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Supported Mahjong Games

Mahjax currently implements 4-player Japanese Riichi Mahjong variants. To get familiar with the basic rules, please refer to the official rulebook: European Riichi Mahjong Rules (2016, EN).

While different variants require different strategies due to their specific rules, we believe the core skills they demand are the same:

  • Efficient tile and hand evaluation (reasonable combination calculation)
  • Risk management (defense vs. attack)
  • Reading and inferring opponents’ hands

At the moment, Mahjax provides only No red (aka no red dora) variant.

The “red” in red mahjong refers to additional dora tiles assigned to 5 tiles (usually 5m, 5p, 5s). This has a large impact on strategy:

  • In no red mahjong, players must rely more on yaku (hand patterns) to increase score.
  • In red mahjong, players prioritize efficiency to complete a winning hand quickly and must pay closer attention to risk, as the average hand value is higher and the chance of dealing into a high-value RON increases.

No Red Mahjong

Although no red dora rules are not as popular in the gaming industry or in existing Mahjong AI research, they are widely played in Japan. Some professional leagues adopting this style include:

These rules emphasize careful yaku construction and more traditional scoring without the volatility introduced by red dora.

Red Mahjong

Red mahjong, especially the rule set used by Tenhou, is currently the most popular variant both in AI research and in commercial online games. We are intended to include this rule in a near furture.

Research Projects Using/Targeting Red Rules

  • Suphx: First top-player level mahjong agent trained by Deep RL.
  • Mjx: C++ based simulator for tenhou rule.
  • Mortal: Rust-based simulator + agent traning code. They also provides the reviewer by their trained agent.
  • NAGA: Agent reached 10-dan in tenhou. They also provide a service to review the playlog by the agent.

Games Using/Supporting Red Rules

These environments typically feature fast-paced play and high average hand values, making them attractive both for players and for AI research.

Future Pathways

Planned future extensions for Mahjax include:

  • Support tenhou rule (Most prioritized).
  • Supporting additional 4-player Japanese Riichi Mahjong rule sets
  • Integrating 3-player Japanese Mahjong rules

These expansions aim to make Mahjax a more comprehensive platform for both Mahjong AI research and gameplay experimentation.