D&D 5E Detecting concentration?

[bedir than]

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.

While that is a valid table implementation, the rules as written do not support

 

[bedir than]

Also, what's cool about the disagreement here is that you can see a couple approaches and decide what is the best fit for the stories at your table.

 

[Jfdlsjfd]

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 wouldn't allow detecting who is concentrating on a spell the PCs in this case. I don't envision concentration as a child concentrating on something, with the tongue sticking out... It's in my mind a low level concentration by the caster, since he is able, without any threat to his concentraiton, to cast a spell that doesn't require concentration, make an attack by fighting in melee (which by itself requires to able to pay close attention to your opponent...) or do any activity except casting another concentration spell, dying or losing a check made when you're hit.

The optional rule where the GM may ask a DC concentration check for other reasons uses the example of "a wave crashing over you while you're on a storm-tossed ship". It's not being bothered by the ship pitching and rolling in a storm, but a wave crashing on you. An immediate death threat of being thrown overboard in the moddle of the ocean => a low DC 10 Con check. So in my opinion, maintaining concentration is a very low intensity task, impossible for (insert magic theory reason) to maintain on two spells but not something that requires any effort otherwise. I can totally see your NPC being able to chit-chat at a social event without giving any clue.

Maybe detecting that something is bothering the NPC while speaking with him as you suggest, but not pinpointing "she's maintaining a spell effect".

 

[Theo R Cwithin]

I wouldn't allow detecting who is concentrating on a spell the PCs in this case. I don't envision concentration as a child concentrating on something, with the tongue sticking out... It's in my mind a low level concentration by the caster, since he is able, without any threat to his concentraiton, to cast a spell that doesn't require concentration, make an attack by fighting in melee (which by itself requires to able to pay close attention to your opponent...) or do any activity except casting another concentration spell, dying or losing a check made when you're hit.

The optional rule where the GM may ask a DC concentration check for other reasons uses the example of "a wave crashing over you while you're on a storm-tossed ship". It's not being bothered by the ship pitching and rolling in a storm, but a wave crashing on you. An immediate death threat of being thrown overboard in the moddle of the ocean => a low DC 10 Con check. So in my opinion, maintaining concentration is a very low intensity task, impossible for (insert magic theory reason) to maintain on two spells but not something that requires any effort otherwise. I can totally see your NPC being able to chit-chat at a social event without giving any clue.

Maybe detecting that something is bothering the NPC while speaking with him as you suggest, but not pinpointing "she's maintaining a spell effect".

I agree. The way spell concentration is described interacting with other actions makes me think it's more like a physical [insert arcano-babble here] overload limit on the caster's "mana gland" rather, than genuine mental effort.

If it comes up (and only if it comes up), I think the suggestion to treat it as an Insight vs Deception is a solid one, both as RAW and as a better story device. And she's a shape-shifter, so deception is kind of her thing.

 

[Perun]

I might use a high-DC Spot or Investigate check (depending on a situation), if the PCs are just participating at a social event. I might use a (slightly lower DC) Insight check if they're actively engaging in conversation with the NPC concentrating on a spell. With this check they'd be able to determine there's something else that's occupying the NPC's mind. In a social situation, the character in question might take a split second longer than is normally necessary to answer questions, laugh at jokes, might be sweating slightly, etc. That could mean they're concentrating on a spell, but also a lot of other reasons (preoccupied about a sick child/spouse, suffering from tooth-/stomachache, lost a lot of money on a gamble, etc.). Following that, an Arcana check would be able to confirm the character is indeed concentrating on a magical effect (as there could be barely noticeable effect that a trained individual might notice). Just IMO, of course

 

[Coroc]

Is there a RAW way to tell if a caster is concentrating on a spell?

I've just assumed an Insight or Arcana check or something, but can't find a specific rule for it.

A few situations to illustrate:
PCs try to discern if a sketchy NPC is concentrating on a charm or scry or something during a negotiation.
PCs want to determine which enemy caster to target in order to drop an ongoing debuff affecting them.

Poke him with a stick

 

[dave2008]

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.

That is not exactly true, here is the section @bedir than is talking about.

Notice that is says you can identify a spell that has already been cast, and it says: "If the character perceived the casting, the spell's effect, or both, the..."

Now, that doesn't say you can identify the caster, but if you can identify a spell, you might be able to deduce the caster.

 

[Fenris-77]

Easy-peasy. Just start punching feast guests in the nose until the elementals disappear. Presto, threat eliminated and villain found. Sometimes the Barbarian answer is the correct answer.

 

[BluejayJunior]

I would lean towards no, you cannot detect if someone is concentrating on something. In my opinion, it is far to close to Detect Magic. A skill check shouldn't be able to replicate a spell. Even if it is a weaker version of it, being able to detect concentration would be a massively huge boost in any kind of social situation or when someone has magically disguised themselves.

 

[aco175]

Doesn't the PHB say you can maintain concentration while attacking? This would seem to me that it is rather easy to maintain and does not use too much of your effort.