Sensei 21 · Blackjack Trainer
A blackjack school for adults
From your first hand to counting cards, one short lesson at a time. Every mistake gets a bonk.
Join the waitlist
Coming soon to iPhone and Android.
Good.
Now practice patience.
You’re on the list.
We’ll email you when Sensei 21 comes out. Until then, follow the build on Instagram: @sensei21app
How the dojo works
One idea per lesson
Three minutes, and you play it at once.
Mistakes get bonked
Then the hand comes back, so you can fix it.
Decisions, not luck
A right move that loses still counts.
A little, every day
A daily streak keeps you sharp.
From egg to black belt
Every belt ends with an exam and a ceremony.
Egg to purple belt. Basic strategy, every hand. Free.
Back Room
Brown and black belt. Card counting. A one-time purchase, no subscription.
A school, not a casino
- No real money. Crumbs come only from right decisions.
- No casino links, no ads, no loot boxes.
- Every answer matches the strategy tables.
Practice only: never use it at a real table. Blackjack keeps a house edge even when you play every hand right.
Who’s building it
I’m David, a DJ from Croatia with 3,000 gigs behind me. I build Sensei 21 with AI tools, and yes, the Sensei bonks me too. Follow the build on Instagram: @sensei21app
Questions
Is it gambling?
No. There is no real money anywhere in the game. You earn crumbs for right decisions, and crumbs can’t be bought or cashed out. There are no casino links, no ads and no loot boxes.
Why is it 18+?
It teaches a casino card game, so it’s made for adults only. The app stores rate games like it 18+ as well.
Do I need to know blackjack already?
No. The first lessons cover what the cards are worth, what you’re trying to do, and what hit and stand mean. You play your first hand in the very first lesson.
Will it help me win at blackjack?
It teaches you the right decision on every hand: the move that loses least over time. Blackjack keeps a house edge even when you play every hand right, and practice results don’t predict casino results.
Sensei 21 is a school, not a way to make money.
Is card counting legal?
Counting cards in your head isn’t a crime in most places, but a casino can still ask you to stop playing or to leave. Using a phone or any other device to count at a casino table is a crime in many places, Nevada among them.
Sensei 21 is for practice only. Never use it at a real table.
What will it cost?
Learning to play every hand right is free: from the egg to the purple belt, with the practice table and the Daily Dojo. Card counting lives in the Back Room, a one-time purchase with no subscription. Nothing else is for sale, and there are no ads.
When does it come out?
There’s no date yet. Testing comes first. Join the waitlist and you’ll hear when it comes out, and, if you like, when testing opens.
How do I become a tester?
Join the waitlist and switch on “Invite me to test it early”. iPhone testers get the test version through TestFlight, Apple’s app for test versions. Android testers get it through Google Play, so join with the email of your Google account.
Who makes Sensei 21, and is AI involved?
One person: me, David, a professional DJ in Croatia. I’m not a programmer, so I build Sensei 21 with AI tools. Claude writes the code from my descriptions and helps with the design documents and text. The pixel art is generated with PixelLab, an AI pixel-art tool, from fixed character references and a strict style guide, and checked against the game’s other sprites before it goes in.
Every strategy answer the Sensei gives matches published basic-strategy tables (all 350 chart cells and all 22 counting deviations), and automated tests keep it that way.
Which rules does the dojo’s table use?
Six decks, the dealer stands on soft 17, you may double any first two cards and after a split, blackjack pays 3 to 2, and the dealer checks for blackjack. Surrender comes later, at the purple belt, for tables that offer it.
The table at the top of this page is a taste of the first belts: Hit or Stand only, so a hand the full chart would double is played as a hit.
Something else? Write to info@sensei21.com, or send a message on Instagram: @sensei21app.
Sit.
Watch the cards.