Does the Valor bard's Combat Inspiration feature require the GM to announce attack roll totals?

Question

I'm currently playing a 5E bard for the first time, and have chosen the College of Valor. The description of the Combat Inspiration feature reads (PHB, p. 55):

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.

In my time as DM I would always say, for example, "18 to hit?" unless it seemed absolutely clear to me that an attack hits. However, my current GM prefers to keep track of our AC, and simply tell us the result without calling the results of his attack rolls.

These are the possible solutions that occur to me:

• GM must consistently call '## to hit?' waiting for the player to respond 'Hits!' (Positive: Most useful for the inspired character. Negative: some immersion lost.) This is my preferred approach.
• GM must remember who has inspiration and at least announce his attack-rolls against them (Positive: best of both worlds. Negative: GM is likely to forget)
• GM does nothing; player must gamble on the use of their inspiration based on their own guess, intuition, or reading of the DM, and announce this immediately after the GM rolls attack. (Positive: Best for immersion, easiest for GM. Negative: the class feature becomes much less powerful. All of the onus is on the player to remember and interrupt the GM). I believe RAW rules out this solution, which is the one preferred by my GM.

Answer 1

The GM must reveal the number on the die

Whenever a player has an ability to do something after knowing "the roll, but not the result", the GM must either tell or show the player the number on the dice, as confirmed in this pair of unofficial tweets from June 2016 by rules designer Jeremy Crawford:

Bard Combat Inspiration use with reaction to add the roll to AC "AFTER SEEING THE ROLL" So DM must show his roll to player?

If a player character ability relies on knowing a monster's roll, a DM may say what the roll is or show it

Master @JeremyECrawford, you intended that DM must communicate only the number on the dice (without added any modifiers), right?

That's correct.

Relevant modifiers or target numbers do not have to be revealed, only the raw rolls of the dice.

Therefore, it is courteous and convenient for the GM to roll the dice openly whenever there is a chance for a player to use their inspiration, ask whether the player wants to use their inspiration, and declare the hit/miss after the player replies.

Answer 2

You must trust your DM quite a bit!

Which is good. I don't know that I could do the same, to be quite frank.

To answer the question, I think we're going to have to parse out the language, and I think the result will be something of a blend between your 2nd and 3rd bullets. I will hedge my bets here and say that this is an interpretation of this particular DM's method, so there very well may be a better answer.

The ability says "after seeing the roll", not "after seeing the result of the roll".

As such, the inspired PC only needs to know that they are being attacked. The DM has to give the inspired PC the opportunity to implement this mechanic, so s/he should give the PC an indication that one or more attacks have been made against them.

But, because your group has agreed to this particular method of attack rolls made by the DM, you're going to have to guess whether the DM's attack roll hit you by a bunch, or just by a couple. There's nothing that states specifically that you have to see the number on the die since the wording reads "before knowing whether the attack hits or misses."

You're going to want to clear this up with your DM sooner rather than later.

Especially considering there are other abilities, spells, and magic items that create a similar effect. Off the top of my head, the shield spell works much the same way (and that would be at the cost of a spell slot, so potentially a significant gamble).