suspicious for some reason, their PCs can roll an Insight check to see if she's hiding something, even if they don't know what.

I like that. It keeps it in the realm of the NPC's motives rather than her mechanics.