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

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:


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.


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