What is Ura Dora in Riichi Mahjong? (Hidden Bonus Tiles)
Ura dora is the hidden upside of declaring riichi. Win, flip the dora indicators over, and every matching tile in your hand turns into another han.
What is ura dora?
Ura dora (裏ドラ, "underside dora") are bonus tiles indicated by the tiles sitting underneath the regular dora indicators in the dead wall. They are face-down and unknown for the entire hand — until the moment of a riichi win, when they are flipped over and counted.
When are ura dora revealed?
Only when the player who declared riichi actually wins the hand. The dealer (or whoever is closest to the dead wall) flips the tiles directly under every active dora indicator. Lose or draw the hand, and the ura indicators stay buried — you never even learn what they were.
How do ura dora score?
Each ura indicator points at the same "next tile" pattern as a regular dora indicator: an indicator showing 3m makes 4m the ura dora, indicator 9p makes 1p the ura dora, indicator East (1z) makes South (2z) the ura dora, etc. Every matching tile in the winning hand adds 1 han. Two 4m plus an ura indicator of 3m is +2 han.
Why are ura dora tied to riichi?
It is the system's reward for committing to a closed, locked hand. Riichi already costs 1,000 points and surrenders defensive flexibility; ura dora compensates with an expected ~0.6 extra han per riichi win on average. Together with the riichi 1 han and the chance of ippatsu, this is what makes riichi the highest-EV declaration in riichi mahjong.
Are ura dora a yaku?
No — ura dora is a han bonus, not a yaku, exactly like regular dora and aka dora. It needs a separate yaku (almost always riichi itself) to make the hand valid. Once a win is locked, ura dora can swing the score one or two han, lifting a mangan into haneman or a haneman into baiman.