Rules as Interfaces Redux


(approx. 700 words)

This post originally appeared on the Pen and Paper Games Forum. Only some markup (markdown) has changed.

Yesterday I babbled about viewing RPG rules as an interface between players and GMs, similar to a GUI or API in computer programs. In this view, the game rules, like GUIs or APIs, are most useful when they avoid unnecessary clutter and complexity.

One other interesting consequence of this analogy is that, like interfaces, rules have to be stable in order to be useful. This applies both to official versions of the rules and house rules.

For example, in every version of D&D combat requires rolling 1d20 at or above a certain target number … but there the resemblance ends. Early versions used disjointed and ad-hoc procedures to resolve other events: Thieves who plied their craft rolled level-based target numbers on percentile dice or 1d6 rolls (sometimes both in the same version), Fighters rolled on a different Strength-based percentile table for feats of strength, other characters roll their base characteristics or lower as the DM decides. 3.x introduced skills, ascending AC, and Attack Bonuses so that all but damage requires 1d20 + bonuses against a Target Number (like Armor Class) … but the number of bonuses under each situation proliferated enormously; 4th edition simplified the number of skills and types of attack rolls to the point of blandness. Mutants and Masterminds and True 20 eliminates random characteristics, hit points, and damage rolls so that players only needed a d20, while Dungeon Crawl Classics gives characters “action dice” and variable bonuses which can vary from a d8 (for a first-level thief reading a spell scroll) to a d20 + d10 + 4 (for a top-level fighter’s first two attacks).

Contrast that to RuneQuest, nearly as old as D&D, which made everything a percentile roll, either as a straight percentile skill or a contest between characteristics on a Resistance Table which basically boils down to 50% + (Active_Characteristic - Resisting_Characteristic) x 5%. The names and meanings of skills have changed from version to version, and across descendants like Basic Roleplaying, Call of Cthulhu, Legend, OpenQuest, Stormbringer, and Worlds of Wonder; direct contests between skills have replaced the Resistance Table in modern versions of RuneQuest. Still, when players must meet a challenge they know to grab their percentile dice and look for the relevant skill or characteristic.

And that’s just dice rolling conventions. Add in magic, special powers, tactical combat maneuvers, technology, and requirements of genre emulation and the number of rules can grow enormously. Modern games, however, home in on a “core mechanic” to resolve any possible conflict, then build out from there to cover combat and other special circumstances. Some like FATE, HeroQuest, or Numenera go one step further: even these special circumstances boil down to a simpler mechanic, like Aspects and Stunts, extended contests, or negotiating a Difficulty Level.

Reducing the number of rules needed at the table speeds play. The best GM I’ve yet to play with decided to run D&D 3.5 “by the book” for a few sessions. (He was preparing to run a tournament game.) My character’s idea to carve wooden spears lead to a 15 minute rules delve and a bit of arithmetic just to determine how many spears he could carve in the time available. If the 3.5 rulebook had been smaller that could have been two minutes or a quick decision (e.g. “five”).

Like a computer interface, then, the best RPG rules are no larger than they need to be, versatile enough to cover any situation, and sufficiently well-understood so that users don’t get confused or frustrated. The computer world evolved graphical conventions, languages, and manuals so that (theoretically) novice users can concentrate on their tasks, not the mechanics. In the RPG world players typically have only a character sheet, dice, written rules (maybe), and the GM; by and large players want an adventure or a collaborative story, not a test in math and reading comprehension.