NAGA vs Mortal
If you want an AI to grade your Riichi games, you'll end up choosing between two engines: NAGA and Mortal. One is a polished paid service, the other is free and open source.
The short answer
- You play on Mahjong Soul, or want it free: Mortal, through the free reviewer at mjai.ekyu.moe.
- You play on Tenhou and want several play styles to compare: NAGA.
Side by side
| NAGA | Mortal | |
|---|---|---|
| Made by | Dwango Media Village (Japan) | Equim, an independent developer |
| Price | Paid plans from ¥550 a month (about 10 East–South games) | Free |
| Games it reviews | Tenhou games, plus custom logs in Tenhou format | Mahjong Soul games out of the box on the web reviewer; Tenhou logs with the command-line tool |
| How it works | Neural networks trained on Tenhou's top-table games | Model-free deep reinforcement learning |
| Strength | Says it has reached Tenhou 10 dan | No ladder rank (Tenhou declined an account); beats Akochan in duplicate matches |
| Play styles | Several, from defensive to call-heavy | One |
| Code | Closed | Open source (AGPL-3.0); trained weights not released |
NAGA: the paid specialist
NAGA is the Riichi AI from Dwango, the company behind Niconico. You sign in, paste a Tenhou game, and NAGA marks every discard, call and riichi decision. Its standout feature is multiple play styles: you can see how a defensive NAGA, a call-heavy NAGA and a balanced one would each have played your hand. Plans are paid in points that are spent per analysis. See our NAGA profile for prices and details.
Mortal: the free, open engine
Mortal is the strongest Riichi engine whose code you can read. Its author also runs mjai-reviewer, which reviews your games with Mortal for free. The web version at mjai.ekyu.moe works with Mahjong Soul games without any install. Mortal can't prove its strength on Tenhou's ladder, but in duplicate matches (the same tiles dealt from every seat) it consistently beats Akochan, the previous free standard. See our Mortal profile.
How to use either one well
Whichever you choose, the review is only useful if you read it properly. Our guide on how to review your Riichi games with AI walks through getting your game log and what to look for.
Practise what the review teaches
Reviews tell you what to change; practice makes it stick. Riichi on Mahjong Live is free in your browser against AI opponents, and shows the yaku, han, fu and payments after every win.
Practise Riichi free
Play Riichi against AI opponents in your browser, with every win explained.