Less Dice, More Decisions: House rules for OSR and D&D (Part 3)

Today I am sharing my house rules for action tests in OSR games. These rules were originally written to replace the percentile Thief skills found in Basic Fantasy RPG and B/X D&D. They grew out of the Ability Test table in the appendix of Basic Fantasy 3rd.


Part 3: Thief Skills and Action Tests

Action Tests

The Problem

In many OSR games Thieves get skills and no one else does. For me this doesn’t work because if my players want to try something I want to give them a chance whichever class they are playing but at low levels if I give them anything more than a 10% chance of success they will be almost as good a Thief as the actual Thief. A common suggestion is to ask players to roll under the appropriate stat on a d20 but that won’t improve as the characters gain experience and it doesn’t integrate well with most Thief skill systems, where the Thief’s player would probably rather roll against his Dex of 13 than his Pickpocket skill of 20%.

My Fix:

When a PC attempts a challenging task, the player must roll an Action Test. Roll a d20, the task succeeds on a 17 or higher. The player must apply the most appropriate Ability Modifier to the roll, and Thieves (or experts or similar) get a bonus equal to an equivalent level Fighter’s attack bonus, other classes gain +1 every two levels. Finally, if the activity is related to your class (e.g. tactics for a Fighter, climbing for a Thief) roll twice and use the higher roll.

So this is a d20 roll for pretty much anything not already covered by combat, spell casting, turning undead and similar. It does replace Thief skills. So use this for climbing, navigation, negotiation, perception, building stuff, breaking stuff, sailing, etc.

This rule isn’t as simple as my others but it does do a lot of work, providing a system of ability tests for all classes and balancing and simplifying the Thief’s skills.


Party Action Tests

The Problem

Those times when you need to check if anyone in the party notices the strange blue slime on the ceiling so everyone rolls a Perception test and it’s pretty much given that there will always be at least one pass, so nothing can ever surprise them. Or the party are sneaking into the Lord’s manor so you need stealth checks and, thanks to the law of averages someone will always fail, which gets annoying when your players want to have a chance of occasionally getting past the guards without a fight.

My Fix:

Have one player roll a single Action Test for the whole party. If it is a situation where you only need to know if one character has succeeded (a Perception test or a Lore check maybe), roll 1d20 with a bonus equal to the highest experience level in the group and also the single highest relevant Ability Modifier. On the other hand, if it is a situation where you need to know if all of the PCs succeed (a Stealth test or a check to sail a large boat through a storm), roll 1d20 with a bonus equal to half the lowest experience level in the group and again the single highest relevant Ability Modifier in the party. On a roll of at least 17 the group succeeds.

Optionally, you can allow each group to have a speciality where they get to roll twice and take the highest if the Party Action Test is related to the group’s raison d’etre. So a group of mercenaries might get to roll with advantage when they are testing to spot an ambush or train a militia while a group of criminals might get advantage when rolling stealth or deception checks.
This rule can be a little complicated to explain, but it is simple enough in play and often better represents what is actually going on in the fiction. I like to rotate which player rolls group tests to keep everyone involved.


5 thoughts on “Less Dice, More Decisions: House rules for OSR and D&D (Part 3)

  1. Action Tests: I think this is a good system. It immediately puts the Thief ahead of the other classes, and keeps them there, while letting everyone get better at things. That said, I can’t help but feel that needing a 17+ is a bit harsh.

    A 1st level character with a +1 in the relevant stat, has only a 25% chance of success at that difficulty. Given that people already underestimate their probability of success, that’s going to leave people feeling unlucky most of the time. Rolling under stat will on average give you a 50% chance of success (assuming 3d6 down the line), or 60% if you use some other more generous stat generating system — and that’s where I’d pitch my baseline.

    So, a 50-60% chance of success at a standard task, that’s a 10+ on the d20 (plus bonus). Gaining 1/2 your level, that means success only becomes assured around level 16-20. Meanwhile the Thief, gaining their full level bonus, is better than the other classes from the start, and has assured success around level 8. That seems much more reasonable, and there’s still plenty of room for failure at the early levels.

    Also, you can easily say a difficulty of 15 or even 20 for harder tasks (since one size difficulty does not fit all). I’d refrain from making difficulties scale with level, that just means you’re on a treadmill. Instead, keep things typically at 10, but let players try to do things in a more flashy way (e.g. knocking down the door with their pinky), and only add in the higher difficulties when it makes sense. Finally, you could chuck in 5e’s Advantage / Disadvantage mechanic in place of situational bonuses, because it’s a good mechanic and deserves to see more action.

    1. Addition: Thief’s skills are considered supernatural (e.g. hide in shadows, move silently, climb sheer walls), but anyone can try the mundane version (e.g. hide behind objects, move quietly, climb a rough wall).

      There are two ways I can see of handling this:
      1) The Thief rolls (with their full level bonus) and succeeds on 10+, but the supernatural version triggers if they get 15+.
      2) The Thief gets to roll against 15 for the supernatural version; if they fail they get to roll again against 10 for the mundane version.

      The 2nd way mathematically benefits the Thief, and feels different (no one else gets a reroll), but is more rolling, especially with Ad/Disad, so I would favour the 1st way in game.

      1. And as for supernatural Thieves, I never liked that idea. It’s a bit too fiddly to implement and sometimes hard to justify in the fiction.

    2. I went with a base difficulty of 17+ for a number of reasons. Firstly I only wanted players to be rolling if the task is difficult; if the task can be completed without risk given enough time then I’d just let the players achieve whatever it is and mark the time as passed.

      Secondly, first level characters usually aren’t very capable. Even at 20% this system is in the region of 1st level B/X Thieves or of 1/6 skill checks in Lamentations of the Flame Princess.

      Also, these low chances of success are for characters who are trying to perform an action outwith their own class. If they are trying to do something which is covered by their class then a 17+ test will pass 36% of the time and with just a single +1 for a Ability Modifier the chance of success increases to 44%.

      So using the above system, any task is at least possible. Levelling up and high stats help but not as much as having the right class. Also, no PC ever has a 100% chance of passing, which I like.

      1. I’m not sure how, but I totally missed that you’d included the Advantage in there already. Yes, that makes a huge difference. I think it’s just that I like to see more rolls, so err towards easier ones.

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