CD10 Core

This article assumes that you are familiar with tabletop roleplaying games (TTRPGs) and that you understand the basic concepts of what a TTRPG is. If you have not, you should start here: What is a TTRPG?

The CD10 system uses the d10 and it should be the only die you need to play a game with CD10. Other types of dice can be used to faciliate randomness but you are not required to have any more than a single d10 to play. In difference from most games the 0 on a d10 is considered an actual 0, not a 10.

Special Case [d100]

In some cases the game calls for a d100. To roll a d100, simply roll the d10 twice, counting the first as ten's unit and the second as single's unit. So if you roll a 6 and an 8, the result is 68. Even with a d100, 0 on the die is a 0. So rolling a 0 and then a 0 is a result of 00.

Character stats

In roleplaying games, characters generally have a number of numerical statistics that determine how they are. While most RPG systems have a set of basic attributes that determine things like strength, intelligence and other physical and mental statistics, CD10 uses a system of fluid traits instead. No two characters are the same, as traits are up to the player to pick and choose from. Not having a trait means that a character is average in regards to the trait, and it is not noted on the character sheet. Traits are more flexible than base attributes and can represent a wide variety of personality traits, physical characteristics and even more vague concepts such as Love and Status. Traits are explained in more detail in CD10 Core: Traits.

A character in CD10 is built up of a backstory, species, a set of traits, a set of skills and optionally a set of abilities taken from a module. Abilities depends on the setting. A magical setting would see the character have magical abilities, while a modern or futuristic setting could see characters have mutations, cybernetics or psionic abilities. Each of these stats tell you something about how the character will perform in the game.


The character's background is among the most important parts of a character and even though it isn't displayed on the character sheet or provide any numbers for gameplay, the backstory is what helps the player guide which traits, skills and abilities to choose for the character. In addition, the background sets up a couple of important events and people for the GM to use in future stories.


Depending on the setting, the species of the character affects a few things including a set of starting traits and possibly abilities in addition to providing a social context for the story.


The skills of a character define what they have learned in life and how good they are at performing them. Most anyone who has played roleplaying games are familiar with skills and how you perform "skill checks" to overcome challenges in the game.


Traits are descriptors of the character and can describe things like physical prowess, mental faculties, quirks, personality and even things like fate. Traits help define a character and thanks to their integration into the core of CD10, traits can play a large part mechanically, giving your choices real gameplay impact.

Traits can also be things that a character can do or things they possess that aren't either skills or equipment. Mutations, psionics and cybernetic equipment and certain physical attributes like having a tail or wings can also be traits.


Base Die
Keeper of the Tales, the one who runs the narrative and abjudicates rules.
Set by the Keeper, a number which the player must overcome with their skills. Shortened to DC.
The combined value of a d10, a skill and optionally a trait.
The outcome of a skill check. Can be fumble, fail, status quo, success or perfection.
The remaining points when Difficulty has been subtracted from the Result.
Skill Checks
D10 + Skill + Trait vs Difficulty


Roll a 0, and also fail the re-roll, or roll -10 below difficulty.
Result is below difficulty, or roll a 0 then beat the difficulty on the re-roll.
Status Quo
Result is equal to difficulty.
Result is above difficulty.
Result is +10 above difficulty.
Alternate fumble
Roll a 0, then another 0.

Common difficulties

3: Easy
6: Normal
9: Challenge
12: Hard
15: Very Hard
18: Send help
21+: You want to do what now?
Rule of 9
On landing a 9 on the die, add 9 to your result and roll again.
Rule of 0
On landing on 0 on the die, the outcome is an automatic fail, and you roll again. If you do not manage to beat the difficulty on the re-roll, you have fumbled the roll.
Internal modifier
Always calculated by the person rolling the die. Usually the player. A modifier that affects your character. Usually injury, debilitation, stimulants or traits. These modify the roll of the die by increasing it (d10+modifier) or reducing it (d10-modifier)
External modifier
Always calculated by the Keeper. A modifier that makes a certain task harder to perform. The Keeper applies this to the Difficulty value. Usually something like weather, temperature, circumstances etc.

Basic checks

Whenever a character tries to do something where the outcome is uncertain, a Check is called for by the Keeper. In order to make a check you roll your d10, optionally add your relevant skill number and optionally a trait that fits the situation and add them all together. The sum of these three things are called the Result. The Result needs to be higher than the Difficulty to be a success. We'll cover Difficulty below.

Blank checks

A check that is made without a skill is called a Blank Check. This means that your character has no talent, skill or training for whatever they are trying to do. Traits may still apply to blank checks. Blank checks are unlikely to succeed at standard difficulty (9), but for easy tasks it's about a 50% chance.

Blank checks may only be performed on so called "Core" skills. See CD10 Core: Skills for details on what is defined as a core skill. Professional skills require training and can't be blank-checked.

Skill check summary

Skill (0 to 8) + Trait (-4 to 4) + D10 (0 to 9) vs Difficulty (3 to 18)


The Difficulty is a value set by the Keeper that the character must overcome in order to succeed their check. The Result must be equal to or higher than the Difficulty for the check to have a positive outcome. Failing to beat the Difficulty results in a failed check. There are additional outcomes to a check, commonly known as critical success and critical failure in most RPG systems, and one additional one, but we'll get to those in a minute. For now, all you need to remember is that if you are equal to or above the difficulty, the check is a success and if you are below, it is a failure.

How hard is hard?

Difficulty varies between 1 and 18 but can technically get infinitely high. When the Keeper alters Difficulty, she will generally scale it in steps of three. Making something harder is +3 to Difficulty and vice versa. Unless something else specifies it, the base Difficulty of a check is assumed to be a challenge to the character and has a value of 9. Any deviation is either due to rules or Keeper abjudication. The Keeper can scale difficulty by any number, using +1 or -2 as she pleases, but the steps of three are good "anchor points" for Difficulty.

Value Difficulty
3 Easy
6 Normal
9 Challenge
12 Hard
15 Very Hard
18 Send help
21+ You want to do what now?


A concept that returns often in CD10 is Excess. Excess is the value you get when you subtract the Difficulty from the Result of a check. For instance, if you rolled a 6 on the die and had a skill value of 4, your Result is 10. The Keeper has set the Difficulty to 7 for that particular check. The Excess then is 10-7 = 3. Excess is not always used for checks, but in some cases, Excess can be used to add additional bonuses, such as extra damage on attack rolls or as a guideline for the Keeper to determine finer details of an outcome.

Opposed checks

An opposed skill check is done when you are trying to overcome an opponent in any way. This is usually used when bartering, sneaking, hiding or looking for someone who is hiding. An opposed check is performed by both parties against a set Difficulty. The Difficulty can be different for each individual, given the situation. Once both have performed their check, their Excess is compared and the higher is the winner. A typical case of an opposed check is a combat check.

Drax is hiding from a band of goons who are on the lookout for him. He dives into a nearby alley and hides in a pile of trash. Drax attempts a Stealth check to hide and rolls 5 and adds his Stealth skill, which is 2, for a total of 7. Not a great Result. It's in fact lower than the 9 DC the Keeper decided on.

The goon who is looking for him makes a Perception check with a skill value of 4 and the die lands on 6 for a total of 10. Given that the goon is actively searching for Drax and knows he's somewhere around, the Keeper decides that in spite of everything, the goon is under a DC 9 to find Drax. With his Result of 10, his Excess is 1, which is higher than Drax' -2, and spots him hulking among some rubble.


Crap D10 by Tobias Linder

There are five Outcomes to a check depending on what the Result is in relation to the Difficulty. The Outcome of a skill check can be a critical failure (called a fumble), a failure, status quo, success or critical success (called perfection). Depending on the situation and judgement call for the Keeper, these mean different things.

The two easiest are success and failure. They're fairly self-explanatory. The character either successfully do what they intended to do, fails to make any progress or completely fails what they intended to do. A check-mark (✔) is noted next to a skill that you fail a check for. More on that later.

Exactly how they succeed or fail is up the Keeper to describe in narrative. The three outcomes beyond simple success and failure, such as the Status Quo, might need some explaining.

Failing forward

A failure should not be a dead end for a character. The options shouldn't be between absolute success or failure. It should determine whether or not the character successfully perform the action as intended or not.

An example is when a character attempts to sneak past a guard. Failing the check does not mean that they are immediately spotted, but the guard heard or saw something and he's now more alert. Or the character attempts to jump from one rooftop to the next. Instead of falling to the ground (and potential death), a failure means that the character slips and just barely misses the jump. Left hanging on the edge they now need rescue or must climb up on their own, costing potentially valuable time.


A fumble is a catastrophic failure. The planets aligned with the stars and decided that today was not your day. A fumble should be a narratively exciting failure without being immediately fatal. It should involve a stronger failure such as instead of simply missing the opponent, the character slips on the ground and falls, their weapon jams or they risk hurting themselves. As the Keeper, take the opportunity to be creative and describe what happens. A fumble should have an additional penalty beyond simple failure, be it economic, social or physical (such as injury or exertion).

The Outcome is a fumble if one of two things happen:

* The result is 10 below the Difficulty of the check (for instance a result of 3 on a DC 15 check).

* The d10 lands on a 0 on any check. This is not a fumble just yet. But in this case you get a second chance to try and beat the check. Should the Result be below the Difficulty on this second chance, the Outcome becomes a fumble. If you succeed the check on the re-roll after the 0, the Outcome is a regular failure.

Alternate fumble rule

If the Keeper feels that fumbles are too common and wants to reduce the frequency she can apply an alternate rule for fumbles where they only occur either if the Result is ten below difficulty or if the player rolls a 0 followed by another 0. This means that the player does not need to beat the Difficulty on the re-roll, only not roll another 0.


A perfection is the opposite of a fumble. It's when the stars aligned and the sun shone upon your day. A perfection is something beyond a simple success. The Keeper can decide on a myriad of things that can be the result of a perfection such as performning the task ridiculously fast, slick, quietly or smoothly. For combat the additional success already provides extra damage so there is no need to enhance it further.

The Outcome of a check is a perfection if:

* The Result is 10 or more above the Difficulty of the check (for instance a result of 23 on a DC 13 check).

Status Quo

The status quo, depending on what action is taken, could be a success or a failure but should in almost every case be a success. The Keeper can use the status quo outcome to build tension, allowing the character to just barely succeed by the skin of their teeth. The Keeper should, in almost every case, add some form of penalty to the success. The character succeeds with what they intended to do but they take a lot of time doing so, only finished just as time is running out, or perhaps they make an awful racket doing what they meant to do. The options are endless for how the Keeper can modify what happens but keep in mind that in almost every case a status quo is a success. A Status Quo can usually be told as "You succeed, but ..."

The Outcome of a check is a Status Quo if:

* The Result is exactly the same as the difficulty (for instance a result of 12 on a difficulty 12 check).

* On an opposed check, both opponents' Results are the same.

If the check is an opposed check, neither side of the involved manage to make any headway.

The Rule of 9 (R9)

When you roll a 9 you add 9 to your Result as usual, but you now get to roll again. You add the re-rolled die to your Result again. You do this until you roll no more 9s. Should the die fall on 0 after you have rolled a 9 the rule of 0 (below) does not apply, the die simply counts as 0 value and you stop rolling.

Drax is attempting to shoot a goon with his submachinegun. He has 6 in the skill and rolls a 9. Drax cheers and adds 9 to his Result and rolls again. The dice gods are with him, as he rolls yet another 9! He adds that to the result and rolls again. The die lands on a 0. Since he didn't roll any more 9's, he adds his result together 6+9+9+0 = 24. That goon is going to have a bad day.

The Rule of 0 (R0)

If the die lands on 0 the check automatically fails. You reroll the check in order to try and avoid disaster. If you beat the Difficulty on the re-roll, the check is just a regular failure. But if you fail the re-roll, the check is considered a fumble. If the check is an opposed check (see below), no re-roll is needed. Instead the check is then a fumble if the Result is lower than the opponents.

In another universe, Drax is attempting to shoot another goon with his submachinegun. He has 6 in the skill and rolls a 0. Consumed by dread, Drax rolls again. The dice gods are with him, as he rolls an 8. His Result therefore is 6+8=14, which is a success. Thanks to his post-0 success, Drax "just" fails and avoids fumbling the check.

Skills and Traits

Commonly in role-playing games a character has a couple of basic ability scores such as strength, intelligence, dexterity, stamina etc. These values may affect things such as skills and basic abilities. CD10 is a traits-based system and doesn't have any basic ability scores like that. CD10 instead relies on a system of skills and traits to describe a character. Skills are what your character has learned and skills they can use in everyday situations. It could be things like communication skills (Etiquette or Persuasion) or it could be combat skills (Brawl or Handguns).

Skill attributes

The things you may look for if you're familiar with RPGs in general are the base attributes like strength and intelligence. These things are skills in CD10 and are trainable just like any other skill. If you don't possess Reasoning (CD10's equivalent of "intelligence" or "smart"), you aren't dumb or have the intelligence of a wet rock, you are simply somewhat below average and haven't trained yourself in reasoning, logic and using your brain for problem solving. Same for the other skills.

Traits can be almost anything, within reason. Traits can describe basic physical abilities but they can also describe more vague things like influence, honesty and love. Traits also have an inherent connotation of being "good" or "bad", expressed as positive and negative traits. This is relative to the character, so it's how this trait affects the character. Loyal would in most people's eyes be a positive thing, so this must be a positive trait? From the character's perspective being loyal is a drawback, as it limits your freedom, so being loyal is a negative trait for the individual. But most people will likely respond positively to it.

Traits are applied to checks just like skills, but like skills they only apply to relevant checks, but what is a relevant check is a bit more fluid than for skills. Whether or not a trait applies to a particular check is always up to the Keeper. If you believe that a particular trait should apply you can ask the Keeper and they may accept or deny the request. The Keeper's decision is final.

The "One Trait Rule"

Only a single trait may apply to a single check. If there are more than one trait that would apply to a check the player (or Keeper) must choose only one of them.

Exception to the "One Trait Rule"

r At the Keeper's discretion if two traits would apply and one is positive and the other negative, the Keeper can rule to use the difference between the two as a modifier for a check.

How good is good?

A character only has two main things that describe their overall ability. The first is the number of skills and their respective values, the second is their traits. Below you can see the skill levels and a table over the probability to succeed on a default Difficulty 9 check.

Skill values

Skills range from 1 to 8 in value normally, but can get as high as 12 if the player spends a significant amount of effort increasing them. The skill value determines how proficient your character is at that particular skill. Higher is better.

A skill of 4 is roughly equivalent to a 1 in 2 chance to succeed at a normal difficulty (DC 9) task assuming no other modifiers. To achieve maximum skill chance on a DC 9 check, you must have a skill value of 8. Because of the Rule of 0, you can never achieve more than roughly 90% chance to succeed any given check, regardless of skill value. However, higher skill values allow you to attempt more difficult tasks and deal with negative modifiers better. Each level of a skill carries with it a +10% chance to succeed on a DC 9 check.

Value Equivalent
0 Nothing
1 Beginner
2 Hobbyist
3 Gifted Amateur
4 Competent Amateur
5 Good Professional
6 Skilled Professional
8 Master
10 Legendary Master
12 Never before surpassed

Needless skill checks

The Keeper is encouraged to not call for checks for mundane things like driving a car, walking down the stairs or performing day to day activities. There is no narrative purpose to those checks and they don't present any tension or affect the story in any significant way. Only call for a check if there is both a chance of failure and there is a narrative purpose to either a success or failure. Otherwise you are just wasting everyone's time with meaningless checks.

Trait values

Traits can vary from -4 to 4 and they are usually neither straight up good nor bad. They are highly dependent on circumstances. In general though, you can consider 1-2 to be within normal variation for a person, 3 being highly unusual and 4 being almost unheard of.

Internal and External modifiers

Skills and Traits are innate to the character and thus affect the dice roll of the character instead of modifying the Difficulty of the check. So when a negative trait is expressed as -2, it means it modifies the check as it is rolled for the character, not the set Difficulty of the check. This is an important distinction to make, both as a player and as a Keeper. Things such as injuries, traits and skills are all innate to the character themselves and affects the character's ability to perform and thus affect the value of the roll through modifiers. Skills are always positive, traits can be both and injuries are always negative.

External circumstances such as range disadvantage or bad weather all affect the difficulty of the check and are applied by the Keeper. The Keeper usually describes this narratively by saying that the bad weather makes this check harder. She doesn't have to state exactly how much harder it is (that is, she doesn't have to divulge the exact difficulty number), but she should always tell the player when she's making things harder or easier for them, so the player is aware of it.

Players are responsible for adding up their personal modifiers when rolling and then telling the Keeper what their Result (or Excess) was. The group has to decide what they prefer to report, either the Result or Excess. Both ways work and put a small calculation task either on the player or on the Keeper. They'll roll the die, add their skill, add the relevant trait (if accepted by the Keeper) and also subtract any negative modifiers (such as from injuries or negative traits) then tell the Keeper the total Result or Excess.

Do not mix the two modifiers up, since an internal modifier is the responsibility of the player and an external modifier is the responsibility of the Keeper, and is also usually not told to the player. A -3 external modifier reduces the Difficulty by -3, making the check easier, while a -3 internal modifier makes things harder by decreasing the value of the roll itself. One is the responsibility of the Keeper, the other the responsibility of the player. Modifiers are commonly clearly marked as internal or external, but if you remember the concept that one is inherent to the character, and another is external, that should make things easier to understand.

An Internal Modifier is the responsibility of the player and is applied to the check the player rolls before reporting the Outcome or Excess to the Keeper.

Internal modifiers are expressed as negative when they are detrimental (by reducing the value of the Result) and positive when supportive (by increasing the value Result).

An External Modifier is the responsibility of the Keeper of Tales and is applied to the Difficulty of the check. The Keeper doesn't necessarily have to divulge what modifiers she applies to Difficulty.

External modifiers are expressed as positive when they are detrimental (by increasing Difficulty) and negative when supportive (by decreasing Difficulty)

Reversing traits

Sometimes traits may be reversed, either by yourself or by the Keeper. For instance, the trait Small is generally considered to be a bad thing, thus a negative trait. If you're small you're not as strong, sturdy and generally looked down upon, can't reach as far etc. But when hiding, being small is definitely an advantage. In that case you add to the value of the roll by the value of the trait, instead of reducing it. Whether a trait is reversed or not it remains an internal modifier.

Saving Throws

Some systems implement some form of "save" or "saving throw" based on a basic attribute (like strength or wisdom) in order to resist some form event.

These do not exist in CD10. Instead, all checks are skill checks, regardless of if the character possesses the skill or not. A skill check to avoid a sprung trap, for instance, may be an Acrobatics check. If the character doesn't posses that skill, they can use a related skill or trait or even make a blank check.

Hero Points

Experience points gathered by the player can be spent as Hero Points. A player can spend up to two hero points per session. They allow increasingly larger changes to fate and both can be spent on one roll or they can be spread out over the entire session.

A hero point spent allows the player to either re-roll a single check, regardless of outcome, or pre-emptively to roll 2D10 for a check. If spent to re-roll the check, the player must accept the re-rolled value and cannot go back to the first result. However if the roll is not to their liking the player may spend a second hero point. In both cases the rule of 0 does not apply to the check.

Hero points are a vital part of the system and players should be acutely aware of their existance. CD10 is a high lethality game where a single slash or bullet can be all that stands between you and death. Hero points help save characters from freak accidents by altering fate, but they will not save a character from repeated bad decisions. Be aware of your hero points, but do not spend them willy nilly!

The second hero point spent allows for shifting the Outcome of a check one step in either direction. For instance, if a check came out as a Failure even after a re-roll, the player can spend their second Hero Point to shift the Outcome to a Success (Status Quo is ignored here unless the player specifically wants to shift to a Status Quo). You can only use the second point to shift the Outcome if you spend it immediately after the first, after your reroll.

In essence, Hero Points are meant to be used something like this:   You really, really need to hit a high Result for this check -> Spend a Hero Point to roll 2D10.

You get a bad Outcome on a check and your character risks serious harm or even death -> Spend a Hero Point to re-roll the check.

Articles under CD10 Core

Cover image: CD10 Banner by Mizomei


Please Login in order to comment!
20 Feb, 2020 15:33

[I]Trashes the entirety of his B.I.O.S. rule set   This is a hundred times better and more developed tham wjat I was building, and works almost the same. Cant5 wait to try this system out soon.

Now working on
The Hylian Fantasy
20 Feb, 2020 22:55

Thank you for the kind words! I hope you enjoy, and if you have any questions, feel free to contact me on the Discord server.

Author of prize-winning RPG settings Dark Shadows and Cinders of the Cataclysm. Designer of the narratively focused Celenia D10 RPG System.
22 Feb, 2020 03:11

Your system is coming along nicely! I am loving the theme in your new world, too.

Author of Fillimet, bright fantasy land of possibilities, and Vazdimet, its darker spacefaring future.
22 Feb, 2020 12:12

Thank you! ^_^

Author of prize-winning RPG settings Dark Shadows and Cinders of the Cataclysm. Designer of the narratively focused Celenia D10 RPG System.
18 Jun, 2020 20:55

I mentioned it in discussion before. You have taken some very recognizable rpg elements and not only made them your own, but made with narrative in mind and ease of use. This provides flexibility to keep it simple or get more complicated. A major boon in an industry mired with confusion, errata and complex charts. Game on!

Featured Articles in the Shadow War across Creation by Graylion

18 Oct, 2020 20:55

Thanks, Graylion! That is indeed my goal :)

Author of prize-winning RPG settings Dark Shadows and Cinders of the Cataclysm. Designer of the narratively focused Celenia D10 RPG System.
Fabled Legend Davina
Susanne Lamprecht
25 Mar, 2021 18:50

Celenia is definitely a system which is absolutely inspiring! I am happy to read around here! You did a very great job, as usual!

Check out WIRE, my class- and level-less d20 system here
25 Mar, 2021 19:09

Thank you, Davina <3 Means a lot coming from you ^^

Author of prize-winning RPG settings Dark Shadows and Cinders of the Cataclysm. Designer of the narratively focused Celenia D10 RPG System.
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