Menzenchin
For the yaku, see menzen tsumo.
A hand is menzenchin 「門前清」, menzen 「門前」 for short, or "closed" in English, when it has not called on another player's discarded tile. This means the player has not called chii, pon, or an open kan. A closed kan (kan when drawing all 4 tiles yourself) does not break the closed state. Some yaku require the hand to be closed. Certain other yaku lose value when the hand is not closed.
A hand that is not closed is known as an open hand. This would be a hand that has called chii, pon, or an open kan. Conversely, if a hand is open, it cannot score some yaku, and other yaku are reduced in value. While an open hand is usually less valuable than a closed one, it has the ability to use chii and pon to complete faster.
Yaku
Closed Only
These yaku can only be scored closed; they cannot be scored at all with an open hand.
| 1 han | 2 han | 3 han | |
|---|---|---|---|
| Riichi | Iipeikou | Double riichi | Ryanpeikou |
| Ippatsu | Pinfu | Chiitoitsu | |
| Menzen tsumo | |||
Kuisagari
Kuisagari 「喰い下がり」 is a property of some yaku to lose value when called open. Each yaku affected by kuisagari loses 1 han in an open hand.
| From 2 han to 1 han | From 3 han to 2 han | From 6 han to 5 han |
|---|---|---|
| Sanshoku | Honitsu | Chinitsu |
| Ittsu | Junchan | |
| Chanta |
Open
These yaku are unaffected by the hand's open/closed status.
| 1 han | 2 han | ||
|---|---|---|---|
| Tanyao* | Haitei | Sanankou | Shousangen |
| Yakuhai | Houtei | Sanshoku doukou | Toitoi |
| Chankan | Rinshan | Sankantsu | |
* Assuming kuitan (open tanyao) is enabled.
In addition, any yakuman that can be scored open do not lose value if opened.
Strategy
The decision on whether to play open or stay closed on the hand will depend on many factors, including your current hand (value/speed), the current round #, and point standings.
Most importantly, every hand requires at least one yaku to win. Any closed hand can declare riichi for a guaranteed yaku, but an open hand requires at least one other yaku. Therefore, when opening your hand, make sure to plan at least one yaku. The most common open yaku are tanyao (if allowed) and yakuhai. though others can be viable too.
For more details, see naki strategy.