Optional rule

An optional rule is a rule that is provided in the text of a role-playing game (either a rulebook or a supplement), but which is explicitly not part of the core rules of the game and is instead included only as an option for groups to include if they want to.

Examples of ways that an optional rule may originate include:

• an ascended house rule that was widespread enough to be incorporated into an actual rulebook (such as rules for critical failures in the Dungeons & Dragons 3rd edition Dungeon Master's Guide),
• a holdover from previous editions or expectations of a game that have not been entirely removed, or
• rules that pertain to a specific play style that not all groups may use (such as rules for miniatures combat that will only be useful for groups that play with miniatures, e.g. flanking in Dungeons & Dragons 5th edition).

Role-playing game criticism sometimes considers optional rules as being just as important to the understanding of a game as its core mechanics. Levi Kornelsen has said that, although common, this requires an assumption that game groups are incapable of eliding and ignoring parts of a game that they don't need.