When Perception contests Stealth, how do you know which side gets advantage or disadvantage?

Question

When we run skill contests, especially Stealth contested by Perception, we sometimes struggle to work out whether to apply advantage to one skill or disadvantage to the other. It matters for two reasons:

• multiple advantages and disadvantages don't stack for any single skill check
• advantage and disadvantage cancel each other out

An example may serve to illustrate:

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Example

The dwarven fighter became separated from the rest of the party and was stuck in a long dark tunnel with three human cultists bearing down on her; they were carrying lights but she was still in darkness. She made a Stealth check to hide from them because she wanted to shoot at them with advantage. Here's how I ruled advantage and disadvantage would stack up on the respective Stealth and Perception checks:

• The fighter's Stealth check had advantage owing to being heavily obscured in the darkness
• The fighter's Stealth check had advantage due to her boots of elvenkind
• The fighter's Stealth check had disadvantage due to her armour
• The fighter made a standard Stealth check because the advantage and disadvantage cancelled out; the second advantage did not come into play
• The cultists' Perception check had advantage because they had already been attacked by the fighter, they knew she was hiding in the darkness up ahead of them, and they expected further attacks to come from that direction.
• The net result was that a standard Stealth check was contested by an advantaged Perception check.

Reviewing the PHB rules on Light and Vision afterwards, I realised I should have made the heavy obscurement into a disadvantage for the cultists. That would have changed the skill contest as follows:

• The advantage to the fighter's Stealth check granted by being heavily obscured would have become a disadvantage to the cultists' Perception check.
• The fighter would still have made a standard Stealth check because she would still have had advantage and disadvantage, which would cancel out
• The cultists' Perception check would have had disadvantage because the fighter was heavily obscured from them
• The cultists would now have made a standard Perception check because their existing advantage would have been cancelled out by the new source of disadvantage
• The net result would then have been: a standard Stealth check was contested by a standard Perception check.

I'd given the cultists an unwarranted leg-up.

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So the question is, for the factors that affect the Stealth vs Perception skill contest, which do you apply to the Stealth check, and which do you apply to the Perception check?

Your reply should address some or all of the following factors, saying which check each applies to, and why:

• movement of the stealthing or perceiving creature
• obscurement
• cover
• camouflage
• attention or distraction of perceiving creature
• ambient light, noise or smell

Answer 1

This is not something that has a definitively right or wrong answer, however, the choice does have mechanical effects. Because disadvantage cancels any number of advantages (and vice-versa) piling them all on one roll or the other gives a different outcome than if you split them between the rolls.

For your example, the second is more right than the first but only because dim light specifically imposes disadvantage to Perception checks as it is a "lightly obscured" area (PHB p.183).

In general, when considering advantage/disadvantage situations consider who is advantaged or disadvantaged - the effect should apply to their roll or passive check.

For the situations in your example, this is how I think about it (which does not mean it is right or the way you or anyone else should think about it):

• Being heavily obscured - being unable to be seen (or seen clearly) is a prerequisite to hiding and provides neither advantage nor disadvantage to Stealth. It does, however, provide disadvantage on Perception (both lightly and heavily obscured do this)

• Boots of Elvenkind - gives advantage to Stealth because they say they do

• Heavy armor - gives disadvantage to Stealth because they say they do

• Knowledge of the Fighter's presence - to me, this doesn't suggest advantage: I've played hide and seek and knowing that there are people out there to find doesn't really make it easier to find them. Knowing that she is there allows the pursuers to spend an action to make an active Perception check rather than relying on their passive Perception - you get passive Perception for free but active Perception costs you. Remember, succeeding on a Perception check means you know exactly where the person is: it doesn't necessarily mean you can see them - you may have located them be smell, or hearing, or touch, or (in truly exception circumstances) taste - Invisible creatures can be Perceived!

  As an aside, if they are using their action to Dash rather than Search, this may warrant disadvantage on their passive Perception (and they can't make an active check) as they are hurrying by too swiftly to take proper stock of their surroundings. This gives pursuers a nice dilemma - if their quarry is hiding they want to go slower and look for them but if their quarry is running then they want to run too - you pay your money and you take your chances.

For me this gives a Stealth check with advantage cancelling disadvantage and a Perception check with disadvantage: either -5 on a passive check or roll twice take lowest on an active check and they only get their active check if they spend an action to Search.

Answer 2

Having given this some thought, and after reviewing the other answers, here's my take.

When advantage and disadvantage might apply to Stealth checks

• movement by a hiding creature - keeping still might grant advantage on its Stealth check, moving slowly might have no effect, moving at normal speed or faster might impose disadvantage.
• camouflage - normally grants advantage if it matches the environment.
• being inherently conspicuous - giving off or bearing light, or being or wearing something noisy will impose disadvantage or preclude you from being stealthy. Consider a cat wearing a bell, a cleric in full plate, or a commoner lighting her way with a candle.

When advantage and disadvantage might apply to Perception checks

• obscurement and cover from the perceiving creature - separately or in combination these may impose disadvantage, possibly with extra penalties. They apply to Perception checks because they are always relative to the perceiving creature, for example a hobgoblin in an area of dim light is lightly obscured from a human but not from a dwarf, owing to the dwarf's darkvision.
• movement of the perceiving creature - consider whether being still or moving fast affect Perception checks with advantage and disadvantage respectively.
• physical impediments to perception can affect senses such as hearing and smell. Consider the difference between a PC hiding behind a large wardrobe, or behind a closed door in the neighbouring room: one will be easier for a wolf to sniff out than the other. Watching or listening to a conversation is easier when you are in the same room rather than having to press your eye or ear to the keyhole of a door. Some sorts of obscurement might also acts as physical impediments: dense fog, thick vegetation and heavily falling snow can all mute sound and smell.
• attention and distraction might grant advantage or impose disadvantage respectively. An example of attention is seeing a goblin hide behind a tree, such that you are pretty certain you know where the goblin is. You are attending to the goblin's position, which makes it easier to find it again. This usage has been set out by both Jeremy Crawford and Mike Mearls (but they impose disadvantage on the Stealth check rather than advantage on the Perception check).

This discussion has crept beyond the original scope of the contest between Stealth and Perception - what with watching conversations through doors, and all - but I think the factors set out here still apply to these skills in isolation, as well as in contest.

Answer 3

It seems like you answered your own question. I could see resolving this in one of two ways.

Be more familiar with the rules

I'm not trying to sound rude, but all it came down to was that there were rules that you didn't remember. If it's important to you, possibly make a cheat sheet especially for Perception/Stealth to keep with you.

Roll all Perception/Stealth contests without Advantage/Disadvantage

(unless either side has a clear, uninhibited advantage/disadvantage.)

Each side of a contested roll is likely to have its own advantage(s) and disadvantage(s). However, there is a rule

If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.

Therefore, if you are ever in a situation where you are going through multiples, you could summarize it as saying both sides of both and therefore roll a single d20.

Answer 4

Modifiers for ability checks are with respect to each check.

Ability Checks

To make an ability check, roll a d20 and add the relevant ability modifier. As with other d20 rolls, apply bonuses and penalties, and compare the total to the DC.

Advantage and Disadvantage

Sometimes [...] you have advantage or disadvantage on an ability check [...]

You usually gain advantage or disadvantage through the use of special abilities, actions, or spells. Inspiration can also give a character advantage. The DM can also decide that circumstances influence a roll in one direction or the other and grant advantage or impose disadvantage as a result.

If multiple situations affect a roll and each one grants advantage or imposes disadvantage on it, you don't roll more than one additional d20. If two favorable situations grant advantage, for example, you still roll only one additional d20.

If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.

Special abilities, actions, spells and Inspiration are in the player’s domain. Some circumstances are called out in the rules, and some are ad-hoc, adjudicated by the DM.

A bonus or penalty applies to the ability check.

Contests are different, but modifiers still apply to each check.

Both participants in a contest make ability checks appropriate to their efforts. They apply all appropriate bonuses and penalties, but instead of comparing the total to a DC, they compare the totals of their two checks.

A penalty on one side, does not cancel out a bonus on the other side.

When we run skill contests, especially Stealth contested by Perception, we sometimes struggle to work out whether to apply advantage to one skill or disadvantage to the other.

For the modifiers defined by the rules, this is determined for you.

For ad-hoc adjustments, narratively, you should apply the modifier to the side that is the source of the modifier. If you determine an effect impacts the ability of one actor to perform a task, that should be advantage or disadvantage on that actor's ability check.

For example, if a rogue is trying to sneak passed talking guards, you might grant disadvantage to the guards' Wisdom (Perception) checks, since they are distracted by their conversation. However, if a cat pounces in front of the rogue from atop a wardrobe, you might impose disadvantage on the rogue's Dexterity (Stealth) check, as it might distract the rogue. If one of the guards leaves, you might grant advantage to the remaining guard, as she returns to vigilance.

For simplicity, let’s assume in your example that all enemies are aware of each other, the Order of Combat has been followed and this occurs during Step 4, Take turns. Since the cultists are carrying lights, let’s assume they do not have darkvision and the lights are torches, and the fighter has darkvision.

Other Adventuring Gear

Torch. A torch burns for 1 hour, providing bright light in a 20-foot radius and dim light for an additional 20 feet. If you make a melee attack with a burning torch and hit, it deals 1 fire damage.

- The fighter's Stealth check had advantage owing to being heavily obscured in the darkness

The fighter does not need to make a Stealth check to hide in a heavily obscured area.

The Environment

A heavily obscured area--such as darkness, opaque fog, or dense foliage--blocks vision entirely. A creature effectively suffers from the blinded condition when trying to see something in that area.

- The fighter's Stealth check had advantage due to her boots of elvenkind - The fighter's Stealth check had disadvantage due to her armour

Neither is relevant since no check is required.

- The cultists' Perception check had advantage because they had already been attacked by the fighter,

The cultists have no chance of seeing the fighter in a heavily obscured area. If on the fighter’s turn in initiative order, the cultists have ended their move within 60’, but outside of 40’, the fighter would get one round of being in a heavily obscured area, effectively invisible to the cultists, at which point the fighter could make an attack with advantage, with no ability checks being relevant.

However, once the cultists move within 40’ with their torches, the fighter would now be in a lightly obscured area (for the cultists). The fighter would need to take the Hide action, and would not be able to use the Attack action until the following round unless the fighter had some feature like a Rogue’s Cunning Action. Ideally, if there were previous rounds in which the fighter did not attack, the fighter would have already taken the Hide action. The cultists’ Perception checks are Passive, and have disadvantage.

If on the cultists’ turn, they move within 20’ of the fighter, then no checks are necessary as the fighter is now in bright light. The fighter could play cat and mouse, moving into darkness on each turn, but without a Rogue’s Cunning Action or similar ability, the fighter would not be able to attack, and the cultists could simply move within 20’ and attack normally.

Cunning Action

Starting at 2nd level, your quick thinking and agility allow you to move and act quickly. You can take a bonus action on each of your turns in combat. This action can be used only to take the Dash, Disengage, or Hide action.

Stealth

To determine whether such a creature notices you, the DM compares your Dexterity (Stealth) check with that creature's passive Wisdom (Perception) score, which equals 10 + the creature's Wisdom modifier, as well as any other bonuses or penalties. If the creature has advantage, add 5. For disadvantage, subtract 5.

Vision and Light

In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.

Bright light lets most creatures see normally.

In a lightly obscured area, the fighter’s check is normal, since that ability check has at least one source of advantage and at least one source of disadvantage. The rules-consequences of the fighter attacking the cultists is that the enemy would know the fighter’s location, however, that was prior to the fighter moving into darkness and does not apply until after the fighter attacks from darkness.

Unseen Attackers and Targets

When you attack a target that you can't see, you have disadvantage on the attack roll. This is true whether you're guessing the target's location or you're targeting a creature you can hear but not see. If the target isn't in the location you targeted, you automatically miss, but the DM typically just says that the attack missed, not whether you guessed the target's location correctly. When a creature can't see you, you have advantage on attack rolls against it. If you are hidden--both unseen and unheard--when you make an attack, you give away your location when the attack hits or misses.

- The cultists would now have made a standard Perception check because their existing advantage would have been cancelled out by the new source of disadvantage

- The net result would then have been: a standard Stealth check was contested by a standard Perception check.

I'd given the cultists an unwarranted leg-up.

The sources of advantage and disadvantage on a contested check are with respect to each check and should not have any bearing on the opposing check.

Bottom Line

When a bonus applies to one side, and a penalty applies to the other side, you might be tempted to cancel them out, but it would be a house rule that may significantly change the probability of the outcomes. Depending on the target DC, advantage or disadvantage can range from +/- 1 to 5, and be different for each opponent, depending on special abilities, ability scores and proficiency.

Further, the Lucky feat or a halfling's luck don’t get the commensurate benefit or detriment if you simply cancel out the sources of advantage or disadvantage on both sides.

Answer 5

In this specific case (perception against stealth) I would employ a very simple distinction: Anything advantage/disadvantage that would also apply to someone spotting a hidden object (stashed loot, secret door etc.) should go to perception. Anything that I would instead use to determine DC under those circumstances goes to stealth.