The Old-School d6 Skill System

My chief design philosophy, and the way I play at the table can be summed up as "Memorable, Minimal, Metal." I don't like to juggle a lot of rules. The main elements of OSR games are combat and skill rolls. Combat rolls are pretty straightforward, so we're going to take a look the d6 skill system works, problems that may arise from it and how to solve those problems.

As someone who grew up with 2nd edition AD&D I was used to skills being incredibly granular and using a lot of different methods of resolution. It seemed natural to me, having first encountered that approach, that complexity and verisimilitude were the best rules philosophy. Moving on to 3e, it was better (blasphemy!), but there was still a skill for everything and they tended to discourage creativity through their strict codification of what was possible with or without a given skill.

By comparison, the d6 skill system is much more general, open-ended and quick at the table. Description and gameplay help to determine success, and then make a die roll if it's important, failure would be interesting, or it's something esoteric or beyond normal human ability. Compare to carefully calculating modifiers and referencing one or two different manuals to find out how many +1's you have- then comes the rules-lawyer v. DM phase, when rules are interpreted by both sides and reconciled before the most equitable DC can be determined, and finally the die roll occurs to resolve the whole sordid affair, and then description and roleplaying ensue, after four phases of bullshit.

The d6 skill system is beautiful.

It flows well. It uses an easily calculable die. Character's skill levels are visible at a glance and require no calculation whatsoever. 3 in 6? Just fucking roll it, don't even need to add. If you use the philosophy of "don't roll unless failure is interesting, don't roll unless there's not another method of resolution, don't roll if you can describe a logical solution", its chunks of 16.5% probability likely don't even pose a problem.

So how do we solve other problems with this elegant system? As I see it, here are the questions that arise:
  1. When do I even call for a roll?
  2. "Oh, she didn't succeed? I try too." (X times where X is number of players)
  3. When should individual rolls be allowed?
  4. Are all difficulties measured by factors of 16.5%?
  5. Do all non-Specialist characters have a uniform 16.5% chance of success in all situations?
  6. How do I modify the chance of success with a degree of consistency?
  7. How do I determine different degrees of success or failure?
1. When do I even call for a roll?
         The classic answers: 
  • When the difference between success and failure would be interesting. 
  • When it's a skill that's not interesting enough to describe but still shouldn't be an automatic success. 
This philosophy kind of assumes player skill. If players don't know they can reason and describe their way out of most basic problems, they'll probably make skill rolls instead- and thus have a lot more failures. The Ref shouldn't hold their hand through this and say "perhaps you should look under the pile of rags", but they should probably give reminders that skill rolls aren't necessary and that players should make a narrative attempt at solving the problem. If they do a good job, circumvent the roll or at least give some kind of bonus.

2. "Oh, she didn't succeed? I try too." (X times where X is number of players)
When a character makes a roll- the first roll- it doesn't just determine success. It determines if it's possible. If you fuck up picking that lock, well, it's simply not possible in these conditions. Might have to do with your actions, might not. It was too damp in the dungeon. You broke the tumbler. It's rusted in place. Who knows, but it's just not possible, you tried, failed, and now you know. 

If a Specialist is going at it, well, of course there's a better chance of success. Why wouldn't they be able to attempt something a less skilled character tried and failed at? Well, I guess that player fucked it up and should have waited for the professional to give it a shot, but they didn't and they broke the lock, crumbled the crevasse they were trying to jump over, scared away the deer, etc. This may be permanent, or for a set amount of time, common sense should prevail.

3. When should individual rolls be allowed?
When should multiple/all players be allowed or required to make a roll? Perhaps every member of the party needs to jump, or swim, or sneak. 
  • Make a single roll for the party. Works fine for initiative, why not group skill rolls? They all jump, swim, sneak or they don't. If it's a 3, well, the Specialist with a 3 in 6 succeeds, the other guys fail. 
  • The first roll still determines if it's possible. If the Specialist succeeds, the others follow her lead, although with less expertise. A bonus may apply. Rolls beyond the first don't cause it to become impossible unless it really makes sense (if player 1 succeeds, it's possible, and player 2 failing doesn't make it impossible thereafter, like players 3 and 4 can't swim anymore)
  • Players with a higher skill level than the guy who made a failed roll can still attempt it. You failed? Well, I guess a 1 in 6 Tinkering skill doesn't cut it, but a 2 in 6 might still have a chance. This does allow a party to sort of game a system by having the unskilled schmoe try it before turning it over to the Specialist. Maybe you want to allow a party to do this because you respect this cleverness, maybe you're sick of their powergaming shit and you say no. Up to you.
  • They can't attempt it again until a year passes and they gain a level. Just kidding, this is a fucking stupid rule.
4. Are all difficulties measured by factors of 16.5%?
They kind of have to be. That's the die type we're using. At least it's calculable because 2 and 3 are factors of 6, and 6 is close to 1/3 of 20- so you know "Oh I have about a 1/3 chance of success" or "Each skill level is about a 3 in 20 chance." Advantage/Disadvantage is a way to make it a bit more granular, because it'll either double chances of success (increments of 33%) or halve them (8.25%), which are still fairly calculable probability-wise.

  • If you really don't like these increments, it's not very hard to swap the skill system out for Call of Cthulhu's percentile roll-under system. At first you'd probably still have 17% chances of success, but players could improve at different rates and give varied skill levels.
  • Using d20 skills is possible but a little harder to do OSR conversions for because it's an ascending system, it's not a whole lot more granular and is kind of hard to substitute "3 in 20" for "1 in 6" in every rulebook and module you read.

5. Do all non-Specialist characters have a uniform 16.5% chance of success in all situations?
          Here's what happens in that situation:
  • If you have a lot of skill rolls it will fuck the players a lot. At low levels, even Specialists suck at a lot of stuff. Maybe this makes players develop creative ways of doing stuff by avoiding rolls, maybe it makes them throw their hands up, who knows. 
  • It kind of has the Cleric problem of "every party needs one of these in order to be viable, so I guess Jeff has to be a Specialist because we already all chose other classes. Sorry, bud." 
  • Choke points like "Will the party be able to find the secret door?" can really grind the game to a halt. Well, you probably should take those out, or at least throw in a redundancy or two to give players a shot at it even if they forget to take a full 10-minute search action in the goblin toilet chamber. They might deserve some bonus XP if they roleplay that they're taking a 10 minute Shit action in the goblin toilet chamber, though. Personally, I would say so.

6. How do I modify the chance of success with a degree of consistency?
Whenever possible I like to use the same die type for things because it's quicker at the table. Keeping a d6 skill system viable while being able to tweak the difficulty is a top priority. I mostly give bonuses rather than penalties, because characters shouldn't fail all the time, and Specialists who've invested a lot of points deserve to have some certainty.
  • Use stat modifiers (mostly bonuses) to alter the roll in PCs favor. Often this only applies to "basic" applications of the skill because if it applies to all instances somebody with a few skill points might always have a 5 in 6, which makes keeping it challenging tough and undermines Specialists. For instance, you can add your Int bonus to repairing your armor, but not to crafting a masterwork suit of plate because there's a big difference in complexity there and it becomes more dependent on expertise than natural talent. It also gives people something else to use their stat modifiers for, because OSR games don't use those a lot.
  • Give Advantage (roll twice, take the better roll). Disadvantage is most likely unnecessary since chances of success are often low anyway. 
  • Modify the skill roll based on circumstances. Their skill level remains the same, but they go from 3 in 6 to 4 in 6 if there's a bunch of drums making it easier to move silently. Likewise, it might go down to 2 in 6 if they're going right by a guard. 
7. How do I determine different degrees of success or failure?
Rolling high is good. If you have a skill above 1 in 6, you want to roll as close to your skill level as possible. A success of 2 is better than 1. A success of 3 is better than 2. And so on.
  • The higher your skill/chance of success, the better you can do when you do succeed. This can be remembered as "roll high under".
  • Roll a d10  if a skill fails to determine relatively what percentage is complete, if necessary. You bashed that door about 10% open before it got lodged. You climbed 40% of the building before you fell. You scared away 70% of the wildlife when you failed to hunt. 
  • Roll a d10 for time spent. I let my players roll Search even when a 10-minute full search would definitely uncover stuff, if they want. If they succeed, it only takes d10 minutes, and they might have a few more minutes before their torch burns out or I make a wandering monster roll. If they fail, it takes d10 extra minutes. They get to choose whether to push their luck or not.
So, now that you've borne with me, here's what can keep the d6 system viable and give it interesting, varied results.
You should not need to roll more than 2 dice to figure something out, and usually you'll keep it to that 1 sweet, sweet die we all love. My main house rules are:
  • Call for rolls only when necessary and interesting. Allow players narrative "outs" when they're clever. Help new players to learn how to be descriptive and clever. Remove choke points.
  • The first roll determines whether an action is possible. In group situations rolling once for the entire party can speed things along. 
  • Multiple rolls for the same action should only be made when something changes- a character with a higher skill level makes an attempt after a failure, the players narrate a different approach, etc.
  • Give stat bonuses and situational modifiers. This should directly modify the chance of success, not be added to the die roll (+1 added to a chance of success is a bonus, +1 added to a roll is a penalty)
  • "Roll high under". The higher the roll, the better, as long as it succeeds. 

The other methods mentioned above might work better for your game, or in certain situations but not in others. Overall, it should always be quick and easy to make a skill roll. Never make two rolls when you can make one. Never make one roll when you can make none.


  1. This is a fantastic post and I think it really gets at the underlying principles of OSR.

    1. Thanks!
      I've been looking at how to remove more skill rolls from games, particularly in a way that doesn't require the Ref to say "you can't do that" for everything or the opposite, reducing the importance of rolls and skill to the point that roleplaying is more a negotiation than a game.
      To me, the biggest problem is #2, every player trying to use the law of averages to succeed at things by trying over and over, grinding things to a halt. I'm particularly proud of the "first roll determines if it's possible" rule, because I think it not only fixes that problem (for me at least) but also contributes to the air of mystery and tension that my game and a lot of gritty OSR games go for.

  2. Great post! The skill system is (in my experience) the hardest thing to sell to new LotFP players. They see that the base chance of success is super low, and hate it... But if you explain, that with a good description they can replace the roll (at least in some cases) they actively start working on their player skills.


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