Quick answer
Four is the standard game, one player at each wind. The League's rules also cover three and two players with the same set, building all four walls and skipping the Charleston. With five or six, four play and the others sit out in turn. After each game the player who was East steps out and the next one waiting comes in, and whoever is sitting out may bet on which player will declare mah jongg, or on a wall game.
Four is the standard game, with four seats, four winds, and a Charleston built around them. The League's rules also cover three and two players, and the big change is that the Charleston goes. With five or six, the extra players sit out in turn, and a role called the bettor gives the player sitting out a stake in every hand. Here is how each count works, and which parts are rules rather than house conventions.
Four, and why four
There are four players, one at each of the four winds, which are East, South, West and North. East deals, play passes to the right, and the deal rotates to the next player when the hand ends. The Charleston is built around four seats, since passing right, across and left only makes sense when there is somebody across from you.
This is also the count the card is written for. The hands assume four players feeding a discard pile and four racks competing for the same tiles, which is why short-handed games change the texture of the game even when they keep every rule intact.
Five or six: somebody bets
A fifth friend is not a problem. With five or six, four play and the rest sit out, but the player sitting out is not idle. They are the bettor, and the role is written into the rules.
After each game the player who just finished in the East seat steps out, and the next player waiting rotates in. Because the order is a fixed rotation, everyone takes a turn sitting out. To decide who sits out first, everyone rolls the dice and the lowest roll sits out.
The bettor watches the Charleston finish, then looks at the racks and privately picks the player they think will declare mah jongg, or bets that nobody will and the hand ends in a wall game. The bet is placed after all Charleston passing is done and before play begins.
What the bettor may and may not do
Silence. The bettor may sit with the table and be sociable, but they cannot advise anyone, point out a missed joker exchange, note an error, or call a hand dead. Any interference voids the bet, which is the whole enforcement mechanism and the reason the role works at all.
If the bettor picked correctly, they collect alongside the winner. When the winner drew their own winning tile, both are paid at the doubled rate, and when the winning tile came off a discard, the discarder pays the higher amount while the rest pay the standard one. If the bettor picked wrong, they pay the winner what their chosen player owed. If they bet on a wall game and no one wins, they collect from each player at the lowest value the current card carries.
Two things follow from that. The bettor has real stakes, which is why sitting out is not a punishment, and the sit-out seat is a good place to learn from, because you are watching four hands develop at once with a reason to pay attention.
Three players
Three works, and the set does not change. Under League rules you build all four walls, deal only to the three seats, and give East fourteen tiles and the others thirteen. Then the Charleston is skipped entirely and East opens with the first discard. Sanctioned tournaments skip it at a three-player table too.
A Charleston at three is a table rule, not part of the League's game. A group that wants one has to settle every detail itself, such as which way each pass goes with no one across, so agree it out loud before the deal rather than halfway through the hand.
Expect more draws each, since three players share a wall built for four.
Two players
Two is covered by the League's rules too. Sit across from each other, build all four walls, deal fourteen to East and thirteen to the other player, skip the Charleston, and East opens with the first discard. If you are playing to practise, a pass of three tiles across is a table rule worth agreeing, because it keeps the decision that shapes every hand.
Each player draws far more often than at a full table, and there is only one opponent's discards to call from, so a direction that needs called sets gets fewer chances at them.
Two-handed play is a poor substitute for a real table and an excellent practice format for reading a deal and naming where it points.
What to agree before you start
If you are four, there is nothing extra to agree, so play the game. If you are five or six, agree that you are using the bettor properly, including the silence rule. Interference voids the bet, and that only works if everyone knows the rule before the hand.
If you are two or three, the League's game has no Charleston. If your group plays one anyway, agree how it works out loud before the deal, and again whenever somebody new joins, so nobody finds out mid-hand that they learned a different house rule.
Put it into practice
New to the game? Start the course at Lesson 1, Meet the Tiles. The first three lessons are free and need no account.
Already play? Have the coach read a real dealt hand for you, free. It names the direction the hand goes for, what to keep, what to pass, and the reasoning behind each call.
Whatever your count, every hand still has to be read. Mei, our AI coach, takes a dealt hand and says which direction it points, what the backup is, and what to pass.