Somehow I managed to run my last D&D campaign very successfully without really paying much thought to skills. And I can’t even really remember any specific instances where I had the players make skill checks. Surely we can’t have been playing for five months without any skill checks coming up, but with the way things played out, there wasn’t much need for them. For most interactions, the outcome happened to be obvious without a die roll needed. But going forward, and aiming for adventures with more ruin exploration and investigation of strange phenomenons, I think it will be useful to properly look at the skill and come up with a general ruling on when and how they are used in my next campaign.
When to call for checks
As a general rule of thumb, I like to go with the approach of “Assume Competence”. The PCs are adventurers, doing adventuring stuff for a living. They also are natives who have lived their entire lives in the setting of the campaign. If they encounter something that someone in their position would be likely to know, there’s no point in being shy about the information. Just tell the players what they are looking at, and the relevant context of what it means. Similarly, if an action is something that you wouldn’t think of being a problem, and the off chance of a possible failure wouldn’t carry big significant consequences, there is generally no point in calling for a check. As such, I think checks with a Difficulty Class of 10 (easy) are generally not worth rolling unless the PC in question has a really poor modifier, and DC 5 (very easy) checks only make any sense if the consequences of failure would be catastrophic. (I like making players deal with what fate has given them, and carry on forward in the face of defeat. Success in any venture is never guaranteed.)
How to roll checks
Another policy I’ve adopted in the past is that ability checks and skill checks are always called by the GM, never declared by the player (who then usually rolls a die without waiting for a response). I like to first talk through the whole situation and make sure the player has understood what’s going on, and I am clear on what the player is trying to accomplish. A die roll is almost always made to generate a randomized answer to a question. It’s important that we’re all on the same page what the question is first. And then, as the GM, it is me who decides which ability or skill applies to the attempted action. Something that I’ve not done yet, but absolutely plan to going forward, is to always declare the DC of the roll when calling for a check. This has three reasons.
The first thing is that it speeds up play a little bit. When a player shouts “I want to do X, and I’ve rolled a 16”, I need to take some time to think about what an 18 means in this situation. If a roll is a 2 or a 24, it’s obvious if that means success or failure. But a 13 or a 16? Deciding if the DC should be a 10 or a 15 retroactively after the player already announced the result is a situation I would refer to as sub-optimal. Now I’ve to make a judgement call I really don’t want to make in the first place. That puts me in a weird spot and takes time while the players wait for me to decide what to do. And with my ADD, I tend to get moments of brain lock in these situations and take even longer to sort out my thoughts what just happened and what I have to do now that the player announced a number.
The second reason is dramatic. If you declare the DC before the roll is made, all the player can stare at the dice to see how it lands, and if the player mentioned what the modifier is on the roll, they get the result immediately. The player does not have to tell me the result and I don’t need to come up with an eloquent way to describe the outcome. It’s already there for everyone to see.
And thirdly, it establishes that I as the GM am completely disinterested in the outcome of the skill check. The players propose an action, I tell them the DC. All the responsibility of what happens next lies exclusively with the players deciding to take the action and the roll of the dice. I am not influencing the outcome of their plan one way or another. (Though, of course, I still have a great degree of creative freedom of what a success or failure actually means specifically.) This is an essential component of actual open-ended sandbox play.
Strength (Athletics) is very straightforward. Make a judgement call on whether a physical task is medium, hard, very hard, and call for a roll on the corresponding DC. Failure while climbing means the character makes no progress that round. Failing by 5 or more means the character falls at the halfway point of that round’s movement.
Dexterity (Stealth) is checked once per “obstacle”. Any group of guards counts as a single obstacle, regardless of how many guards are in the group. Getting to the stairs while staying out of the lamp light is one obstacle, going up the creaking stairs without making noise is another obstacle, even through they could both be done in the same round. To hide in combat, the character first needs to break line of sight to any enemy you want to hide from (movement) and then conceal yourself in a hiding space while being observed (action). To attack from hiding, against an enemy who knows you’re somewhere nearby (because he just saw you run into the room or around the corner seconds ago) you need to be able to move from your hiding spot towards the enemy and make the attack in a single turn. Sneaking up on enemies who are currently in combat is impossible, unless you’re invisible or something close to it. Sneaking can be done as a group check. If at least half the members of the group get a Dexterity (Stealth) check that beats the Passive Perception of any guards or monsters, they are guiding the other characters with hand signals on when to move and where to step to also make it undetected successfully.
Intelligence (Arcana, History, Nature, and Religion) are usually passive skills. Assuming Competence, if something the players encounter would be known to all sufficiently educated people, they get the information for free as part of the initial description without specifically having to ask for it. The GM is the eyes and ears, and also setting knowledge of the PCs. These are things the players can’t really ask for unless they already know their significance. Skill checks can still be made in situation where players have a specific question about something they’ve been thinking of themselves.
Intelligence (Investigation) is always an active skill. An Intelligence (Investigation) check always serves to provide an answer to a question the player states to the GM. Figuratively speaking, a check is made when a player puts a magnifying glass to something the GM already described. The players still have to think by themselves to select an object for further investigation and ask a specific question about the object. “Can I find traces of poison?”, “Are there any signs of tempering on the metal?”, “Is it possible to estimate the person’s height based on the footprints?” Again, DC 5 and DC 10 checks are generally not worth making a roll and players get the answer simply for thinking to ask about it. Intelligence (Investigation) checks are made when only a trained expert could get an answer. The DC for the roll may be kept hidden from the players if it seems appropriate for the situation, but the check is still made openly. In that case, failure could mean either “it’s not there” or “you can’t see it”.
“I search the room.” It is possible for players to make an Intelligence (Investigation) check to search an area or a specific object, but only one check may be made for each area and object, and only a single discovery may be made that way. If the whole party searches together, it counts as Working Together, and a single check is made by the most skilled character at advantage. It’s best for players to first search an area “manually” by describing what they are looking for and where they are checking specifically, as they will automatically find anything that is hidden in a spot where they thought to look. An Intelligence (Investigation) check at the end of the search has the chance to reveal one more hidden object that their previous searching has missed. This is an application of the paradigm “You can not roll dice to avoid playing the game!” that still keeps the Investigation skill in the game and useful.
Wisdom (Insight) is used to judge an NPCs sincerity and earnestness. Players have to announce a suspicion and make an active skill check. The roll is made in the open by the player, but the DC is always hidden. Both a failed check and a genuinely sincere NPC result in the reply “You don’t sense any duplicity.”. A high roll gives greater confidence that the NPC is actually sincere, while a low roll means a great degree of uncertainty. It is up to the players to decide what to do with that information. Again, group checks can be made by all PCs present at the interaction. More than two people searching only decreases the amount of time it takes, but does not improve the odds of discovering something.
Wisdom (Perception) is usually done passive, but players can declare that they are actively scanning their surroundings for things that stand out or could be a threat. In situations where it matters, this counts as an action for each round. (While a single character making a Wisdom (Perception) check still has the same odds as Passive Perception, groups of characters all watching actively do improve their odds of one of them spotting something well hidden.)
Charisma (Deception) checks are called any time the GM thinks an NPC has reason to be suspicious and not take the PCs at their word immediately. The checks are made against an opposed Wisdom (Insight) check by the NPC.
Charisma (Persuasion) checks are made to win over NPCs who are hesitant about a course of action. It can not convince NPCs to do things that are directly against their own interest. If trying to convince someone of the truthfulness of your claim, the DC depends on how plausible your story is. If trying to persuade someone of a course of action that is in their interest, the DC depends on how great the price for the NPC will be. The NPCs Wisdom or Intelligence bonus might be added to the die roll if it seems appropriate, as smarter NPCs would be more likely to understand the necessity for certain decisions. For tricking NPCs into assuming an action is in their interest even though it is not, Charisma (Deception) checks are made.