You will take many actions as an adventurer, each of which may end in success or failure.
Typically, the DM will only call for a dice roll if there is a possibility of success, a possibility of failure, and there are interesting consequences on both a success and a failure. For routine tasks performed without pressure or consequences, you can assume that a skilled character will succeed without needing to make a die roll. An unskilled character will automatically fail if the task is beyond their abilities; otherwise they will succeed after an appropriate period of time, provided there are no consequences for trying over and over again.
Let it Roll: As a narrative and gameplay device, once you have made a roll to determine the outcome of an action the results of that action stand. Typically you cannot try again at a task until the situation materially changes – if it was a task that could be repeated without consequence you should not have made a die roll to determine the result in the first place. The same applies on the success side: if you succeed at a task, you generally don’t need to make another die roll to keep the results active unless the situation materially changes. For example, if you successfully hide from a guard you won’t need to repeat that stealth roll until the situation materially changes.
Types of Activity Resolution
There are three main mechanics for determining the results of an activity: Attacks, Saves, and Checks.
Attacks
Attacks are offensive actions you take against an opponent. The most common example is a strike with a weapon, but attacks may also include spell attacks or using skills such as grappling to directly affect an opponent. Attacks are resisted by an opponent’s defense score (typically AC, but may be based on their saving throw modifiers or skill modifiers). Your chance of success with an attack depends heavily on the skill difference between you and your opponent. Therefore, attack modifiers and defenses both scale with level.
To determine whether you succeed with an attack, make an attack roll and compare the result against your target’s defense score. If the result of your attack roll equals or exceeds your target’s defense score, the attack succeeds and you apply the effects described in the activity block (most commonly, dealing damage.
Attack Roll: To make an attack roll, roll a d20 and add your attack bonus.
Attack Bonus = Proficiency Bonus + Modifier* + Character Level + Other Bonuses + Penalties
*For spell attack rolls and weapon attack rolls, your modifier is determined by your class. When using a Skill to make an attack, your modifier is the relevant ability score modifier for the skill (note: unlike Dungeons & Dragons, your ability modifiers do not influence your spell or weapon attack bonus).
Degrees of Success
Some attacks have scaling effects depending on your margin of success or failure. The ability block for these effects will be formatted as follows. Note that one or more of the following categories may be omitted. Use the highest category of success that applies. If you don’t meet any of the thresholds, use the “Failure” result. If the “Failure” result is omitted, then nothing happens on a failure.
Failure: apply this effect if none of the other options apply. Note: if the failure line is omitted from an activity block, it means “nothing happens” if none of the other options apply.
Failure (-5): applies if your result is 5 or less below the target’s defense score.
Success: applies if your result equals or exceeds the target’s defense score.
Success (+5): applies if your result is at least 5 higher than the target’s defense score.
Success (+10): Represents a critical success. Applies if your result is at least 10 higher than the target’s defense score.
Automatic Success Thresholds
When making an attack, a roll of 18 or higher on the d20 is a success (unless the result of the attack roll meets a higher threshold of success).
If the attack has a net circumstance bonus, the success threshold is instead 17 on the d20.
If the attack has a net circumstance penalty, the success threshold is instead 19 on the d20.
If the attack has a net circumstance penalty of -5 or greater, the success threshold is instead 20 on the d20.
(note: this rule was added to counterbalance the effects of removing bounded accuracy from the system. It guarantees that weak opponents will remain a minor threat against stronger opponents and also creates diminishing returns for improving defenses, all without having to tightly restrict the sources of bonuses and penalties available in the system)
Saves
Saves are defensive actions you take to resist an incoming attack or effect. Examples include diving for cover from a fireball and shaking off the influence of a vampire’s domination. The most common saves are Fortitude saves (influenced by your Strength modifier), Reflex saves (influenced by your Dexterity modifier), and Will saves (influenced by your Intelligence, Wisdom, or Charisma modifier). In special circumstances, you may instead be able to make saves using trained skills (for example, an Acrobatics save).
Succeeding at a save means scoring high enough on the result to overcome the difficulty threshold of the effect, represented by a Difficulty Class (DC) score. Your chance of success with a save depends heavily on the difference between your skill and the power level of the attack / effect. Therefore, save modifiers and DC’s both scale with level.
To determine whether you succeed in resisting an effect, make a saving throw and compare the result against the effect’s DC. If the result of your saving throw equals or exceeds the DC, you successfully resist the effect, as described in the effect’s activity block (most commonly, success reduces or eliminates the damage or status conditions that would be inflicted by the effect).
Saving Throw: To make a saving throw, roll a d20 and add your save bonus.
Save Bonus = Proficiency Bonus + Relevant Ability Modifier + Character Level + Other Bonuses + Penalties
Degrees of Success
Some saves have scaling effects depending on your margin of success or failure. The ability block for these effects will be formatted as follows. Note that one or more of the following categories may be omitted. Use the highest category of success that applies. If you don’t meet any of the thresholds, use the “Failure” result.
Failure: apply this effect if none of the other options apply.
Failure (-5): applies if your result is 5 or less below the DC.
Success: applies if your result equals or exceeds the DC.
Success (+5): applies if your result is at least 5 higher than the DC.
Success (+10): Represents a critical success. Applies if your result is at least 10 higher than the DC.
Automatic Success Thresholds
When making a saving throw, a roll of 18 or higher on the d20 is a success (unless the result of the saving throw meets a higher threshold of success).
If the attack has a net circumstance bonus, the success threshold is instead 17 on the d20.
If the attack has a net circumstance penalty, the success threshold is instead 19 on the d20.
If the attack has a net circumstance penalty of -5 or greater, the success threshold is instead 20 on the d20.
(note: this rule was added to counterbalance the effects of removing bounded accuracy from the system. It guarantees that weak opponents will remain a minor threat against stronger opponents and also creates diminishing returns for improving save DCs, all without having to tightly restrict the sources of bonuses and penalties available in the system)
Attack / Save Equivalency
Attacks and saves are reciprocals of each other. An attack roll can be thought of as the DC for a saving throw, and a saving throw can be thought of as the defense score for an attack roll. The only differences are automatic success thresholds and resolving ties (because of automatic success thresholds, an attack always has a chance to hit, but a saving throw doesn’t always have a chance to fail, and vice versa. Also, with an attack roll ties go to the attacker, and vice versa with a saving throw).
Sometimes it may be appropriate to convert an attack roll into a saving throw or vice versa. For example, say a wizard uses a pushing spell to try to move a boulder. The spell calls for the defender to make a Fortitude save to resist the push, but the DM may rule that it makes more sense to have the wizard make a roll to determine whether their spell is powerful enough, rather than having the rock roll a saving throw to resist being moved. In this case, the wizard should make a “potency attack”, using their spell DC – 10 as the attack modifier. The DM can then set an appropriate defense score for the rock to represent its resistance to being moved (note: because of the difference in resolving ties, the DM should consider increasing the target’s defense score by 1 to maintain equivalent odds of success).
Skill Checks
Skill checks are actions you take to solve a problem or overcome an obstacle that aren’t directly resisted by an opponent. Examples include picking a lock, climbing a wall, or identifying magical runes. Succeeding at a skill check means you achieve your objective. Your chance of success with a skill check depends on your talent and training, and the difficulty of the task. Because skill check difficulty represents a static obstacle rather than a skilled opponent, skill check bonuses scale more slowly than attack rolls or saves. You do not add your level to skill checks.
To determine whether you succeed in resisting an effect, make a skill check and compare the result against the task’s Difficulty Class (DC). If the result of your skill check equals or exceeds the DC, you successfully accomplish the task, as determined by the DM.
Depending on your expertise and the specialization of the task there are three types of skill checks available for resolving tasks, each with different probability distributions. The specialization level of a task determines the highest variability level allowed for the task. Low specialization skills (like a running jump) are high variability, while skills requiring high levels of technical expertise (like picking a lock) are low variability. The DM decides the maximum level of variability available for a given skill check. If you are highly trained in a task, you can elect to reduce the variability when making a skill check. If your proficiency bonus is at least +4, you can reduce the variability to Medium. If your proficiency bonus is at least +6, you can reduce the variability to Low.
Skill Check: To make a skill check, roll one of the following:
High variability: 1d20 + skill bonus.
Medium variability: 2d10 + skill bonus.
Low variability: 3d6 + skill bonus.
Skill Bonus = Greater of
[Proficiency Bonus + (Relevant Ability Score – 10) –or–
2x Proficiency Bonus + Relevant Ability Modifier]
+ Other Bonuses + Penalties
For example, a fighter is trying to climb a rope. He has a lot of strength, but relatively little training in this task. His proficiency bonus is +2 and his Strength score is 16. His skill bonus for this task is +8 (+2 proficiency, + (16 – 10 = 6) Strength). A rogue is also trying to climb the same rope. She is highly trained, but doesn’t have the same muscle the fighter does. Her proficiency bonus is +4 and her Strength score is 12 (for a +1 modifier). Her skill bonus for this task is +9 (2x (+4 proficiency), +1 Strength modifier).
Degrees of Success
Some skill checks have scaling effects depending on your margin of success or failure. The skill block for these effects will be formatted as follows (or the DM may create similar gradations for improvised tasks). Note that one or more of the following categories may be omitted. Use the highest category of success that applies. If you don’t meet any of the thresholds, use the “Failure” result.
Failure: apply this effect if none of the other options apply.
Failure (-5): applies if your result is 5 or less below the DC.
Success: applies if your result equals or exceeds the DC.
Success (+5): applies if your result is at least 5 higher than the DC.
Success (+10): Represents a critical success. Applies if your result is at least 10 higher than the DC.
Automatic Success Thresholds
Skill checks do not have automatic success thresholds. If you don’t have the skills necessary to have a chance accomplish a task, you don’t get to make a skill check.