Riichi Mahjong Rules

The game follows Mahjong Soul's 4-player ranked rules, the most common online riichi ruleset. Where Mahjong Soul's exact behavior wasn't documented, the choice and the reason are noted below.

Setup and scoring

• 4 players, 136 tiles, 3 red fives (one each of 5m, 5p, 5s).
• Start 25,000 points; 30,000 return. Final score = (points − 30,000) / 1000 + uma 15 / 5 / −5 / −15, with +20 oka to first place.
• Ties in placement go to whoever sat closer to the starting dealer.
• Dead wall of 14 tiles. One dora indicator at the start; each kan adds one. Ura dora (one per revealed indicator) count only for riichi winners.
• Open tanyao (kuitan) allowed. Kiriage mangan is not used: 30 fu 4 han is 7,700 and 60 fu 3 han is 7,700 (non-dealer).
• Honba: +300 per counter on ron, +100 from each player on tsumo.
• Fu: 20 base, +10 closed ron, +2 tsumo (not for pinfu tsumo), sets 2/4/8/16/32 by type, value pair 2 each (a double-wind pair is 4), +2 for kanchan, penchan or tanki. Rounded up to 10. Chiitoitsu is a flat 25. An open hand with no fu is 30 on ron.
• Limits: mangan (5 han, or 4 han 40+ fu, or 3 han 70+ fu), haneman 6–7, baiman 8–10, sanbaiman 11–12, kazoe yakuman at 13+.
• Yakuman stack. Double yakuman: 13-sided kokushi, suuankou tanki, junsei chuuren poutou, daisuushii.
• When a hand can be read more than one way, the highest-scoring reading is used.

Game length and ending

• East-only (tonpuusen) or East + South (hanchan), picked per game.
• The dealer keeps the seat (renchan) after a dealer win, when tenpai at an exhaustive draw, or after an abortive draw. Honba goes up by one on renchan or any draw, and resets after a non-dealer win.
• If nobody has 30,000 when the last hand ends, play extends one wind (East-only → South, hanchan → West) and ends as soon as someone has 30,000. The extension ends after its 4th hand regardless.
• Agari-yame / tenpai-yame are automatic: in the last hand, if the dealer wins or is tenpai at the draw while in first with 30,000+, the game ends.
• Busting: the game ends immediately if anyone drops below 0 (0 exactly is fine).
• Riichi sticks left on the table at the end go to first place.

Riichi

• Requires a closed hand (closed kans allowed), tenpai after the discard, 1,000+ points, and at least 4 tiles left in the live wall.
• The 1,000-point stick is paid once the declaration tile passes without a ron. If that tile is ronned, the riichi doesn't count and no stick is paid.
• Double riichi: declared on the first discard with no calls made yet.
• Ippatsu: win before your next discard, broken by any call including a closed kan.
• After riichi you must discard what you draw. A closed kan is allowed only with the tile just drawn, only if it doesn't change your waits, and only if every reading of the hand has that tile as a triplet (no okurikan).

Calls

• Ron beats pon/kan beats chi. Chi only from the player on your left.
• Multiple ron allowed, including triple ron (no sanchahou in Mahjong Soul). Honba and riichi sticks go to the winner closest to the discarder's right.
• Kuikae (swap-calling) is forbidden: after a chi or pon you can't discard the called tile's kind, nor the tile at the other end of a chi sequence (call 4 with 56 → can't discard 4 or 7). A call that would leave no legal discard isn't offered.
• No calls on the last discard (houtei), only ron.
• Kans: closed (ankan), open from a discard (daiminkan), or added to a pon (shouminkan/kakan). A closed kan reveals its dora immediately; an open or added kan reveals it after the replacement draw's discard. If the replacement tile wins (rinshan kaihou), the pending kan dora is revealed first and counts. (Mahjong Soul's exact behavior here wasn't confirmed.)
• Chankan: you can ron a tile added to a pon. A closed kan can be robbed only by kokushi musou.
• A 5th kan isn't possible. If four kans are made by more than one player, the hand is aborted after the 4th kan's discard passes.

Furiten

• Permanent: any of your waits is in your own discard pile (including tiles others called away).
• Temporary: you passed on a tile that completes your hand (even if the hand would have had no yaku). Clears on your next discard.
• Riichi: passing a winning tile after riichi makes you furiten for the rest of the hand.
• Furiten blocks ron only. Tsumo is always allowed.

Draws

• Exhaustive draw: tenpai players split 3,000 from noten players. Tenpai on a tile you hold all 4 of doesn't count.
• Nagashi mangan: all your discards are terminals or honors and none were called. Paid like a tsumo mangan; replaces tenpai payments; riichi sticks stay on the table.
• Abortive draws: kyuushu kyuuhai (9+ different terminals/honors on your first draw, uninterrupted, your choice), suufon renda (same wind discarded by all four on the first go-around), suucha riichi (all four in riichi), suukaikan (four kans by different players).

Pao (liability)

• If you pon/kan the third dragon set (daisangen) or fourth wind set (daisuushii) off someone's discard, that player is liable. On tsumo they pay the whole yakuman. On ron by someone else, they and the discarder split it. Any other yakuman in the hand are paid normally.

Yaku list

1 han: riichi, ippatsu, menzen tsumo, pinfu, tanyao, iipeikou, yakuhai (dragons, seat wind, round wind), haitei, houtei, rinshan kaihou, chankan. 2 han: double riichi, chiitoitsu, sanshoku doujun, ittsu, chanta, toitoi, sanankou, sanshoku doukou, sankantsu, shousangen, honroutou. 3 han: ryanpeikou, junchan, honitsu. 6 han: chinitsu. (*one han less when open.) Yakuman: kokushi musou, suuankou, daisangen, shousuushii, daisuushii, tsuuiisou, chinroutou, ryuuiisou, chuuren poutou, suukantsu, tenhou, chiihou. Renhou isn't used.

Sources

• riichi.wiki pages on Mahjong Soul, multiple ron, sekinin barai, kan dora timing and end-game scenarios (via search results; the site blocks direct fetches).
• EMA Riichi Competition Rules 2016 for kuikae and riichi wall requirements.
• Wikipedia: Japanese mahjong yaku and scoring rules.