Should RAW roll DC be known before roll?

Question

I'd like to know if GM is bound by rules to provide us with DC's we're supposed to roll against, before rolls. I'm specifically interested in:

• Skill Check DC's,
• Ability Check DC's,
• Save DC's,
• Caster Level DC's.

Answer 1

TLDR

It's a style choice of the GM, but generally often there's good reasons not to tell the DCs.

From the Rule Books

The rules are silent when they define the term DC

Difficulty Class (DC): Whenever a creature attempts to perform an action whose success is not guaranteed, he must make some sort of check (usually a skill check). The result of that check must meet or exceed the Difficulty Class of the action that the creature is attempting to perform in order for the action to be successful.

And the description of the Attack Roll doesn't list it either:

Attack Roll Source PRPG Core Rulebook pg. 178 An attack roll represents your attempt to strike your opponent on your turn in a round. When you make an attack roll, you roll a d20 and add your attack bonus. (Other modifiers may also apply to this roll.) If your result equals or beats the target’s Armor Class, you hit and deal damage.

The GM section in the core rules is also silent in During the Game, but the GameMastery Guide does point out that not all things are to be known to the players, especially if outcomes shouldn't be known for some reasons - such as rolling to find traps. In other cases it is up to the GM to give information or not - such as the attack rolls of the NPCs and opponents. The GM section seems to advocate to roll many things secretly to better allow fudging the game if needed and to keep up mysteries.

Running the game

Dice Rolling: Some dice rolls need to be made in secret, such as when a rogue looks for a trap or a monster attempts a Perception check. At other times, you may want to roll in front of the players, such as when a pivotal save is being made during combat which could potentially kill a player character. Making rolls in the open adds a sense of drama and fairness to the moment, and your players can see the result as they root for the outcome they desire. Yet doing so can also tie your hands unnecessarily, interrupt the flow of the narrative, and generally detract from the sense of mystery. For this reason, physical barriers like the Pathfinder RPG GM Screen come in handy.

GM Subterfuge: You don’t want your players to know when something important is happening by watching for you to roll your dice. As such, many GMs roll dice unnecessarily every so often, pretending to look something up in their notes. This makes it harder for players to guess when something significant has happened, such as a failed Perception check. It’s equally important for things like finding secret doors—if you don’t call for a Perception check simply because there’s nothing to see, the PCs quickly learn that rolling dice means something is up, whether they made their roll or not.

However, the best pointer to how to handle AC and other DCs for rolls might be in the section on Player Knowledge

Separating the information a player knows from the facts a character possesses regularly proves one of the most difficult challenges players face. “Metagaming,” or making decisions based on player knowledge as opposed to character knowledge, quickly erodes the group’s belief in the world the GM creates. It often frustrates both the GM and other players when an interesting adventure cracks because a given PC acts on information the character has no way of possessing, and such issues should be dealt with quickly and calmly when they come up.

Conclusions from the GM sections

The GM is told to keep information from the players whenever it serves their goals and is allowed to manipulate rolls as needed. That path of argument not only extends to rolling in secret as the GM, but it also advocates to not tell the players the DCs on for example rolls to detect the hidden door or treasure.

However, the same rules also allow the GM to give the player information, if it is in the interest of the game, or matches the style of the GM. The most relevant point here is that giving information on DC allows us to handle some rolls faster as it outsources the "you succeded" and can speed combat and reduce decision paralysis about which type of attack might succeed more easily. However, that does go directly contrary to the call for the GM to keep Metagaming in check.

The best way to prevent Metagaming, according to the section pointed to above, is to prevent the usage of such Meta-information in the first place. That would be the biggest argument for generally not giving the DCs of tasks. However, I also know that there are player types that you can handle knowing things as a player and not using them. But that requires a group that does like that kind of style and can handle it.

As a GM in Pathfinder I have often run the secrecy route:

• In combat, ACs and the DCs for spells for monsters were not given by me. The players told me their sum of roll plus modifiers, I told them if it hit or succeeded. If the players figured it out the AC or DC by having a hit and a miss right next to one another, so be it, and I accepted them to know that stat for this monster for the rest of the combat.
  • Knowing the AC/DC can speed up combat from my experience, but it also takes away any surprise. It's mostly something for repeat encounters with a type of monster.
• When players asked about the difficulty of specific tasks, I informed them in vague terms without revealing the actual DC. "How hard is it to climb that wall?" "It's smoothed with magic and without cracks, your character knows that it will be hard."
• I rolled dice for no reason other than rolling dice and asked whoever entered a room to roll a perception roll, even if there was nothing to be seen or the DC was trivial (1), just to mask those rolls that actually had impact.

Answer 2

No.

The presence of abilities like inspiration, which can be used for skill checks, ability checks, and saves, or the Luck Blade, which can be used for any roll, show that no, DCs are not public knowledge. Respectively:

[...] As a free action, he can expend one use of inspiration from his pool to add 1d6 to the result of that check, including any on which he takes 10 or 20. This choice is made after the check is rolled and before the results are revealed. [...]

[...] This extraordinary ability allows its possessor to reroll one roll that she just made, before the results are revealed. She must take the result of the reroll, even if it’s worse than the original roll. [...]

If the DCs are known, there's no meaningful time in which you have rolled the check but don't know the result of the check (in terms of passing and failing). This means that, by default, those DCs must not be known.

Answer 3

No.

This might be addressed directly somewhere in the Core Rulebook, and I will look for that, but it also might not: it may be the case that nothing directly discusses this.

But whether or not the rules directly confirm that the GM can or should keep DCs hidden, I am absolutely certain nothing directs the GM not to, or indicates any responsibility to reveal them in general (special cases may exist, such as positive information gathering by the players via Knowledge, divination, trial and error, etc). The absence of any such directive, of course, means the GM is free to keep that information hidden. I have played in games that did reveal that information, but that is unusual.