The concept of ability checks in BX is simple: When a character tries to do something for which there’s no defined mechanic (like hurling a Volkswagen Beetle), the player can roll against an ability appropriate to what they’re trying to do. The higher their score in that ability, the greater their chance of success.
From a role-playing perspective, ability checks allow characters to get value from all their attribute scores, especially outside their prime requisite. From a mechanical perspective, ability checks provide a fast-yet-logical way to arbitrate unforeseen situations without bogging down play.
While the implementation in BX is dead simple and does the job, I’d like to suggest an improvement that adds nuance to roll results, expands the scope intuitively, and uses a convention already familiar to BX players.
Old School Ability Checks
The D&D Basic Rules introduces us to ability checks:
“There’s always a chance.” The DM may want to base a character’s chance of doing something on his or her ability scores (Strength, Dexterity, and so forth). To perform a difficult task (such as climbing up a rope or thinking of a forgotten clue), the player should roll the ability score or less on 1d20. The DM may give a bonus or penalty to the roll, depending on the difficulty of the action (-4 for a simple task to +4 for a difficult one). A roll of 1 should always succeed, and a roll of 20 should always fail.
Moldvay, D&D Basic Rules, B60. (1981)
Simple enough, though I have a couple of nits to pick:
- There’s a disconnect between mapping the 3-18 ability score range to the 1-20 roll results that allows an automatic 15% chance of success (d20 result of 1-3) or 10% chance of failure (d20 19-20), regardless of the actual ability score. It’s not a huge gap, but it’s uneven and bigger than I like.
- The -4 to +4 modifier scale (including zero) represents a 45% range of adjustment, which is pretty broad without some guidance. My instinct is to confine the modifiers three options (e.g., ±1, ±2, and ±4, for minor, moderate, and major factors, respectively), but even that seems overwrought for what’s supposed to be quick-and-dirty.
- It’s a “roll-under” mechanic, and while this isn’t an issue for many players, I’ve never liked using positive modifiers to make something harder.
Those are my biases laid bare, and they’re not deal-breakers. Of course, there’s nothing wrong with Moldvay’s approach, but I want to offer an alternative that does a bit more heavy lifting without adding overhead.
Revisiting BX Ability Checks
Perhaps not surprisingly, the Basic Rules already offers an elegant solution via the reaction roll tables for NPCs (B21) and monsters (B24). Reaction rolls are made with 2d6 and incorporate the character’s Charisma ability score adjustment,1Note the CHA-based reaction roll adjustment range is -2 (CHA 3) to +2 (CHA 18), though my advice is to use the -3 to +3 range used for all other abilities – it’s consistent and doesn’t upset the roll results. but with a few tweaks, the format can represent any ability check.
Roll 2d6 and modify by the ability score adjustment (-3 to +3); apply and additional ±1 for easy or difficult circumstances:
| 2d6 Roll | Result |
|---|---|
| 2 or less | Failure + Consequences |
| 3-5 | Failure |
| 6-8 | Success + Complications |
| 9-11 | Success |
| 12 or more | Success + Benefits |
Results of “Success” or “Failure” are simple and self-explanatory: the character’s attempt either worked or didn’t work, no muss – no fuss, end of story. But there’s room for special fun:
- Failure + Consequences: The character screwed up royally, not merely failing, but excelling at catastrophe (snapping the rope you’re attempting to climb, or remembering two contradictory clues).
- Success + Complications: The character’s attempt works, but not as effectively as planned (they climb the rope, but weaken it for the next PC, or they remember only part of the clue).
- Success + Benefits: The character doesn’t just succeed – they crush it, gaining some unexpected advantage (they climb the rope fast enough to get an extra action, or they remember the clue along with some extra, obscure and useful knowledge).
Final Words
There’s more mileage to be had out of this approach, like maybe a D&D social mechanic (!) or maybe even the foundation of a skill system (!!). But before lobbing those concepts at your mind-ball, I’ll wait to hear what you think of it in the comments section.
As I noted on Facebook, I’ve seen various iterations of this over the years, using the Rules Cyclopedia reaction roll — yours is a nice and elegant approach, very “PbtA” in the addition of complications or benefits. I would definitely like to see this expanded outward into a skills system.
I’ve used it for a quick and dirty ability check system and it’s worked well when used sparingly. It should not replace player skill. If the players have a plan that is sound and should work, or they are doing something normal like riding a horse, no rolls should be made. The old joke that no characters ever fell off a horse until non-weapon proficiencies were added to the game is true. I had a DM call for rolls on the table for every damn thing we wanted to do and it didn’t feel much like D&D after a while.
Another thing I’ve always thought could work to tie success to character experience is to call for whatever saving throw seems most appropriate for the thing being tried. For some kind of fast action, Breath Weapon might be appropriate. For endurance, a Poison Save would work. For lore/knowledge or to read an old language in the dungeon, a save vs Magic might be the best bet.
It also makes sense to have whatever character is most suited by class try the thing instead of everyone rolling to help protect their niche.
“The old joke that no characters ever fell off a horse until non-weapon proficiencies were added to the game is true.”
Too true, and I agree that ability checks or skill rolls should never replace a player’s description of what their character is doing. It’s the old “candlestick secret door” thing: if the candlestick opens the secret door, and the player says their character is moving the candlestick, the secret door is revealed – no need to roll.
One thing I’ve slowly incorporated is using ability checks and skill rolls less as success/failure and more as clues to the player. So a successful secret door check might mean I tell the player something about the candlestick. A failed roll means a less helpful clue. The die roll suggests how good a nudge I give the player, but ultimately, the action still relies on player description to succeed.
I’m a fan of the 2d6 Reaction roll, and I like the idea for using the same mechanic for ability checks as well! Mmmm…
For a social mechanic, Courtney over at Hack & Slash created the fantastic On The Non-Player Character. It has a social mechanic built precisely around the reaction roll.
Here’s a link: https://www.drivethrurpg.com/product/115917/On-the-Nonplayer-Character
I love Courtney’s stuff, but it’s way too expensive for what it is, particularly since it is often jumbled together and not edited very well (lots of typos, orphans, fragments, column misalignments). Don’t get me wrong: his stuff is well-conceived, borderline genius. but it’s rough around the edges and a bit pricy for my PDF pocketbook. He needs an editor and a 25% cut in price at least.
I like using the following mechanic from cyclopeatron esp with “advanced games” like 1e and OSRIC.
https://cyclopeatron.blogspot.com/2010/07/simple-multi-ability-checks-in-classic.html
This is a good approach mathematically, though I’ve not succeeded in implementing it at the table. I like the approach, but I end up stumbling over assigning a difficulty level as an absolute (e.g., what makes jumping a chasm go from Easy to Standard? Length of the chasm? Wind? Angle? Type of surface?).
How do you handle this?
I wouldn’t say it is quite “standardized”, however I do vaguely gauge things. So opening a lock, for example:
– Normal person (3d6) dex with tools
– Thief (3d6) with improvised tools/ (2d6) with tools and a +1 per 5% lockpick. Locks are weak for the most part purchased from your local village/city market.
– Thief with tools on a lock of a powerful ruler being. (4d6) +1 per 5%.
– Thief with tools on a lock of a powerful ruler being…currently under attack or under active pursuit (5d6) +1 per 5%
– Thief with tooks on a lock of a powerful ruler being…currently under attack or under active pursuit …while suspended from freeclimbing or underwater or something… (6d6)
…now this is super off the cuff and took me longer to write it than to think it. I think I just look at the situation in general and assess how many die to assign. People with percentage abilities get bonuses per 5% of ability…
Ensconced in my houserules wiki for my world: https://wikinotes.presgas.name/dokuwiki/doku.php?id=houserules:skillchecks
I think I don’t attach much absolutes in this, and it helps to assign something that a character wants to do without a “skill”…it was the tool I had when I thought about it at the time.
I like this, but I fear the +1 per %5 could get a bit fiddly.
Yeah, however not everyone is specialized. This covers people not there. Also, just like putting in your “expert treasure finder’s” percentages…you would just put in the bonuses…or not! You could as a blanket rule just throw that out and offer a reduction in dice numbers every so often.
It can be as fiddly as one wants.
That helps. Reminds me a bit of WEG’s d6 mechanic. Your examples make sense, though they’d plague my OCD with potential inconsistencies (did I remember to factor in those crappy thieves’ tools? does picking a lock underwater cancel out those awesome thieves’ tools?). But if you’ve mastered the system to the point where it keeps play moving, that’s probably all that matters.