If a feature has to be used before you know the result of an attack, what happens on a critical hit/miss?

Question

This is inspired by the recent question: "Can I use the Enchantment wizard's Instinctive Charm feature after seeing the die roll?" where this is mentioned at the end, but to avoid having multiple things going on there at once I thought it would be a good idea to ask this separately.

There are a few features in the game that occur "after seeing the roll, but before knowing whether it hits or misses", (or at similar times):

Valor Bard's Combat Inspiration:

[...] When an attack roll is made against the creature, it can use its reaction to roll the Bardic Inspiration die and add the number rolled to its AC against that attack, after seeing the roll but before knowing whether it hits or misses [...]

Enchantment Wizard's Instinctive Charm:

[...] When a creature you can see within 30 feet of you makes an attack roll against you, you can use your reaction to divert the attack, provided that another creature is within the attack's range. The attacker must make a Wisdom saving throw against your wizard spell save DC. On a failed save, the attacker must target the creature that is closest to it, not including you or itself. If multiple creatures are closest, the attacker chooses which one to target. On a successful save, you can't use this feature on the attacker again until you finish a long rest.

You must choose to use this feature before knowing whether the attack hits or misses [...]

Bard's Cutting Words:

[...] You learn how to use your wit to distract, confuse, and otherwise sap the confidence and competence of others. When a creature that you can see within 60 feet of you makes an attack roll, an ability check, or a damage roll, you can use your reaction to expend one of your uses of Bardic Inspiration, rolling a Bardic Inspiration die and subtracting the number rolled from the creature’s roll. You can choose to use this feature after the creature makes its roll, but before the DM determines whether the attack roll or ability check succeeds or fails, or before the creature deals its damage.

Conquest Paladin's Guided Strike:

You can use your Channel Divinity to strike with supernatural accuracy. When you make an attack roll, you can use your Channel Divinity to gain a +10 bonus to the roll. You make this choice after you see the roll, but before the DM says whether the attack hits or misses.

I would like answers here to assume that the player is told the actual number that appears on the die, this is supported in the in the following Q/A:

• Does Combat Inspiration require the GM to announce attack roll totals?
• How much does a bard know when they decide to use Cutting Words?

What I'm wondering is when using a feature like Combat Inspiration, what happens when the GM announces that the roll was a 1, or a 20? Does this mean you "know whether it hit or missed" and thus can't use the feature?

Answer 1

You can use the feature until the DM declares the result

The intent of this features is to be used between the rolling of the dice and the DM declaring the results. If there was meant to be special behaviour on a 20 or a 1 the features would say so.

Natural 20's can still miss

It is possible for there to be situations where a natural 20 is not a guarenteed hit. It happens when you are guessing the target's location, if the target has mirror image active, or any number other defensive abilities that can negate or redirect an atttack. They don't even need to be official as DM's could easily be running a homebrew monster that is the target for this situation.

Seeing a 20 on the dice does not mean that you "[know] whether the attack hits or misses" and you can therefore still use the ability.

It's mostly irrelevant

Almost all of these abilities in some may affect the modifiers to an attack roll. However the rules say:

If the d20 roll for an attack is a 20, the attack hits regardless of any modifiers or the target's AC. [...]

If the d20 roll for an attack is a 1, the attack misses regardless of any modifiers or the target's AC.

Due to this, the chance of someone wanting to use abilities like this on a 1 or 20 is highly unlikely. No amount of modifiers can affect the result anyway.

Answer 2

The rules for making an attack state:

If the d20 roll for an attack is a 20, the attack hits regardless of any modifiers or the target's AC. This is called a critical hit, which is explained later in this section.

If the d20 roll for an attack is a 1, the attack misses regardless of any modifiers or the target's AC.

So if a player is making the attack, a second (or the same, depending on the ability) player can't influence a critical hit or miss anyway. Beyond this, It's wise for the DM and player(s) to powwow and figure out how they want to handle the ability for concealed rolls (i.e. the DM's) and critical rolls that presume/require the player's ignorance.

In our group, the DM generally announces "high, low, or average" rolls, giving the player the option to react before the actual result is revealed. Narratively, this works out to the character having visual cues for how strong/accurate an attack seems that the player can't have at the table.

In the case of critical attacks, we just announce them outright. We don't want to make critical hits against players even more costly by potentially allowing players to waste defensive abilities on them, too.

But there are other solutions which can and must be used because the rules do not really provide a solution for these special exceptions.

Answer 3

You can still miss on a 20, and you can still hit on a 1*

Even if you see the 20 or 1, the attack isn't resolved and you cannot be 100% sure of the result. The rules state that a 20 or 1 only ignore AC and modifiers, not anything else:

If the d20 roll for an attack is a 20, the attack hits regardless of any modifiers or the target's AC.

If the d20 roll for an attack is a 1, the attack misses regardless of any modifiers or the target's AC.

There are other things besides AC and modifiers that can cause an attack to hit/miss.

One obvious example is that you can be forced to reroll die. Even if you roll a 1 or a 20, if you reroll the die then your miss or hit may not be a miss or hit anymore. This is clear proof that rolling a 1 or 20 isn't enough to say conclusively that you have missed or hit.

Another example is that you can miss on a 20 by guessing a target's location wrong:

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.

_{*I'm sure there are situations where it's possible to hit on a 1, but there's isn't anything in the rules that disallows it.}

Answer 4

If you roll a 1 or 20 on an attack roll, you know whether it hits or misses

Since a 1 always misses and a 20 is always a (critical) hit, if you see those numbers, the result is known. Therefore, you cannot use any ability that requires you not to know.