American Mahjong, live, with friends.
OpenMahj is a free, browser-based multiplayer game for four players, built around NMJL-style American Mahjong: the Charleston, discards and calls, and a hand you race to complete. Create a room, share the code, and play — no account, no download.
No sign-up. No install. Open source.
Your hand, exactly as it renders at the table.
What is OpenMahj?
OpenMahj is a real-time, four-player online adaptation of American Mahjong in the NMJL style. A server referee holds the wall and every player's hand, validates each Charleston pass, discard, call, and Mah Jongg claim, and sends each player only what they're allowed to see. There's no app to install and nothing to configure — a room code is the entire setup.
How a hand works
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Create or join
Pick a display name, then create a room or enter a 4-character code to join one.
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Charleston
Pass three tiles at a time in the opening exchange to reshape your hand.
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Draw, discard, call
Take turns drawing and discarding; call Pung, Kong, or Quint when your hand allows it.
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Declare Mah Jongg
Match a pattern on the active card and declare — the server validates and scores it.
Built for a real game night
Real-time, server-validated play
Every discard, call, and claim is checked by the server before anyone sees it — no relying on the honor system.
No accounts, ever
Pick a name, share a room code, and you're at the table. Nothing to remember between sessions.
Bots fill empty seats
Short a player? A rule-based bot takes the seat so the game starts and keeps moving.
Reconnect anywhere
Lose signal or close the tab? Reopen the same room link and resume your seat with your hand intact.
Table chat
Talk through the hand without leaving the app — chat is scoped to your room.
Bring your own hand card
Hand patterns load from a JSON file you supply — your own transcription or a house-rule card — since the official NMJL card is copyrighted and isn't shipped with OpenMahj.
Frequently asked questions
Is OpenMahj free to play?
Yes. OpenMahj is free to play and open source, with no accounts and no paywalls.
Do I need to create an account?
No. Pick a display name, then create or join a room with a 4-character code — that's the whole sign-in flow.
What Mahjong ruleset does OpenMahj use?
OpenMahj follows NMJL-style American Mahjong: a 152-tile set with jokers and flowers, a Charleston passing phase, and hands defined by a hand card.
Does OpenMahj include the official NMJL card?
No. The NMJL card is copyrighted and sold separately. OpenMahj reads hand patterns from a JSON file you provide — your own transcription or a house-rule card — instead of shipping the official card text.
Can I play with fewer than 4 people?
Yes. Any empty seat is filled by a rule-based bot, which hands control back if the missing player joins later.
What happens if I lose connection mid-game?
A bot takes your seat after a short grace period. Reopen the same room link and you resume control with your hand exactly as you left it.
What devices does OpenMahj work on?
Any modern browser on phone, tablet, or desktop. The table layout adapts fluidly to the screen it's running on.