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If an NPC is telling the truth, what's the Insight DC to know they're telling the truth?

I believe that should be a persuasion roll for the NPC, with a base DC of 10. You can decrease the DC to something as low as an automatic success (DC 0) if characters are in friendly terms, or increase it up to a DC of 20 if the interaction happens under an atmosphere of strong hostility.

EDIT: I would also apply the PC's insight skill as a negative modifier to the persuasion roll. Insightfulness should make you more adept at detecting sincerity.
 
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GlassJaw

Explorer
If a PC asks to roll Insight against an NPC telling the truth, I say "you don't suspect he's lying" or "he seems to be telling the truth" - something along those lines - regardless of what the PC rolled.
 

GlassJaw

Explorer
I believe that should be a persuasion roll for the NPC, with a base DC of 10. You can decrease the DC to something as low as an automatic success (DC 0) if characters are in friendly terms, or increase it up to a DC of 20 if the interaction happens under an atmosphere of strong hostility.

EDIT: I would also apply the PC's insight skill as a negative modifier to the persuasion roll. Insightfulness should make you more adept at detecting sincerity.
The only time I roll a social skill for an NPC opposed by a PC is Deception. A player is always the final arbiter as to whether their character is persuaded or intimidated.
 

iserith

Explorer
I likely don't set a DC. The character succeeds, no roll, perhaps because the truthful NPC exhibits no body language, speech habit, or change in mannerisms that suggest a deception.
 

Charlaquin

Explorer
I likely don't set a DC. The character succeeds, no roll, perhaps because the truthful NPC exhibits no body language, speech habit, or change in mannerisms that suggest a deception.
This. If an NPC is telling the truth, they exhibit no signs that they are lying, therefore there is no uncertainty if a PC attempts to discern whether or not they are lying by observing their behavior.

This is yet another reason why using a skill to "detect" truth or lies is a terrible idea.
And this. When an NPC lies to a PC, I roll for the NPC against the PC’s passive Wisdom (Insight). On a failure, I tell the PCs what they notice - for instance, that the NPC is having difficulty maintaining eye contact and their brow has a faint glimmer of sweat or something. On a success, I let the NPC’s statement stand on its own. In either case, it is up to the player whether their character believes they are being lied to or not.
 

jgsugden

Explorer
This is the way I do it:

When a PC attempts to use a skill without spending an action, they generally do so "passively", meaning they add 10 to their skill and use that as the result (with a +/- 5 for advantage/disadvantage). If they take an action to perform the skill, they get to roll a d20, but their "passive" score is a floor for their result unless there is time pressure or other challenges that make things difficult.

When a player wishes to sound convince someone they are being honest, they may roll deception or persuasion rolls. For persuasion, sounding sincere when telling the truth is DC 15 or the observers passive insight, whichever is lower. For deception, the DC is the observer's passive insight.
 
Insight is great for noticing if an ally is charmed and acting strangely. If you know the person, you get advantage on your passive check or roll.

Regarding the OP:
If a PC is unsure whether an NPC is being honest but that NPC is actually being honest, I roll the dice behind the dm screen and then Tell the player the truth that NPC seems to be sincere. I don’t even bother looking at the dice roll. I like adding that little bit of uncertainty. The fact that they are asking for a roll shows they are suspicious. Either the player will learn to trust the NPC (because of in game actions)or they won’t but I won’t just tell him, “oh yeah, he’s totally trustworthy.”
 

Charlaquin

Explorer
If a PC is unsure whether an NPC is being honest but that NPC is actually being honest, I roll the dice behind the dm screen and then Tell the player the truth that NPC seems to be sincere. I don’t even bother looking at the dice roll. I like adding that little bit of uncertainty.
Query: It would seem to me that not looking at the die before announcing the result would remove the uncertainty that you roll the die in order to add; is this a bug or a feature of your approach?
 

5ekyu

Explorer
I've been setting it as their 'Passive Deception' DC. What do you do?
I dont. Insight checks can give you intentions (I use it as disposition), signs of deception, etc.

If the target is not being deceptive, then I generally assign it as a DC based on circumstance and using the persuasiveness of the speaker usually between 10-20. Someone who is **bad** at social stuff may well give off signs/tells of lying even when they arent.

Any failed ability check can yield a setback, after all.
 

Ristamar

Explorer
As a DM, I prefer to roll Deception vs Passive Insight if I feel an NPC may be giving signs (s)he's not being entirely truthful or genuine. If a PC presses or revisits the NPC's deceptive key points or has information/evidence that could help expose deception, I may roll with disadvantage or grant advantage to their Passive Insight, respectively.

In short, it's not a skill that players have to actively roll during a conversation.
 
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Imaculata

Explorer
Insight isn't a lie detector, and neither is sense motive in older editions.

When an npc lies, you generally can't tell, unless the DM decides that the npc exhibits a remarkable behavior. And if that be the case, a player can ask wether they can tell what this behavior means... and then (possibly) you roll insight against the npc's deception to determine what it means, but not wether the npc lies. The players may be able to deduce some things that give them a clue regarding whether the npc is telling the truth, but it is still up to them to interpret it how they wish.

For example, an npc might be throwing a suspicious look at someone else at the bar. Determining what that means would require an insight check.
Or, an npc may be making a secret gesture at another npc, again, roll insight.
Or, an npc may be acting a bit skittish or nervous. Determining why he is acting this way, if this can be determined by just looking at him, may require an insight check.
Or, an npc may be bluffing, and the players may ask to check this with an insight check... but maybe it is impossible to determine, that is up to the DM.

Generally speaking, when I have an npc lie to my players, he does so in a way that is not obvious to them at all by any means... unless he is really bad at it, and I want him to get caught.

Example of insight from play:

DM: While talking to the barmaiden, you notice one of your companions is looking a bit agitated.
Player: Can I tell why she is behaving this way?
DM: Roll insight.
Player: 15!
DM: She seems to be a bit jealous, and about to pick a fight with the bar maiden.
Player: I do not intervene and just enjoy the show.

Example of lying from play:


Npc: One word and I will rain hell down on you and your friends. You are on my turf now, and me and my pals have you vastly outnumbered, surrounded and are better armed. You would do well to lay down your weapons, if you value your lives.
Player: Can I tell if he is telling the truth?
DM: He seems to mean what he says. What are you looking for specifically?
Player: Can I tell if other people in the tavern are on his side?
DM: Make an insight check.
Player: 15!
DM: You notice everyone in the bar is watching you and your friends carefully, and a few shady characters in the tavern seem to have their hands on a weapon tucked underneath their cloak. It seems he is not alone, but whether your party is also outnumbered, you do not know.
 
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Sadras

Explorer
This is yet another reason why using a skill to "detect" truth or lies is a terrible idea.
And this. When an NPC lies to a PC, I roll for the NPC against the PC’s passive Wisdom (Insight). On a failure, I tell the PCs what they notice - for instance, that the NPC is having difficulty maintaining eye contact and their brow has a faint glimmer of sweat or something. On a success, I let the NPC’s statement stand on its own. In either case, it is up to the player whether their character believes they are being lied to or not.
There appears to be some confusion, you agree with Elfcrusher but then in your example, you provided lying clues thereby treating the Insight skill as a detect lie check. I do understand that you took the "detect lie roll" behind the DM screen which is a step in the right direction, but players will always know a person is lying if you're offering up clues.

5ekyu said:
Any failed ability check can yield a setback, after all.
This I believe yields a better result.
Whether the NPC is telling the truth or lying, any failed roll (behind the DM's screen against passive Insight) provides a complication/setback in the fiction.

 
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Iry

Villager
I use Passive Insight and adjust my description of what the NPC says based on that, sometimes mentioning more details to a specific player who has a really high Passive Insight. Then I leave it up to the players to decide, which may or may not include more intense grilling if they think the character is suspicious. I never mention if they are lying or not in absolute terms.
 

Iry

Villager
There appears to be some confusion, you agree with Elfcrusher but then in your example, you provided lying clues thereby treating the Insight skill as a detect lie check. I do understand that you took the "detect lie roll" behind the DM screen which is a step in the right direction, but players will always know a person is lying if you're offering up clues.
I don’t want to speak for Charlaquin, but those are indicators of the speaker feeling emotions. Not necessarily that they are lying.
 

Sadras

Explorer
I don’t want to speak for Charlaquin, but those are indicators of the speaker feeling emotions. Not necessarily that they are lying.
Charlaquin specifically states "when the NPC lies to a PC I roll". An observant player would notice this pattern is usually followed by lying indicators (upon failures). When it is the truth the DM does not roll. I dunno, I could be mistaken but to me that seems like a bit of a give away.
 

Iry

Villager
Charlaquin specifically states "when the NPC lies to a PC I roll". An observant player would notice this pattern is usually followed by lying indicators (upon failures). When it is the truth the DM does not roll. I dunno, I could be mistaken but to me that seems like a bit of a give away.
I assume the DM is rolling either way. Could be their Deception/Persuasion check, a Knowledge check, a Saving Throw, or even the Deception/Persuasion roll of a third party to see what this NPC believes.

But the bigger takeaway is that averting eyes and sweating is not a reliable indicator that someone is lying. :p
 

Bitbrain

Explorer
In my game, if the NPC is telling the truth and the PCs suspect that they are lying, then it is a DC 5 insight check.

Unless your character is paranoid, then the DC is increased to 15.
 

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