A yaku is a particular hand combination. It is necessary to have at least one yaku in order to win. Yaku can be awarded also on particular situations, not only by hand combination. The value of a Yaku is expressed in Han. They are used used to calculate the score. Having more han will result in bigger score. Is it possible to have more yaku in a hand. In that case the Han value is added up.
When a player has a concealed hand and then draws the winning tile from the wall to complete it.
A Riichi is a special declaration of being in Tenpai that is also a 1 Han Yaku. Any time a hand is concelead and in Tenpai, a Riichi can be declared. To do so, the player says "riichi", places a 1000-point stick on the table as a deposit, and discards its tile sideways. From this point on, the player may not change the content of their hand. They must discard any tile that does not allow them to win. One exception: if the player has a three of a kind and they draw the fourth tile to complete a four of a kind, they may declare a kan as long as it does not change the wait of the hand.
When a player declares riichi and then receives the winning tile within one round of play, or before the round is interrupted by call. The tile can either be a discard from another player or drawn from the wall.
Double Reach is a Reach declared on the first discard (with no Pon, Chi, or Kan before first draw). All Reach rules apply.
Winning on the last legal tile in the wall.
Winning on the last discard of a player.
When a player declares a quad, they must draw a supplemental tile from the dead wall to keep the number of tiles in the hand consistent. If that tile completes the hand, it adds one han to the hand’s value.
A possible rule for this yaku: if the player uses a discard to complete a quad, then completes their hand with a tile from the dead wall, the player who discarded the tile is responsible for paying the entire amount for the hand. The rule is called pao (包).
If a player has an open three of a kind and draws the fourth tile in the set to make a four of a kind, they can add it to the triplet. However, if another player requires that tile to complete their hand, they can Ron with that tile. In this case the win is considered a Ron from the player who declared the Kan.
The discards of a player are all terminals and honours. The round must be a draw. Often recognized only if none of the discards of that player was called. The hand doesn't need to be in tenpai. As for the payment, the hand is regarded as a winning by tsumo. The rule of nou ten bappu is usually not applied to this case.
This is the list of yaku hands ordered by han value. Some hands must be closed to be yaku, some lower their value if are open.
A hand with no terminal and honour tiles, that is every tile in the hand is a suit tile between 2 and 8.
*Open Tanyao is called Kuitan (食いタン / 喰いタン). Some rulesets forbid Kuitan.
Two completely identical sequences in the same suit.
It does not combine with Chiitoitsu.
Any set that includes either a dragon, the player's own wind, or the wind of the round. 1 han for each of these set. (A double wind gives two han, accordingly.)
The same sequence in three suits.
Three sets of same suit: 123, 456, 789.
Every set must have at least one terminal or honour tile, and the pair must be of a terminal or honour tile. Must contain at least one sequence (123 or 789).
All tiles are terminals or honours. (Since this hand will have also Toi Toi or Chiitoitsu, remember to add 2 han for those hands). Chiitoitsu version is called Honroochiitoi.
The hand consists of all threes or fours of a kind (and of course a pair); no sequences.
Note that if this hand is closed, it will also score for Sanankou.
Three threes or fours of a kind, that are entirely drawn from the wall. (The other sets and pair need not to be closed.)
The hand contains three fours of a kind. They can be open or closed. Some rulesets value this hand as 3 Han. Can be combined with Toitoi, San ankou.
Three triplets consisting of the same numbers in all three suits. Some rulesets value this hand as 3 Han.
A hand composed of seven pairs. All pairs must be distinct (that is, four of kind is not considered two pairs)
This is one of the special hand that break the rule of four sets and a pair (other being Kokushimusou).
Two three of a kind of two dragons, plus a pair of the third dragon. (Remember to add 2 han for the 2 Fanpai)
The hand contains tiles from a single suit plus honours.
Every mentsu must have at least one terminal, and the pair must be of terminals. No honours present. Must contain at least one shuntsu (123 or 789).
The hand contains two different Iipeikou's. Must be concealed. Cannot be combined with Chiitoitsu. (Actually the hand value is one han, plus two han from each of the IIpeikou's.)
All tiles are of the same suit.