Ready to play? Build unlimited Pathfinder 2e characters Create Now

Before exploring the specific rules of each mode of play, you'll want to understand a number of general rules of the game. To one degree or another, these rules are used in every mode of play.

Making Choices

Pathfinder is a game where your choices determine the story's direction. Throughout the game, the GM describes what's happening in the world and then asks the players, “So what do you do?” Exactly what you choose to do, and how the GM responds to those choices, builds a unique story experience. Every game is different, because you'll rarely, if ever, make the same decisions as another group of players. This is true for the GM as well—two GMs running the exact same adventure will put different emphasis and flourishes on the way they present each scenario and encounter.

Often, your choices have no immediate risk or consequences. If you're traveling along a forest path and come across a fork in the trail, the GM will ask, “Which way do you go?” You might choose to take the right fork or the left. You could also choose to leave the trail, or just go back to town. Once your choice is made, the GM tells you what happens next. Down the line, that choice may impact what you encounter later in the game, but in many cases nothing dangerous happens immediately.

But sometimes what happens as a result of your choices is less than certain. In those cases, you'll attempt a check.

Game Conventions

Pathfinder has many specific rules, but you'll also want to keep these general guidelines in mind when playing. 

The GM Has the Final Say

If you're ever uncertain how to apply a rule, the GM decides. Of course, Pathfinder is a game, so when adjudicating the rules, the GM is encouraged to listen to everyone 's point of view and make a decision that is both fair and fun. 

Specific Overrides General

A core principle of Pathfinder is that specific rules override general ones. If two rules conflict, the more specific one takes precedence. If there's still ambiguity, the GM determines which rule to use. For example, the rules state that when attacking a concealed creature, you must attempt a DC 5 flat check to determine if you hit. Flat checks don't benefit from modifiers, bonuses, or penalties, but an ability that's specifically designed to overcome concealment might override and alter this. If a rule doesn't specify otherwise, default to the general rules presented in this chapter. While some special rules may also state the normal rules to provide context, you should always default to the normal rules even if effects don't specifically say to.

Rounding

You may need to calculate a fraction of a value, like halving damage. Always round down unless otherwise specified. For example, if a spell deals 7 damage and a creature takes half damage from it, that creature takes 3 damage.

Multiplying

When more than one effect would multiply the same number, don't multiply more than once. Instead, combine all the multipliers into a single multiplier, with each multiple after the first adding 1 less than its value. For instance, if one ability doubled the duration of one of your spells and another one doubled the duration of the same spell, you would triple the duration, not quadruple it. 

Duplicate Effects

When you're affected by the same thing multiple times, only one instance applies, using the higher level of the effects, or the newer effect if the two are the same level. For example, if you were using mage armor and then cast it again, you'd still benefit from only one casting of that spell. Casting a spell again on the same target might get you a better duration or effect if it were cast at a higher level the second time, but otherwise doing so gives you no advantage.

Ambiguous Rules

Sometimes a rule could be interpreted multiple ways. If one version is too good to be true, it probably is. If a rule seems to have wording with problematic repercussions or doesn't work as intended, work with your group to find a good solution, rather than just playing with the rule as printed.

Checks

When success isn't certain—whether you're swinging a sword at a foul beast, attempting to leap across a chasm, or straining to remember the name of the earl's second cousin at a soiree—you'll attempt a check. Pathfinder has many types of checks, from skill checks to attack rolls to saving throws, but they all follow these basic steps. 

1. Roll a d20 and identify the modifiers, bonuses, and penalties that apply.
   
2. Calculate the result.
   
3. Compare the result to the difficulty class (DC).
   
4. Determine the degree of success and the effect.
   

Checks and difficulty classes (DC) both come in many forms. When you swing your sword at that foul beast, you'll make an attack roll against its Armor Class, which is the DC to hit another creature. If you are leaping across that chasm, you'll attempt an Athletics skill check with a DC based on the distance you are trying to jump. When calling to mind the name of the earl's second cousin, you attempt a check to Recall Knowledge. You might use either the Society skill or a Lore skill you have that 's relevant to the task, and the DC depends on how common the knowledge of the cousin's name might be, or how many drinks your character had when they were introduced to the cousin the night before.

No matter the details, for any check you must roll the d20 and achieve a result equal to or greater than the DC to succeed. Each of these steps is explained below. 

Step 1: Roll D20 and Identify The Modifiers, Bonuses, and Penalties That Apply

Start by rolling your d20. You'll then identify all the relevant modifiers, bonuses, and penalties that apply to the roll. A modifier can be either positive or negative, but a bonus is always positive, and a penalty is always negative. The sum of all the modifiers, bonuses, and penalties you apply to the d20 roll is called your total modifier for that statistic.

Nearly all checks allow you to add an ability modifier to the roll. An ability modifier represents your raw capabilities and is derived from an ability score. Exactly which ability modifier you use is determined by what you're trying to accomplish. Usually a sword swing applies your Strength modifier, whereas remembering the name of the earl's cousin uses your Intelligence modifier.

When attempting a check that involves something you have some training in, you will also add your proficiency bonus. This bonus depends on your proficiency rank: untrained, trained, expert, master, or legendary. If you're untrained, your bonus is +0—you must rely on raw talent and any bonuses from the situation. Otherwise, the bonus equals your character's level plus a certain amount depending on your rank. If your proficiency rank is trained, this bonus is equal to your level + 2, and higher proficiency ranks further increase the amount you add to your level.

Proficiency Rank	Proficiency Bonus
Untrained	0
Trained	Your level + 2
Expert	Your level + 4
Master	Your level + 6
Legendary	Your level +8

There are three other types of bonus that frequently appear: circumstance bonuses, item bonuses, and status bonuses. If you have different types of bonus that would apply to the same roll, you'll add them all. But if you have multiple bonuses of the same type, you can use only the highest bonus on a given roll—in other words, they don't “stack.” For instance, if you have both a proficiency bonus and an item bonus, you add both to your d20 result, but if you have two item bonuses that could apply to the same check, you add only the higher of the two.

Circumstance bonuses typically involve the situation you find yourself in when attempting a check. For instance, using Raise a Shield with a buckler grants you a +1 circumstance bonus to AC. Being behind cover grants you a +2 circumstance bonus to AC. If you are both behind cover and Raising a Shield, you gain only the +2 circumstance bonus for cover, since they're the same type and the bonus from cover is higher. 

Item bonuses are granted by some item that you are wearing or using, either mundane or magical. For example, armor gives you an item bonus to AC, while expanded alchemist's tools grant you an item bonus to Crafting checks when making alchemical items.

Status bonuses typically come from spells, other magical effects, or something applying a helpful, often temporary, condition to you. For instance, the 3rd-level heroism spell grants a +1 status bonus to attack rolls, Perception checks, saving throws, and skill checks. If you were under the effect of heroism and someone cast the bless spell, which also grants a +1 status bonus on attacks, your attack rolls would gain only a +1 status bonus, since both spells grant a +1 status bonus to those rolls, and you only take the highest status bonus.

Penalties work very much like bonuses. You can have circumstance penalties, status penalties, and sometimes even item penalties. Like bonuses of the same type, you take only the worst all of various penalties of a given type. However, you can apply both a bonus and a penalty of the same type on a single roll. For example, if you had a +1 status bonus from a heroism spell but a –2 status penalty from the sickened condition, you'd apply them both to your roll—so heroism still helps even though you're feeling unwell.

Unlike bonuses, penalties can also be untyped, in which case they won't be classified as “circumstance,” “item,” or “status.” Unlike other penalties, you always add all your untyped penalties together rather than simply taking the worst one. For instance, when you use attack actions, you incur a multiple attack penalty on each attack you make on your turn after the first attack, and when you attack a target that's beyond your weapon's normal range increment, you incur a range penalty on the attack. Because these are both untyped penalties, if you make multiple attacks at a faraway target, you'd apply both the multiple attack penalty and the range penalty to your roll.

Once you've identified all your various modifiers, bonuses, and penalties, you move on to the next step.

Step 2: Calculate the Result

This step is simple. Add up all the various modifiers, bonuses, and penalties you identified in Step 1—this is your total modifier. Next add that to the number that came up on your d20 roll. This total is your check result.

Step 3: Compare the Result to the DC

This step can be simple, or it can create suspense. Sometimes you'll know the Difficulty Class (DC) of your check. In these cases, if your result is equal to or greater than the DC, you succeed! If your roll anything less than the DC, you fail.

Other times, you might not know the DC right away. Swimming across a river would require an Athletics check, but it doesn't have a specified DC—so how will you know if you succeed or fail? You call out your result to the GM and they will let you know if it is a success, failure, or otherwise. While you might learn the exact DC through trial and error, DCs sometimes change, so asking the GM whether a check is successful is the best way to determine whether or not you have met or exceeded the DC.

Calculating DCs

Whenever you attempt a check, you compare your result against a DC. When someone or something else attempts a check against you, rather than both forces rolling against one another, the GM (or player, if the opponent is another PC) compares their result to a fixed DC based on your relevant statistic. Your DC for a given statistic is 10 + the total modifier for that statistic. 

Step 4: Determine the Degree of Success and Effect

Many times, it's important to determine not only if you succeed or fail, but also how spectacularly you succeed or fail. Exceptional results—either good or bad—can cause you to critically succeed at or critically fail a check. 

You critically succeed at a check when the check's result meets or exceeds the DC by 10 or more. If the check is an attack roll, this is sometimes called a critical hit. You can also critically fail a check. The rules for critical failure—sometimes called a fumble—are the same as those for a critical success, but in the other direction: if you fail a check by 10 or more, that's a critical failure.

If you rolled a 20 on the die (a “natural 20”), your result is one degree of success better than it would be by numbers alone. If you roll a 1 on the d20 (a “natural 1”), your result is one degree worse. This means that a natural 20 usually results in a critical success and natural 1 usually results in a critical failure. However, if you were going up against a very high DC, you might get only a success with a natural 20, or even a failure if 20 plus your total modifier is 10 or more below the DC. Likewise, if your modifier for a statistic is so high that adding it to a 1 from your d20 roll exceeds the DC by 10 or more, you can succeed even if you roll a natural 1! If a feat, magic item, spell, or other effect does not list a critical success or critical failure, treat is as an ordinary success or failure instead.

Some other abilities can change the degree of success for rolls you get. When resolving the effect of an ability that changes your degree of success, always apply the adjustment from a natural 20 or natural 1 before anything else.

Calculating Check Results

If you have more than one bonus or penalty of a particular type, apply only the highest

Number on the die + Ability modifier + Proficiency bonus, Circumstance bonus, Status bonus, Item bonus + Circumstance penalty, Status penalty, Item penalty, All untyped penalties = Result

Specific Checks

While most checks follow these basic rules, it's useful to know about a few specific types of checks, how they're used, and how they differ from one another. 

Striding and Striking 

Two of the simplest and most common actions you'll use in combat are Stride and Strike.

Stride is an action that has the move trait and that allows you to move a number of feet up to your Speed. You'll often need to Stride multiple times to reach a foe who's far away or to run from danger! Move actions can often trigger reactions or free actions. However, unlike other actions, a move action can trigger reactions not only when you first use the action, but also for every 5 feet you move during that action. The Step action lets you move without triggering reactions, but only 5 feet.

Strike is an action that has the attack trait and that allows you to attack with a weapon you're wielding or an unarmed attack (such as a fist).

If you're using a melee weapon or unarmed attack, your target must be within your reach; if you're attacking with a ranged weapon, your target must be within range. Your reach is how far you can physically extend a part of your body to make an unarmed attack, or the farthest distance you can reach with a melee weapon. This is typically 5 feet, but special weapons and larger creatures have longer reaches. Your range is how far away you can attack with a ranged weapon or with some types of magical attacks. Different weapons and magical attacks have different maximum ranges, and ranged weapons get less effective as you exceed their range increments.

Striking multiple times in a turn has diminishing returns. The multiple attack penalty applies to each attack after the first, whether those attacks are Strikes, special attacks like the Grapple action of the Athletics skill, or spell attack rolls.

Attack Rolls

When you use a Strike action or make a spell attack, you attempt a check called an attack roll. Attack rolls take a variety of forms and are often highly variable based on the weapon you are using for the attack, but there are three main types: melee attack rolls, ranged attack rolls, and spell attack rolls. Spell attack rolls work a little bit differently, so they are explained separately. 

Melee attack rolls use Strength as their ability modifier by default. If you're using a weapon or attack with the finesse trait, then you can use your Dexterity modifier instead. 

Melee attack roll result = d20 roll + Strength modifier (or optionally Dexterity modifier for a finesse weapon) + proficiency bonus + other bonuses + penalties

Ranged attack rolls use Dexterity as their ability modifier. 

Ranged attack roll result = d20 roll + Dexterity modifier + proficiency bonus + other bonuses + penalties

When attacking with a weapon, whether melee or ranged, you add your proficiency bonus for the weapon you're using. Your class determines your proficiency rank for various weapons. Sometimes, you'll have different proficiency ranks for different weapons. For instance, at 5th level, a fighter gains the weapon mastery class feature, which grants master proficiency with the simple and martial weapons of one weapon group, expert proficiency with advanced weapons of that group and other simple and martial weapons, and trained proficiency in all other advanced weapons. 

The bonuses you might apply to attack rolls can come from a variety of sources. Circumstance bonuses can come from the aid of an ally or a beneficial situation. Status bonuses are typically granted by spells and other magical aids. The item bonus to attack rolls comes from magic weapons—notably, a weapon's potency rune. 

Penalties to attack rolls come from situations and effects as well. Circumstance penalties come from risky tactics or detrimental circumstances, status penalties come from spells and magic working against you, and item penalties occur when you use a shoddy item. When making attack rolls, two main types of untyped penalties are likely to apply. The first is the multiple attack penalty, and the second is the range penalty. The first applies anytime you make more than one attack action during the course of your turn, and the other applies only with ranged or thrown weapons. Both are described below. 

Multiple Attack Penalty

The more attacks you make beyond your first in a single turn, the less accurate you become, represented by the multiple attack penalty. The second time you use an attack action during your turn, you take a –5 penalty to your attack roll. The third time you attack, and on any subsequent attacks, you take a –10 penalty to your attack roll. Every check that has the attack trait counts toward your multiple attack penalty, including Strikes, spell attack rolls, certain skill actions like Shove, and many others. 

Some weapons and abilities reduce multiple attack penalties, such as agile weapons, which reduce these penalties to –4 on the second attack or –8 on further attacks.

Attack	Multiple Attack Penalty	Agile
First	None	None
Second	–5	–4
Third or subsequent	–10	–8

Always calculate your multiple attack penalty for the weapon you're using on that attack. For example, let's say you're wielding a longsword in one hand and a shortsword (which has the agile trait) in your other hand, and you are going to make three Strikes with these weapons during the course of your turn. The first Strike you make during your turn has no penalty, no matter what weapon you are using. The second Strike will take either a –5 penalty if you use the longsword or a –4 penalty if you use the shortsword. Just like the second attack, the penalty for your third attack is based on which weapon you're using for that particular Strike. It would be a –10 penalty with the longsword and a –8 penalty with the shortsword, no matter what weapon you used for your previous Strikes. 

The multiple attack penalty applies only during your turn, so you don't have to keep track of it if you can perform an Attack of Opportunity or a similar reaction that lets you make a Strike on someone else's turn.

Range Penalty

Ranged and thrown weapons each have a listed range increment, and attacks with them grow less accurate against targets farther away. As long as your target is at or within the listed range increment, also called the first range increment, you take no penalty to the attack roll. If you're attacking beyond that range increment, you take a –2 penalty for each additional increment beyond the first. You can attempt to attack with a ranged weapon or thrown weapon up to six range increments away, but the farther away you are, the harder it is to hit your target.

For example, the range increment of a crossbow is 120 feet. If you are shooting at a target no farther away than that distance, you take no penalty due to range. If they're beyond 120 feet but no more than 240 feet away, you take a –2 penalty due to range. If they're beyond 240 feet but no more than 360 feet away, you take a –4 penalty due to range, and so on, until you reach the last range increment: beyond 600 feet but no more than 720 feet away, where you take a –10 penalty due to range.

Armor Class

Attack rolls are compared to a special difficulty class called an Armor Class (AC), which measures how hard it is for your foes to hit you with Strikes and other attack actions. Just like for any other check and DC, the result of an attack roll must meet or exceed your AC to be successful, which allows your foe to deal damage to you.

Armor Class is calculated using the following formula.

Armor Class = 10 + Dexterity modifier (up to your armor's Dex Cap) + proficiency bonus + armor's item bonus to AC + other bonuses + penalties

Use the proficiency bonus for the category (light, medium, or heavy) or the specific type of armor you're wearing. If you're not wearing armor, use your proficiency in unarmored defense.

Armor Class can benefit from bonuses with a variety of sources, much like attack rolls. Armor itself grants an item bonus, so other item bonuses usually won't apply to your AC, but magic armor can increase the item bonus granted by your armor.

Penalties to AC come from situations and effects in much the same way bonuses do. Circumstance penalties come from unfavorable situations, and status penalties come from effects that impede your abilities or from broken armor. You take an item penalty when you wear shoddy armor.

Spell Attack Rolls

If you cast spells, you might be able to make a spell attack roll. These rolls are usually made when a spell makes an attack against a creature's AC. 

The ability modifier for a spell attack roll depends on how you gained access to your spells. If your class grants you spellcasting, use your key ability modifier. Innate spells use your Charisma modifier unless the ability that granted them states otherwise. Focus spells and other sources of spells specify which ability modifier you use for spell attack rolls in the ability that granted them. If you have spells from multiple sources or traditions, you might use different ability modifiers for spell attack rolls for these different sources of spells. For example, a dwarf cleric with the Stonewalker ancestry feat would use her Charisma modifier when casting meld into stone from that feat, since it's a divine innate spell, but she would use her Wisdom modifier when casting heal and other spells using her cleric divine spellcasting.

Determine the spell attack roll with the following formula.

Spell attack roll result = d20 roll + ability modifier used for spellcasting + proficiency bonus + other bonuses + penalties

If you have the ability to cast spells, you'll have a proficiency rank for your spell attack rolls, so you'll always add a proficiency bonus. Like your ability modifier, this proficiency rank may vary from one spell to another if you have spells from multiple sources. Spell attack rolls can benefit from circumstance bonuses and status bonuses, though item bonuses to spell attack rolls are rare. Penalties affect spell attack rolls just like any other attack roll—including your multiple attack penalty. 

Many times, instead of requiring you to make a spell attack roll, the spells you cast will require those within the area or targeted by the spell to attempt a saving throw against your Spell DC to determine how the spell affects them. 

Your spell DC is calculated using the following formula.

Spell DC = 10 + ability modifier used for spellcasting + proficiency bonus + other bonuses + penalties

Perception

Perception measures your ability to be aware of your environment. Every creature has Perception, which works with and is limited by a creature's senses. Whenever you need to attempt a check based on your awareness, you'll attempt a Perception check. Your Perception uses your Wisdom modifier, so you'll use the following formula when attempting a Perception check.

Perception check result = d20 roll + Wisdom modifier + proficiency bonus + other bonuses + penalties

Nearly all creatures are at least trained in Perception, so you will almost always add a proficiency bonus to your Perception modifier. You might add a circumstance bonus for advantageous situations or environments, and typically get status bonuses from spells or other magical effects. Items can also grant you a bonus to Perception, typically in a certain situation. For instance, a fine spyglass grants a +1 item bonus to Perception when attempting to see something a long distance away. Circumstance penalties to Perception occur when an environment or situation (such as fog) hampers your senses, while status penalties typically come from conditions, spells, and magic effects that foil the senses. You'll rarely encounter item penalties or untyped penalties for Perception. 

Many abilities are compared to your Perception DC to determine whether they succeed. Your Perception DC is 10 + your total Perception modifier.

Perception for Initiative

Often, you'll roll a Perception check to determine your order in initiative. When you do this, instead of comparing the result against a DC, everyone in the encounter will compare their results. The creature with the highest result acts first, the creature with the second-highest result goes second, and so on. Sometimes you may be called on to roll a skill check for initiative instead, but you'll compare results just as if you had rolled Perception. 

Saving Throws

There are three types of saving throws: Fortitude saves, Reflex saves, and Will saves. In all cases, saving throws measure your ability to shrug off harmful effects in the form of afflictions, damage, or conditions. You'll always add a proficiency bonus to each save. Your class might give a different proficiency to each save, but you'll be trained at minimum. Some circumstances and spells might give you circumstance or status bonuses to saves, and you might find resilient armor or other magic items that give an item bonus.

Fortitude saving throws allow you to reduce the effects of abilities and afflictions that can debilitate the body. They use your Constitution modifier and are calculated as shown in the formula below.

Fortitude save result = d20 roll + Constitution modifier + proficiency bonus + other bonuses + penalties

Reflex saving throws measure how well you can respond quickly to a situation and how gracefully you can avoid effects that have been thrown at you. They use your Dexterity modifier and are calculated as shown in the formula below.

Reflex save result = d20 roll + Dexterity modifier + proficiency bonus + other bonuses + penalties

Will saving throws measure how well you can resist attacks to your mind and spirit. They use your Wisdom modifier and are calculated as shown in the formula below.

Will save result = d20 roll + Wisdom modifier + proficiency bonus + other bonuses + penalties

Sometimes you'll need to know your DC for a given saving throw. The DC for a saving throw is 10 + the total modifier for that saving throw.

Most of the time, when you attempt a saving throw, you don't have to use your actions or your reaction. You don't even need to be able to act to attempt saving throws. However, in some special cases you might have to take an action to attempt a save. For instance, you can try to recover from the sickened condition by spending an action to attempt a Fortitude save.

Basic Saving Throws

Sometimes you will be called on to attempt a basic saving throw. This type of saving throw works just like any other saving throw—the “basic” part refers to the effects. For a basic save, you'll attempt the check and determine whether you critically succeed, succeed, fail, or critically fail like you would any other saving throw. Then one of the following outcomes applies based on your degree of success—no matter what caused the saving throw.
Critical Success You take no damage from the spell, hazard, or effect that caused you to attempt the save.
Success You take half the listed damage from the effect.
Failure You take the full damage listed from the effect.
Critical Failure You take double the listed damage from the effect.

Fortune and Misfortune Effects

Fortune and misfortune effects can alter how you roll your dice. These abilities might allow you to reroll a failed roll, force you to reroll a successful roll, allow you to roll twice and use the higher result, or force you to roll twice and use the lower result.

You can never have more than one fortune effect or misfortune effect come into play on a single roll. For instance, if an effect lets you roll twice and use the higher roll, you can't then use Halfling Luck (a fortune effect) to reroll if you fail. If multiple fortune effects would apply, you have to pick which to use. If two misfortune effects apply, the GM decides which is worse and applies it.
If both a fortune effect and a misfortune effect would apply to the same roll, the two cancel each other out, and you roll normally.

Skill Checks

Pathfinder has a variety of skills, from Athletics to Medicine to Occultism. Each grants you a set of related actions that rely on you rolling a skill check. Each skill has a key ability score, based on the scope of the skill in question. For instance, Athletics deals with feats of physical prowess, like swimming and jumping, so its key ability score is Strength. Medicine deals with the ability to diagnose and treat wounds and ailments, so its key ability score is Wisdom. The key ability score for each skill is listed in Chapter 4: Skills. No matter which skill you're using, you calculate a check for it using the following formula. 

Skill check result = d20 roll + modifier of the skill's key ability score + proficiency bonus + other bonuses + penalties

You're unlikely to be trained in every skill. When using a skill in which you're untrained, your proficiency bonus is +0; otherwise, it equals your level plus 2 for trained, or higher once you become expert or better. The proficiency rank is specific to the skill you're using. Aid from another character or some other beneficial situation may grant you a circumstance bonus. A status bonus might come from a helpful spell or magical effect. Sometimes tools related to the skill grant you an item bonus to your skill checks. Conversely, unfavorable situations might give you a circumstance penalty to your skill check, while harmful spells, magic, or conditions might also impose a status penalty. Using shoddy or makeshift tools might cause you to take an item penalty. Sometimes a skill action can be an attack, and in these cases, the skill check might take a multiple attack penalty. 

When an ability calls for you to use the DC for a specific skill, you can calculate it by adding 10 + your total modifier for that skill.

Notating Total Modifiers

When creating your character and adventuring you'll record the total modifier for various important checks on your character sheet. Since many bonuses and penalties are due to the immediate circumstances, spells, and other temporary magical effects, you typically won't apply them to your notations. 

Item bonuses and penalties are often more persistent, so you will often want to record them ahead of time. For instance, if you are using a weapon with a +1 weapon potency rune, you'll want to add the +1 item bonus to your notation for your attack rolls with that weapon, since you will include that bonus every time you attack with that weapon. But if you have a fine spyglass, you wouldn't add its item bonus to your Perception check notation, since you gain that bonus only if you are using sight—and the spyglass!—to see long distances.

Special Checks

Some categories of checks follow special rules. The most notable are flat checks and secret checks. 

Flat Checks

When the chance something will happen or fail to happen is based purely on chance, you'll attempt a flat check. A flat check never includes any modifiers, bonuses, or penalties—you just roll a d20 and compare the result on the die to the DC. Only abilities that specifically apply to flat checks can change the checks' DCs; most such effects affect only certain types of flat checks.

If more than one flat check would ever cause or prevent the same thing, just roll once and use the highest DC. In the rare circumstance that a flat check has a DC of 1 or lower, skip rolling; you automatically succeed. Conversely, if one ever has a DC of 21 or higher, you automatically fail.

Secret Checks

Sometimes you as the player shouldn't know the exact result and effect of a check. In these situations, the rules (or the GM) will call for a secret check. The secret trait appears on anything that uses secret checks. This type of check uses the same formulas you normally would use for that check, but is rolled by the GM, who doesn't reveal the result. Instead, the GM simply describes the information or effects determined by the check's result. If you don't know a secret check is happening (for instance, if the GM rolls a secret Fortitude save against a poison that you failed to notice), you can't use any fortune or misfortune abilities on that check, but if a fortune or misfortune effect would apply automatically, the GM applies it to the secret check. If you know that the GM is attempting a secret check—as often happens with Recall Knowledge or Seek—you can usually activate fortune or misfortune abilities for that check. Just tell the GM, and they'll apply the ability to the check.

The GM can choose to make any check secret, even if it's not usually rolled secretly. Conversely, the GM can let you roll any check yourself, even if that check would usually be secret. Some groups find it simpler to have players roll all secret checks and just try to avoid acting on any out-of-character knowledge, while others enjoy the mystery.