When a player announces that they are doing something that carries with it the risk of meaningful failure (where failure would represent significant wasted time, lost resources or opportunities, or physical danger), such as striking an enemy with a sword, persuading a merchant to cut you a deal, or fighting against the mind-controlling spell that a Lich has cast, the GM will call for the character to make a skill check to determine whether they succeed. Below are the rules governing skill checks.
When the GM calls for a skill check, they should first ask the player for more information if needed. The GM should understand what success would look like to the player and what the nature of their plan for bringing that success about. If they do understand that, the GM determines the relevant attribute governing the skill check.
Fitness is the relevant attribute in skill checks who’s success depends most on the character’s strength and speed.
Dexterity is the relevant attribute in skill checks who’s success depends most on the character’s balance, precision, or ability to be undetected.
Charisma is the relevant attribute in skill checks who’s success depends most on the character’s persuasiveness or charm.
Learning is the relevant attribute in skill checks who’s success depends most on the character’s ability to recall trivia.
Awareness is the relevant attribute in skill checks who’s success depends most on the character’s ability to detect things with their senses which are not trivially detectable.
Though sometimes it will be ambiguous which attribute governs the skill check, mechanically only one attribute can govern a given skill check, and so the GM will have to decide.
After the GM determines the relevant attribute, the player is free to explain to the GM why one of their backgrounds is relevant to the skill check. A background is relevant when it implies that your character has some major life experience with the same type of activity that is involved in the skill check. Ultimately it is up to the GM whether or not the player’s background is relevant.
After this, the GM determines whether there is some special circumstance that gives the player advantage or disadvantage on the check. The most common factor that gives the player advantage is meaningful help from another player. Whether another player can meaningfully help depends on the circumstances of the check (some actions, such as getting out of the way of a trap or picking a lock, can’t easily benefit from another person’s help) and the helping character’s skill - if they have a 2 or higher in the relevant attribute or a relevant background they are qualified to help. Likewise the most common factor giving disadvantage is hinderance from a non-player character - this will often come up in conversations where a player’s attempt to persuade someone is stymied by an adversary’s attempt to prevent that same person from being persuaded. Other unusual circumstances can also grant advantage or disadvantage on a skill check.
Then, the player rolls their skill check. They roll 2d6, add their character’s score in the skill check’s relevant attribute, and if they have a relevant background they can also add their proficiency bonus. If they had advantage or disadvantage, instead of rolling 2d6, they roll 3d6, and count only 2 of the dice. If they had advantage, they count the 2 highest, and if they had disadvantage, the 2 lowest.
Advantage does not stack, and neither does disadvantage. If multiple effects would give a player advantage (or disadvantage), that still only roll 3d6. If both advantage and disadvantage are present for a check, they cancel each other out and the check is neither at advantage or disadvantage.
After rolling the skill check, the GM compares the player’s score to the difficulty class (DC) of the check - a number determined beforehand which expresses how difficult the task is. If the player’s score meets or exceeds that number, they succeed at what they were trying to do. If their score is lower than the DC, they fail.
Generally speaking, the easiest tasks worth calling for a skill check over have a DC of 6, and the hardest have a DC of 20.
SPENDING AN ADVENTURE POINT - When you would fail a skill check, you can spend 1 adventure point to re-roll one of your dice, possibly turning a failure into a success. You may only spend an adventure point in this way once per skill check.