If a character attempts something where the outcome is uncertain and failure has consequences, they make a saving throw, or “save”.
If the Difficulty Check (DC) is specified for the save in question, then use that number. Otherwise, to make a saving throw, add the bonus of the relevant ability to a d20. If the total is greater than 15, the character succeeds. If not, they fail.
If the save is opposed by a foe or another character, each side rolls a (d20) and must get a total greater than the opponent’s roll to succeed. If they fail, the opposing side succeeds. This type of save is called an opposed save. If they hit the same number repeat until one side wins.
If there are situational factors that make a saving significantly easier or harder, the Guide Manager (GM) may grant the roll advantage or disadvantage. If a roll has an advantage, roll 2d20 and use the better of the two dice. If it has a disadvantage, roll 2d20 and use the worst of the two dice.
Designer’s Note: The GM (referee) is of course free to impose positive or negative modifiers rather than use the advantage system, but most players seem to enjoy it and it simplifies the math.
Above Parts modified from: KNAVE which is a rules toolkit created by Ben Milton for running old school fantasy RPGs without classes. Adding, subtracting, and modifying rules is both expected and encouraged.