Japanese mahjong

Players can make a meld (open group) by calling for another player's discard. They reveal the meld on the table and then make their own discard. Calling for another player's discard makes the group and the hand open. When a winning tile of a closed hand is a discard, the group including that discard is also considered open, while the hand is still regarded as closed. The calls operate exactly the same as any variation of mahjong, except Japanese terminology is used.

Players can make an open sequential group, a sequence (3 consecutive tiles in the same suit), by calling out "chii" (吃 or チー) using a tile discarded by the left player, who is prior in order. Players place the meld face up on the table, usually on the right side of their hands, with the discard placed sideways at the leftmost position of the meld to indicate which tile was taken from the left's discard pile.

Players can make an open identical group, a triplet (3 identical tiles in the same suit, or 3 identical honor tiles) by calling out "pon" (碰 or ポン) using a tile discarded by any other player. Players place the meld face up on the table with one of those tiles placed sideways to indicate from whom the discard was taken.

Players can make a meld from 4 identical tiles in the same suit or 4 identical honor tiles. After calling a quad, the next adjacent dora indicator tile is flipped, and players need to draw a supplemental tile from the end of the dead wall. Depending on the rules, the number of tiles in the dead wall is kept at 14 by reserving the last available tile from the wall, or the number decreases at that time. There are three types of quads. Players call out "kan" (槓 or カン) for all of them.

• Closed quad: Players can make a closed quad if they have four of the same tile in their hand. They reveal those tiles, then place them to the right side of their hand with two tiles face up and two face down. They then draw another tile from the dead wall. A closed quad does not use another player's discard and does not open their hand.
• Open quad: Players can make an open quad using another player's discarded tile if they have three of that same tile in their hand. They reveal the meld on the table with all four tiles face up, with one placed sideways to indicate from whom the discard was taken. Players cannot make this type of quad using an open meld of three tiles.
• Added open quad: Players can make an added open quad (kakan; 加槓) by adding a self-drawn tile or a tile already in their hand to an open meld of the same three tiles.[8] The tile is usually added sideways on top of the sideways tile in the open meld.

The order of precedence to pick up a discard when two or more players want it is ron (winning) first, kan or pon second, and chii third. Kan and pon cannot happen at the same time since there are only four of each tile. Depending on the ruleset being used, these calls may be allowed when the next player has already drawn and seen their next tile. In such cases, that player takes first precedence if they call tsumo.

Yaku are specific combinations of tiles or conditions that yield the value of hands. Unlike many variants, a winning hand consists of four melds and requires at least one yaku. When scoring, each yaku has its own han value, and the han works as a doubler. A winning hand needs at least one yaku. Yakuman is a value for limit hands which are hard to get, and in some variations cumulative and/or multiple yakuman can be counted. Yakuman-class hands ignore all other scoring patterns and points.

Declaring riichi means declaring a ready hand, and is a kind of yaku. A player may declare ready if a player's hand needs only one tile to complete a legal hand (tenpai), and the player has not claimed another players' discards to make open melds. When declaring ready, a player can win on a discard even when the hand didn't have a yaku because ready itself is a yaku.[9] Upon declaring ready, the player must pay a deposit and may no longer change their hand except when forming certain closed quads.

As a possible house rule, a player can choose to reveal their hand to win more points if successful, which is called ōpun riichi (open riichi). In that case, the player shows only the tiles that are related to waits, or reveals all the tiles in the hand depending on the rules.[10] The declaration increases the yaku count allowing the player to score extra points.

Dora (ドラ) are bonus tiles that add han value to a winning hand. Every kind of tile can become a dora tile. A dora tile adds the same number of han value as the amount of its corresponding "dora indicator" tiles. Dora is not counted as yaku, and having it without yaku does not meet the one yaku requirement for a winning hand.[11]

At the start of a hand, the upper tile from the third stack of back end of the dead wall is flipped and becomes a dora indicator.[12] Then, its succeeding tile is recognized as dora. For example, if an indicator is a Green dragon (), Red dragons () are counted as dora by the sequence shown below, in which the Red dragon wraps around to the White dragon ().

The succeeding order of dora is as follows:

---------

---------

---------

----

---

The number of dora indicators increases in the following manner: Each time a player calls a quad, the next adjacent dora indicator tile is flipped, starting with the upper tile from the fourth stack from the back end. The indicator is flipped immediately after the quad is called, and after that the player draws a supplemental tile for their hand from the back end of the dead wall. The number of indicators increases in that direction, which becomes five if a single player calls four quads, and that is the largest possible number from the upper tiles in the third to seventh stacks of the dead wall (see four quads).

In addition, when a player goes out with a declaration of riichi (ready hand), the tiles underneath the dora indicators are flipped after the win and become additional dora indicators, making their succeeding tiles also counted as dora which are called ura-dora (裏ドラ, hidden dora).

It is said that the name dora stands for "dragon," although it has nothing to do with dragon tiles in contemporary Japanese mahjong.

• Red 5 tiles: A variation uses specially marked red number 5 tiles that also count as dora themselves, regardless of dora indicators. In addition, if a dora indicator is number 4 of the same suit as red 5 tiles, players acquire further han value. One red 5 tile for each suit is usually used in place of regular five tiles, with some local variants using various amounts (two 5-pin only, two 5-pin and one 5-sō and 5-wan, two of each 5 in all three suits, et cetera). In some variations, tiles of other numbers such as 3 or 7 can be marked red.[11]

Among the mahjong variants, the Japanese scoring system is unique. Two variables are considered: the han value and fu value. A hand winner acquires points based on these values, which correspond to a points-value table. If the han value is five or more, then the fu value is still counted but no longer necessary.

There is a distinction between winning from the wall and winning from a discard. When going out, players call out "tsumo" (自摸 or ツモ, self-drawn) or "ron" (栄 or ロン, picking up a discard). In the case of tsumo, the other three players share the responsibility of paying out points, according to the scoring table. For ron, the player who discarded the tile pays all of the points.

In many mahjong variants, discards are simply placed in the middle of the table in a disorganized fashion. However, with the Japanese variant, tiles are neatly placed in order of discard in front of each player. In turn, each player accumulates a discard pile, with each hand. Typically, discards are placed in rows of 6 tiles as per customary rule. In addition, open calls for chii, pon, and kan have discard specific rules, by which they must indicate the source and type of discarded tile. This way, a record is maintained for all discarded tiles corresponding to each player. Likewise, game strategy depends on the state of the discards and the players' hands.

In the sacred discard rules, which are also called furiten (振聴 or フリテン), there are three situations in which a win using another player's discard is forbidden:[13]

1. A player cannot win on any discard if any of their potential winning tiles are present in their discard pile.[14] This includes tiles that have been called by other players for open melds.[15]
2. If a winning tile is discarded and the player does not call it to win, that player cannot win on any discard after it until their next turn. This is known as "temporary furiten". This applies even if that winning tile could not have been called for the win due to the resulting hand having no yaku. Generally, other players making open melds does not end temporary furiten.[16]
3. Temporary furiten is permanent after riichi - If a player passes on a winning discard after declaring riichi, that player can no longer win on any discard.

In Japanese mahjong, many rules allow abortive draws to be declared while tiles are still available. They can be declared under the following conditions:

• Kyūshu kyūhai (九種九牌), shortened from kyūshu yaochūhai tōhai (九種么九牌倒牌): On a player's first turn when no meld has been called, if a player has nine different terminal (also known as major[17]) or honor tiles, the player may declare the hand to be drawn. For example, the hand may be . They could instead go for the thirteen orphans (kokushi musō) hand.
• Four winds' barrier (四風子連打, Sūfontsu rendā): On the first turn without any meld calls, if all four players discard the same Wind tile, the hand is drawn.
• Sūcha riichi (四家立直), or Yonin riichi (四人立直): If all four players declare riichi, the hand is drawn after the last player discards without dealing in.
• Four quads abort (四槓散了, Sūkan sanra): The hand is drawn when a winning hand cannot be made from the discard after the fourth quad is called, unless all the four quads were called by a single player. If the four quads were collectively called by two or more players, the game may end upon the last player to make a quad discarding (either safely or dealing in), or it may end immediately. If all four quads were called by a single player, the hand continues. Once four quads have been made and the game is allowed to continue, generally, a fifth quad is unable to be formed. Like most optional settings, it is possible that a local mechanism is in place to allow for further quads, but is very rare.

Players may be penalized under the following circumstances:

• Gotsumo. Calling tsumo with an invalid hand
• Furiten ron. Calling ron while furiten
• Noten riichi. Calling riichi while not in tenpai
• Machi ga kawaru riichi-go no kan (待ちが変わるリーチ後のカン) Closed kan after riichi if the kan changes the player's waits
• Tāhai (多牌). Having more tiles than allowed (depending on the rules)[18]
• Yamakuzure (山崩れ). Literally 'landslide'. Damaging the wall to the point that it cannot be recovered[18]

A game ends when a player's score becomes negative (below zero), or in some rare local rules, at zero points or less. Some rules may allow continued gameplay with a player having a negative point value.

Some rule sets allow for the last dealer to decide whether to continue playing extra hands in the final round or stop. A runaway victory (agari-yame, あがりやめ, "win and stop") is when the last dealer decides to exercise this option after winning a hand, for instance when they are the top player at the time.[19] In some cases, a stop may be allowed simply for playing a hand and ending with a ready hand (tenpai-yame, 聴牌やめ), or in very rare cases, allow the last dealer to end the game regardless of position.

If the score of the top player is less than 30,000 points after the last hand of the last round, the game continues into the West round (西場) in some rules. This situation is called shānyū (西入; entering West). The prevailing wind becomes West. A North round (北場) may come next in the same way. Depending on the rules, it can be followed by an East round again or instead White dragon, Green dragon, Red dragon and East rounds.[19] Any extra round ends as soon as one player has 30,000 points or more.

At the end of a match, players are often given bonus points or penalties depending on their placement (see final points and place).

In Japanese Mahjong the first player to complete their hand wins the round. As a result, it is typically advantageous for players to reach a complete hand as fast as possible.

Tile efficiency, also known as tile acceptance theory, is a concept to estimate which tile is best to discard. The goal is to move to a completed hand as fast as possible, aided by maximizing the number of available tiles that improve the hand

Discards should aim to reduce the shanten (向聴) of the hand, the number of tiles required to reach a ready hand (tenpai). As a consequence, discards should also aim to increase the ukeire (受け入れ) of the hand, the number of tiles that can be drawn to reduce shanten.

Unlike some other mahjong variants, in Japanese Mahjong the player who deals in pays the full point value of the winning player's hand. Defense revolves around avoiding dealing into a player with a tenpai hand.

The sacred discard rules (furiten) can be used to identify safe tiles known as genbutsu (現物). Both the contents and order of tiles in a player's discard pile can be further used to identify tiles that are either statistically unlikely or impossible to be one of their winning tiles.

Push-fold decisions revolve around using tile acceptance and defensive information to weigh whether a player should pursue a winning hand at the risk of dealing in, against abandoning completing their hand in order to discard the tiles least likely to deal in.

Push-fold lies on a spectrum of decisions including betaori (ベタ降り), the complete abandonment of winning in order to avoid dealing in to a tenpai player; zentsuppa (全ツッパ), conversely aiming to complete one's hand without regard to the risk their discarded tiles may pose; and mawashi (回し打ち), stepping back in shanten to avoid dealing in while still leaving open the opportunity to win the hand.