The short version
- Free browser-based Japanese Riichi Mahjong probability simulator hosted at `tenhou-sim.pages.dev` by indie creator Ron.
- Simulates drawing a dealer's initial 14-tile starting hand over and over until you hit Tenhou (Blessing of Heaven / 天和), a yakuman occurring roughly once every 330,000 hands.
- Tracks your cumulative trial count alongside other rare opening patterns (such as Kokushi Musou / Thirteen Orphans, Chuuren Poutou, and Suuankou) on the way to Tenhou.
- Runs instantly on smartphone and desktop browsers via Cloudflare Pages with zero registration or downloads.
At a glance
| Title | Tenhou Simulator (🀄天和シミュレーター🀄) |
|---|---|
| Creator | Ron (tenhou-sim.pages.dev) |
| Target event | Tenhou yakuman (complete 14-tile hand on deal, ~1/330,530 odds) |
| Hosting | Cloudflare Pages (tenhou-sim.pages.dev) |
| Platform & cost | Mobile & desktop browser — Free, no sign-up |
| Category | Web Games |
| Creator / publisher | ろん |
| Official link | tenhou-sim.pages.dev ↗ |
| Heat | 🔥 573 Heat |
| Announced | |
| Data updated |
Why almost no mahjong player sees a real Tenhou in a lifetime
In Japanese Riichi Mahjong, Tenhou ('Blessing of Heaven') is awarded when the dealer's initial 14-tile draw is already a complete winning hand before a single discard is made. Mathematically, the probability of drawing a valid winning 14-tile pattern off the wall is roughly 1 in 330,530.
Even an avid player who sits as dealer 2,000 times a year would need more than 160 years on average to witness a single natural Tenhou at a real table—which is why developer Ron built `tenhou-sim.pages.dev` so players can brute-force the miracle in their browser.
High-speed auto-dealing and trial counter
Instead of playing out full mahjong rounds, the Tenhou Simulator strips the experience down to the opening 14-tile deal. You can draw hands manually or let the simulator cycle through random 136-tile wall shuffles at high speed while watching the trial counter climb.
Whether you get lucky and hit Tenhou in under 20,000 draws or watch the counter roll past 500,000 dry deals, the tool makes the true scale of yakuman probability tangible in seconds.
Instant browser execution on mobile and PC
Deployed on Cloudflare Pages (`tenhou-sim.pages.dev`), all tile shuffling and hand evaluation run locally in your browser with zero lag, no account wall, and an upcoming leaderboard feature planned by the author.
How to try it
Open tenhou-sim.pages.dev in your browser
Click the launch button above to open the simulator on any smartphone or desktop browser.
Start dealing 14-tile opening hands
Trigger single deals or continuous high-speed auto-drawing to search for a complete first-turn winning hand.
See how many draws your Tenhou took
When a completed 14-tile Tenhou hand lands, check your total draw count against the 1-in-330,000 theoretical average.
FAQ
Where can I play the Tenhou Simulator?
Click the launch button on this page to open `tenhou-sim.pages.dev` directly in your mobile or desktop browser.
What are the real odds of Tenhou in Riichi Mahjong?
The theoretical probability of the dealer drawing a complete 14-tile winning hand on the initial deal is approximately 1 in 330,530.
Is the simulator free to use?
Yes, it is completely free and runs in the browser with no registration or download.
