What a d2 is for
- A coin flip. Call 1 for heads and 2 for tails, or the other way round, before the roll.
- Yes or no. Does the guard notice? Is the bridge still standing? When nobody at the table knows, let the coin decide.
- Splitting two ways. Which of two doors, which of two players, which half of the party the ogre goes for.
- 1d2 in the rules. Older editions and Pathfinder use 1d2 for the smallest damage, such as a Small character's unarmed strike.
Rolling a d2 without one
Nobody sells a two-sided die, so the rules have always faked it. The usual way is to roll any die and call odd 1 and even 2. This page skips that and flips a real coin with a 1 and a 2 on it.
Is it fair?
Each face comes up one time in two. The number comes from your browser's cryptographic random generator, not from how the coin tumbles. Flip ten at once and count them: a run of five 2s in a row happens about one time in sixteen, so it will turn up more often than it feels like it should.