[RPG] How to handle “I investigate for ” checks

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The characters enter a room, and get the general "what do you see" spiel.
One player announces that he wants to "Investigate the room for ". (Let's say "investigate for odd books") or the rogue says he stops the group at the threshold and wants to "investigate the room for traps or other danger".

I can see 3 main options for how I proceed from here:

  1. Treat everything after "I investigate …" as flavour fluff, ignore it, and treat it as an entirely generic "Investigate the room" check.
  2. Treat it as a very narrow investigation and only provide information that pertains to the specified target; the character can't notice anything that's not specifically related to the described investigation target, even if they, say, rolled a nat 20 and would otherwise have noticed the other suspicious things nearby.
  3. Do something along the lines of treating this as a general check but with some hindrance on general targets and some benefit to the specific targets. (Say +3 on the investigation of the books, but -3 on the investigation of the room as a whole.)

#1. Seems to ignore the players role-playing and agency.

#2. Is going to end up with the players having to list out everything that could be interesting and doing tonnes of Investigation checks.

#3. Feels like the most interesting and flavour-ful way to handle it, and rewards the players for correctly guessing what's suspicious. But is also clearly the furthest deviation from RAW.

What's the normal way to handle this?

Best Answer

Ask "How do you do that?"

Players do things by describing their actions. "I want to investigate the room for odd books" is not an action, it's a desirable goal. An action would be:

  • "I browse through every book on these shelves, until I find something like a spellbook"
  • "I start tapping the walls, trying to find a hiding place"
  • "I look under the bed. What do I see there?"
  • "I glance at the table. Do I see any odd-looking books there?"
  • ... other statement which gives insight about time, efforts and possible risks

Whilst describing a goal could be useful for determining the outcome, the general framework still states "players describe what they want to do", not "what they want to achieve". This is exactly how the rules describe the game process, see PHB page 6 "How To Play":

  1. The DM describes the environment.
  2. The players describe what they want to do.
  3. The DM narrates the results of the adventurers' actions.

"I investigate" is a valid action too, although it is very broad and vague. Adding "for X" doesn't make it clearer, unfortunately. When in doubt, a DM is free to ask for clarifications from players.

Don't rush with dice rolls

When players say they want to "investigate", that doesn't automatically mean they have to make an Intelligence (Investigation) check, or any kind of ability check at all.

What you're talking about is probably the "I use X skill" mentality, which came from previous versions (3.x primarily). It assumes that a player states the exact skill she is using, then she states the goal she wants to achieve, then a dice roll is necessary using the mentioned skill modifier:

"I want to disable this trap using my Disable Device skill!" (rolls the dice)

This is not how 5e works anymore. 5e has no skill checks for a reason. Instead, players describe their actions, then the DM describes the outcome. A DM doesn't have to ask for a dice roll. PHB suggests to roll dice only "where the outcome action is uncertain", and the DMG goes even further:

One approach is to use dice as rarely as possible. Some DMs use them only during combat, and determine success or failure as they like in other situations. With this approach, the DM decides whether an action or a plan succeeds or fails based on how well the players make their case, how thorough or creative they are, or other factors.

More specific example

So, let's say the party searches for an ancient grimoire. The party enters a room, then a player states "I want to investigate for odd books". What happens next depends on the multitude of factors. What do they do, exactly? What can be found here? Is there any time limit? Are we talking about a deliberate hiding place, or is the room just untidy? And so on:

  • If the room is a library, there're thousands of books here. "There are a lot of odd books here. How exactly are you going to find the proper one?" Maybe it's time to use the Locate Object spell, or ask NPCs, or do something else. Let your players be creative.
  • If it's an empty cell, there are no books at all. You don't want to waste time on pointless dice rolls. "You see no books here, just cold stone walls and a crude trestle bed". Maybe players would investigate the bed — again, describe it without rolls and move on.
  • A thorough search requires effort, but the party has plenty of time. On "How do you do that" they replied, "We leave no stone unturned until we find anything," so they will find all valuable things sooner or later, no dice roll is required. Just say what they did find. "You've spent a couple of hours and found an odd-looking spellbook and a sack of coins".
  • If it's a living room with many things and time is the essence, the outcome is uncertain. "Okay, you want to search for books here. How do you do that? You probably have only a couple of minutes before the orcs arrive." Perhaps the player will say, "Okay, I want to rummage through shelves as quickly as possible." The risks and reward are clear, so you ask the player for a roll. The result is quite high but you know the book isn't there. "Well, you can't see any books here, but you've found an intriguing letter signed by Black Spider." Or, on a failed check: "In a rush, you accidently drop one of the shelves on the floor. Boom! You bet someone could hear this."
  • Et cetera.

There can't be one "generic" answer, as there can't be a generic "Investigate the room" check in 5e.

Traps are a completely different topic

Speaking of traps, there is no silver bullet for them either. Moreover, making good traps is difficult, there are a lot of guides and videos on this topic. You can start with this one for example. Or watch this video.

Angry GM summarized the rolling part as "Only Roll When There is Chance of Success, A Chance of Failure, and A Risk or Cost of Failure" here (rule 2, hence Title Case). Being short and somewhat pithy helps me keep it in mind when GMing.

(kudos to @minnmass for the summary)

For instance, if you give players a chance to notice traps only when they explicitly say "I investigate the room for traps", they will probably say this in every room, and nobody will enjoy this. Instead, it might be a better option to use Passive Checks, or ask for a Wisdom (Perception) check right before the trap could spring.

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