Can you retroactively increase your Stealth roll while hiding?

Question

The rules for hiding (PHB 177) has an interesting clause, which makes it distinct from many other contests.

When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence.

Here we have a contest where you make a roll at one point in time, then at later points in time that roll's result is contested by another party's roll.

Is it possible for someone who is already hiding to increase their Dexterity (Stealth) check total without re-rolling their check? Possibly by application of guidance, pass without trace, Epic Boon of Fate, or a similar ability? Or is the check total immutable once the initial check has been made?

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For context, the original reason for asking this question was in response to this answer to "What is the highest total result one can get for a skill check?" where it was claimed that this special clause in the hiding rules would allow you to increase the check result on later turns without re-rolling using Epic Boon of Fate. However, this question is broader than just the Epic Boon of Fate.

Answer 1

There is no way to add to an already made ability check

Any feature that adds to an ability check will include some phrase such as "the next ability check the creature makes" or "when a creature makes an ability check" or something similar because these bonuses are added when the check is actually made, not afterwards.

The rules on ability checks state:

[...] To make an ability check, roll a d20 and add the relevant ability modifier. [...]

When the d20 is rolled, the check is made; after that point, the check has already been made and things cannot modify it unless they explicitly state that they can modify already-made checks.

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Stealth in particular states:

[...] Make a Dexterity (Stealth) check when you attempt to conceal yourself from enemies [...]

[...] When you try to hide, make a Dexterity (Stealth) check. Until you are discovered or you stop hiding, that check's total is contested by the Wisdom (Perception) check of any creature that actively searches for signs of your presence. [...]

None of this suggests that you can add to the check after it is made; the modifiers are applied when it is made and if you want to apply later modifiers then another check (a separate check) must be made.

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The guidance spell is perhaps an odd case as it's worded as follows:

[...] Once before the spell ends, the target can roll a d4 and add the number rolled to one ability check of its choice. It can roll the die before or after making the ability check. [...]

I, personally, wouldn't interpret this as being able to apply to checks made in the past. I don't have any proof that the intent of the spell is to add to a check when it is made, but if they had intended for it to be added at a different time, I feel it would have been worded more carefully and much more clearly.

Furthermore, the part of the description that might imply retroactive uses of guidance is "before or after" in which case we can use guidance after the check or before it. I honestly have no idea what adding 1d4 to a check you haven't even made would do and would use this as evidence to support my case that guidance can't be applied retroactively.

The "before or after" bit is meant to allow somebody to choose whether they want to add the d4 after seeing their roll and the result of that roll. Compare it with the Battle Master Fighter's Precision Attack Maneuver:

When you make a weapon attack roll against a creature, you can expend one superiority die to add it to the roll. You can use this maneuver before or after making the attack roll

Answer 2

Yes, you can modify an ability check result after the initial roll was made

As quoted by Medix2, the Player's Handbook does indeed say about ability checks:

To make an ability check, roll a d20 and add the relevant ability modifier.

It then goes on to say you should apply bonuses and penalties; however they are not part of the ability check itself. So if changing circumstances cause different modifiers to come into play, they can be applied to the base check for just as long as they are relevant. The check itself remains unchanged.

You give a couple of good examples of spells that can modify an ability check result in exactly this way.

The wording of the guidance spell explicitly talks of modifying a check after it is made:

[...] the target can roll a d4 and add the number rolled to one ability check of its choice. It can roll the die before or after making the ability check.

For example, my cleric can cast guidance on your rogue, who then takes the Hide action. Your rogue sneaks past a couple of goblin sentries using her Stealth check, but then notices a guard dog that she has to get past. She had been saving the guidance to apply its bonus to a difficult Athletics check to climb the wall behind the sentries, but she can now choose to add the bonus to her original Stealth check in the hope of staying hidden.

In the case of pass without trace, it can work the opposite way. At first your rogue benefits from the spell while hiding within 30 feet of my ranger who cast the spell, but when she strays further away, her Stealth check loses the +10 bonus. If she comes back within 30 feet, she gains the bonus again.

In an unofficial tweet from January 2016, Jeremy Crawford stated:

Pass without trace is meant to benefit you only while you're within the spell's radius.

So it is clearly his intention that an ability check result can be modified after the initial roll was made.

Answer 3

You misunderstand how Stealth checks work

Of course you can retroactively add to Stealth checks, like any other check with abilities that are in themselves retroactive (like, for example, how shield affects to-hit rolls). However, outside of such things, you can't increase a check total once it's made. Certainly there's no ability that lets you increase your total on a check the next round.

That's not what makes Stealth useful for Theoretical Optimization

You can't increase the total you made in the past, but you can increase your actual result in the future. The important misconception here is that you make one Stealth check while an opponent makes potentially hundreds of Perception checks. In actuality, you make one Stealth roll but many Stealth checks. This is required because:

Both participants in a contest make ability checks appropriate to their efforts

Since Stealth merely has you re-use the initial check's total rather than having you not make a new check, you can totally add to that initial total whenever you reuse it on a new check with anything that adds to checks in general, and nothing retroactive is occurring.

Far more ambiguous is what happens when you then make a third check: is your initial unmodified total used or the recent, higher total? After all, the rules for Stealth say "that check".

The key here is that your second Stealth check, reusing the first total, is also a Stealth check using the same rules. While no rule governs which of two totals you use to contest someone is actually used when there is more than one, that's irrelevant for both practical gaming and theoretical optimization for maximal Stealth checks, for the first case because the Stealth rules do not work as written and are routinely replaced by common sense and even in AL games this particular question doesn't matter since it is only relevant to the Boon of Fate and no player will ever have that and for the second because unambiguously the second check result is used for the third one in at least some sense, even if that sense may not actually have any meaning in game (e.g. if beating the lower of the two Stealth check totals allows a character to make you unbidden and all the other textual stretches necessary to make work arounds not work are also adopted).

Lastly note that that second question regarding Stealth check re-use past a second check only matters for epic boons. For any other ability, applying it a second time does nothing since the first total already includes it and all other bonuses to Stealth ability checks are game features and so don't self-stack. For maximizing effects like guidance, which involve a random component, if you get a bad ruling you just need to drop hiding before recasting the spell, which isn't a problem in situations where you are stealthing across multiple turns and have extra actions, and most DMs will make you drop hiding to cast a spell with verbal components anyhow.