# An ability test and Thief skill system for B/X

I’m actually doing it. I’m making my own version of what I think the Basic/Expert rules should have looked like, with dice rolls that are intuitive and level progressions that are consistent, based on my first experiences with the d20 system. I’m probably not gonna use it, and it’s really just an exercise in tinkering around. I don’t think you would get a lot of interested player for a campaign by a new GM with his personal fantasy heartbreaker, but maybe when I have an established OSE campaign running the players might be interested in a less messy version of the rules which still really do the same thing.

It’s really just all the Yora rules put together. Mostly ideas that come from Stars Without Number, Lamentations of the Flame Princess, and Deep Carbon Observatory. But I also got some original ideas of my own. (Which I’m probably not the first person to come up with.)

Where I think B/X really can be improved is some kind of consistent system for ability checks. Hear noise and detect secret doors are a 1 in 6 roll. Thief skills are a percentage roll. Other actions are suggested to be handled by rolling a d20 under the characters most relevant ability score. It’s all over the place. The solution that I’ve come up with is none of the above.

To make a roll to see if a character succeeds on an action that seems plausible to work but success is not certain and there are meaningful consequences for failure, roll 2d6 against a target number based on the character’s most relevant ability score.

For characters with no modifier for the relevant ability, the target number is 7. (Right in the middle for a 2d6 roll, the most common result, and a chance to succeed of 58%, slightly above half.) This number is modified by the ability modifier.

Score Modifier TN Chance
3 -3 10 17%
4-5 -2 9 28%
6-8 -1 8 42%
9-12 +0 7 58%
13-15 +1 6 72%
16-17 +2 5 83%
18 +3 4 92%

This system replaces the Strength modifier for opening doors. (2d6 against TN 5 is about the probability of 1-5 on a d6.) If a task seems particularly difficult, you can tell the player  to roll with -1 or -2, and the majority will intuitively understand that this means 2d6-1 against the same target number as always. (The target numbers should be on the character sheet, like saving throws.)

The very same system to make rolls can also be used to roll for Thief skills instead of 1d100 roll under. This assumes that Thief skills are things that are simply impossible for anyone who isn’t a thief. Climbing walls too smooth to climb on, moving without making any noise, hiding with nothing to hide behind. These are things you can’t take a shot at and hope to get lucky without the special training of the thief class. (For hearing noises, I would go with letting a thief roll against the target number of either his Wisdom or Thief skill, whichever is lower.

## 2 thoughts on “An ability test and Thief skill system for B/X”

1. I do love me some 2d6 action. I haven’t implemented a general skill system or attribute checks in my home game, but if I did it’d almost certainly look a lot like this. Most of my ad hoc systems end up using 2d6 as well.

1. There’s already a couple of 2d6 in B/X, and of course 3d6 for stats, and I always find it elegant.

Barbarians of Lemuria used 2d6 as the standard dice roll.