Are enemies' combat statistics and current HP public or hidden?

Question

During my very first game using D&D 5e as a DM where everyone has zero experience in TRPG, the party got in to a battle with 4 enemies. I was using Roll20 and I instinctively showed every player the enemies status and remaining health. After the session, I realized that I did not know how to handle enemies at all. My question is how much raw information do you reveal to the player? Do I...

1. Present the raw data to the player (the goblin has 15 HP, 7 AC. Your attack dealt 1 point of damage) or
2. Use descriptive term for everything and keep the number to myself? (the goblin looks weak and has a worn-out armor. Your attack barely scratch the goblin) ?

This also extend to the player as well. Should I allow the player to say "I have 7 HP left!" or should they only say "I'm almost down!" ?

Answer 1

Monsters' Hit Points

There is nothing wrong here if the DM decides to show actual Hit Points as numbers. See DMG, page 247:

Tracking Monster Hit Points
During a combat encounter, you need to track how much damage each monster takes. Most DMs track damage in secret so that their players don't know how many hit points a monster has remaining. Whether you choose to be secretive or not is up to you. What's important is that every monster's hit points be tracked individually.

If you decide to describe the HP loss instead, use the Player's Handbook, page 197:

Describing The Effects Of Damage
Dungeon Masters describe hit point loss in different ways. When your current hit point total is half or more of your hit point maximum. you typically show no signs of injury. When you drop below half your hit point maximum, you show signs of wear, such as cuts and bruises. An attack that reduces you to O hit points strikes you directly, leaving a bleeding injury or other trauma, or it simply knocks you unconscious.

Remember though that Hit Points are not Health. A creature with some Hit Points lost is not necessarily injured.

Monsters' stats

Talking about AC and other statistics, that generally depends on the character. Is this kind of creatures familiar to him/her? You also can call for the character's knowledge check, to see if he/she knows about this particular kind.

In the fight, GMs often give hints about To Hit and AC like "you've barely hit it". Nothing prevents you from revealing actual AC after a couple of hits (or right from the start, if you think it is necessary).

Answer 2

As a player and GM, I tend to prefer descriptive terms for combat effects rather than mechanics terms. This is kind of subjective, of course; I'm sure some players like to know how close to dead the bad guy is.

But I look at this from more of a "character's-eye view". The Player knows if she hit the enemy or not, "You hit! Roll damage!" And they roll the damage dice, so they know what they've done. But then I try to convert the number into a descriptive statement.

"Four points of damage? Your sword slams into his side, leaving a line of red that's slowly dripping down. The goblin staggers, but doesn't fall..."

The player ought to know how wounded they are, and you shouldn't prevent them from saying their remaining HP. But again, as a player, I prefer to say things like, "I'm wounded, but heal Bob first!" or "I'm gonna die! Healer?!?" rather than "I'm down by 10% of my hit points" or "I'm down to five HP!"

It just feels more interesting that way, more "game-ish" and less "number-crunching-ish."

The other thing I've done as a GM is when a climatic battle is about to end WAY too fast to be fun, I might give the bad guys a few extra HP. I don't do it often -- that's not fair -- but if the PCs are about to just destroy a bad guy in 1 round, I might let him stagger on for another round or two before he falls. If the PCs know the enemy's HP, that doesn't work. (If I do that, I also boost the XP awards. And I use this tactic rarely, and only when a swift end to a fight will reduce the fun of the game. This is GM cheating, so I try hard not to abuse it.)

Answer 3

Give the AC, but not the HP or saves

DMG 247 gives DMs wide latitude on what to reveal to players. This is an area where there's extraordinary variation between DMs. However, in my experience as a DM and a player, we have settled on giving only the AC. I'm also answering from a game table perspective, not an in-game perspective.

Players can usually figure out what the AC is

Players are frequently making attack rolls, which means they have a large sample size for determining AC (at least for any enemy that lasts a few rounds). For example, if the fighter misses on a 17, but the rogue hits on a 19, the players can quickly determine that the AC is at least 18. Given that this behavior is so routine, hiding the AC just adds a layer of unnecessary complication to the fight.

Reasons to hide HP and saves

The main reason to hide HP and saves is that they're never obvious to the players, which lets you keep the all-important fudge factor--if a boss is going down too quickly, or is going to die to a single spell, you can always add more HP or fudge the roll (the Legendary Resistance feature of some monsters codifies this).

The second is that some uncertainty is actually good. By giving general descriptors, players tend to be a bit more cautious and tactical in their play, which I think makes for a better game.

This is not a hard rule

If a fight is becoming a slog and we're getting bored, one of my DMs will give the HP of the remaining monsters to show how much progress we've made. Alternatively, the DM can say that we've dealt X damage but the monster is still fine, as a way to tell us that a monster is strong. You're the DM, and there's no rule that says you have to be consistent in what you give.

Players should be able to talk numbers

I think that you might be asking if the players should know how much damage they're dealing. This is a definite yes, because they should be rolling the damage dice.

Moreover, the players know the HP of their characters, and forcing the players to use descriptors instead of the numbers creates the same problem as hiding the AC--you're essentially forcing the players to create a code for a number rather than the number itself, which adds another unnecessary layer of complication.