Game Basics, Part 2

Posted on July 08, 2017

Ability and Skill Checks

Ability Score Checks test a character’s or monster’s talent and training in an effort to overcome a challenge. The GM calls for a check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results.

An ability check is performed by rolling a d20 and adding the modifiers of the two ability scores that most apply to the task at hand, with the goal to meet a difficulty class, or DC, determined by the GM, based on how difficult the GM determines the proposed action to be. Many actions will fall under the umbrella of a primary or secondary skill, as well, in which case the character or monster’s skill proficiency die will be rolled and added to the total as well.

While any two ability scores’ modifiers might apply based on the particular situation, there are a number of common ability checks that come up frequently. These common checks use what are referred to as derived modifiers, which have specific names. They are listed below. Note that some common checks may be approached in more than one manner or influenced by the greater of a selection of ability score modifiers, as indicated. Different combinations of ability score modifiers indicate different approaches to the task at hand, and its assumed that most of the time a character will approach the task in a way which they are strongest suited to succeed.

To resolve an ability check, GM first decides which abilities are relevant to the task at hand. If a particular skill seems to apply as well, that skill’s proficiency die may apply. A player may attempt to convince the GM that two particularly ability scores might be appropriate based on the way the PC is approaching the situation, but the GM’s decision is final and should not be quibbled with once made. Second, the GM decides on the difficulty of the task, represented by a Difficulty Class. The more difficult a task, the higher its DC. The Typical Difficulty Classes table provides guidance about how to set DCs. Finally, the dice are rolled.

Table: Typical Difficulty Classes

Task Difficulty


Very easy




Moderately Easy




Moderately Hard




Nearly impossible

30 +

Determine the total, and apply any additional applicable bonuses and penalties, and compare the total to the DC. If the total equals or exceeds the DC, the check is a success—the creature overcomes the challenge at hand. Otherwise, it’s a failure, which means the character or monster makes no progress toward the objective or makes progress combined with a setback determined by the GM, depending on the nature of the situation calling for the check. The results of passed or failed tests will often be determined by the rules.

Intermediate Rule: For some checks, the margin of success or failure may impact the overall result. Some checks, particularly crafting, determine their results based on a table. Others have margins of success or failure based on the DC, with every five above or below the DC denoting a greater magnitude of success or failure. See the Margin of Success and Failure Table for a general guide, though many effects have their own rules for how Margin of Success impacts them.

Table: Margin of Failure or Success


Success Level

-15 or lower / natural 1

Critical Failure

-14 to -10

Terrible Failure

-9 to -5

Moderate Failure

-4 to -1

Minor Failure

0 to 5

Minor Success

6 to 10

Good Success


Great Success


Fantastic Success


Epic Success

25 and higher

Legendary Success

A number of alternate checks, most of which have to do with the social rules systems, are instead rolled with 2d10 plus the relevant two ability modifiers plus an applicable proficiency die. This creates a bell curves, as most social actions and interactions, barring extraordinary circumstances, are probably going to go fine. Not amazing and not terribly, just fine. A person’s skill and nature has a correspondingly greater impact. The rules will specify when this happens.


-An ability check is:

d20 + 1st ability score modifier + 2nd modifier [+ proficiency die] vs appropriate DC


2d10 + 1st ability score modifier + 2nd modifier [+ proficiency die] vs appropriate DC

For example: d20 + Dex mod + Int mod + d4

-1st mod + 2nd mod is often replaced by a predetermined derived modifier

For example: the above could also be described as d20 + Reflex mod + d4

-Depending on Check: every 5 above or below is another margin of success or failure.

Common Checks and Derived Modifier Names:

Fortitude: Strength plus Constitution

Reflexes: Dexterity plus Intelligence

Willpower: Wisdom plus Charisma

Swiftness: Strength plus Dexterity

Observation: Intelligence plus Wisdom

Concentration: Constitution plus the higher of Intelligence or Wisdom

Presence: The sum of the greatest two modifiers among Strength, Constitution, and Charisma

Charm: Charisma plus the higher of Intelligence or Wisdom

Menace: The sum of the greatest two modifiers among Strength, Intelligence, and Charisma

Design Comments

The intention of this sort of modification to the basic d20 system is to diminish the role of the accuracy metagame in the overall system by applying an averaging effect. While min-maxed characters will hopefully be both less common and mitigated by this system, it also expands the scale of the overall possible results by quite a bit, especially when combined with proficiency dice, which with magical enhancement or in powerful creatures might get as high as +d30.

While a degree of the bounded accuracy environment of 5E is retained, the scale is obviously expanded to some extent, with creatures and characters with multiple high ability scores far more capable of high results than creatures with low or average ability scores. This, with any luck, will lend higher power characters and creatures the appropriate level of shock and awe, so to speak. The sense of great powers clashing.

The DC table is similar to the SRD, but with a few more gradations. I don’t have a good sense for numbers yet, as I’m SUPER early in the design process.

I’ve waffled quite a bit on derived modifiers, particularly in regard to what to call them and whether to have them. They may end up getting cut, but I’ve come back around to keeping them for now. Give them a place on the character sheet and hopefully they won’t be that confusing or overwhelming.

I originally had skills along with the modifiers they are most often paired with, but I'm waffling on the final list of primary skills still. Expect skills in a future update.