How much information should the defender have when deciding whether or not to cast Shield?

Question

I'm playing a 5e campaign as a Fighter, planning on becoming an Eldritch Knight.

Thus far (we're still level 1), the DM has been resolving attack rolls against us by telling us the result of the attack roll, and asking us if it hits:

• DM: "The goblin takes a swing at you!" (rolls behind DM screen) "Does a 19 hit you?"
• Player: (looks at character sheet) "Yep. Ouch!"

This has worked fine so far, since there isn't really anything any of our characters can do about being attacked, and you can't derive very much useful information from knowing what a monster's modified attack roll was. However, in a couple levels, I'm going to learn to cast spells, specifically the shield spell, which changes things a bit.

I know that I don't have to declare whether or not I cast shield until I know whether the attack would hit me, but am I supposed to know the exact modified attack roll result when I decide? Or should the sequence of events be more like:

• DM: "The goblin takes a swing at you!" (rolls behind DM screen) "What's your AC?"
• Player: (looks at character sheet) "It's 16."
• DM: "Okay, the attack hits."
• Player: "I cast shield in an attempt to protect myself, raising my AC to 21. Does it still hit me?"
• DM: "Nope, it glances off your magical barrier."

This is important because if I know the attack roll result, I know whether it's worth bothering to cast shield, whereas if it's hidden from me, I have to guess whether the attack beat my AC by 5 or more.

Answer 1

According to this tweet by Mike Mearls, you're supposed to know with certainty whether the shield is enough to protect you or not, so that you can't waste the spell, unless you choose to:

Querent: Am I right..Wiz should know roll before using Shield,cant 'waste it' from not knowing roll?

Mike Mearls: correct

This is also how I have seen it be done in every game I have played. The DM announces the attack score, and the player compares it to their AC and announces if it hits or not.

Answer 2

Whether it hits

Usually, the DM asks your AC before the play, and they take a note behind the screen. When they roll an attack behind the screen, they can immediately determine whether it hits or not. In this style, the DM only announces the hit, and not the total roll.

However,

your group has been using the other style: announcing the total attack roll.

It works with your group. Don't fix if it does not break.

You don't have to worry too much about "metagaming" the attack roll. What your player knows should be instinctively known to your character. If I'm the DM, if the roll can't be beat by Shield, I'll narrate the attack as a very fast attack, and you can't react fast enough to cast Shield, so you don't have to wonder whether to use shield or not. (Of course I tell them beforehand that was my intention: to speed up the encounter)

Alternatively,

discuss your plan to take Eldritch Knight and shield with your DM. Ask how they want to manage the usage of shield. Mention the different style (announcing only the hit) and whether they prefer that one over the current style. Let them choose, and stick with that one.

Again, don't worry about metagaming. If your DM don't worry about it, most likely you are worrying over a problem that doesn't exist.

Answer 3

There quite a few answers already covering why a DM might chose to not announce attack roll results, and how this is incompatible with having the Shield spell not be "wasted" sometimes. I'd like to show two practical approaches to solving this dilemma:

Announcing an "accuracy margin" along with the hit

Eg. instead of just saying "yup, the attack hits" I'd say "the attack narrowly hits" or "narrowly misses". I use the following table:

• Hit/miss by less than 5: "narrowly" hits or misses;
• Hit/miss between 5 and 10: no special wording - it just "hits" or "misses";
• Hit/miss by 10 or more: "soundly" hits or "wildly" misses.

This is the best of both worlds, I think. Besides allowing smarter uses of reaction abilities - you won't waste a Shield on an attack that soundly hit you - I found that this information actually helps player strategy and improves combat narration and realism. Players that notice that an strong but unskilled enemy does a lot of damage but often "barely" hits may use a full-defense action or other means to increase their AC; and they would be disinclined to do so if an enemy hits them "soundly" all the time, opting instead to just move away or disable such enemy.

Just have a Reflex roll

If a player, after being hit, declares an intention to use a reaction ability that may affect whatever the ability actually was a hit, I ask for a Reflex roll. If the roll succeeds, I tell the player if usage of such reaction ability will prevent the hit. If the roll fails, the player remains unsure. Regardless of the result, the player is not forced to use or not use the mentioned ability.

The roll has between Routine and High difficulty depending on the accuracy margins in question. For example, I'd say that knowing that an attack hit by a margin of 10 or more is a Routine task, while quickly discerning that an attack barely hit is a Hard task.

Those approaches have worked for me and my players before; and I specially like the first one. You may want to suggest that to your DM but - as usual - it'll be his call and if he's not very worried about your Shield spell, you probably shouldn't be either =).

Answer 4

If the OP is questioning whether the DM should reveal the roll, then the answer is, mostly no. Explained in the latter pages of the DMG, hidden rolls basically allow suspense and uncertainty. If you don’t trust your DM, then you need to have a talk with them. (See the "Dice Rolling" section on DMG pg. 235.)

The shield spell description states:

Until the start of your next turn, you have a +5 bonus to AC, including against the triggering attack, and you take no damage from magic missile.

As the spell states including the triggering attack, meaning when you confirm the attack as a hit, you then can choose to cast Shield as a reaction. RAW

You should know if the attack hits or not, any statistic ventures into the realm of metagaming. Now, a certain level of metagaming will happen, but is not a big issue if you leave that for OoC (Out of Character) times.

Take a moment to actually put yourself in the situation, a round is 6 seconds, as soon as you feel that weapon strike (that nanosecond the weapon would make physical contact, not just guessing it would) against your body, you mutter some words and wave your hand. Then POOF, you acted just in the nick of time to bring forth a barrier in hopes to block said strike.

If you know if the attack roll was too high enough to use the spell, then the spell is pointless. You are taking a chance to prevent yourself from injury or worse.

Answer 5

According to Jeremy Crawford, the player doesn't see the dice roll:

The shield spell has two different triggers: being hit by an attack or being targeted by the magic missile spell. Neither trigger requires you to see a die roll. #DnD

https://twitter.com/JeremyECrawford/status/972553916872183808