Kosumi
App Store
The game of Go, for iPhone
Learn Go.
Then play the world.
Kosumi takes you from your very first stone to rated games online. Two-minute lessons, a daily problem, friendly bots that play like real people — and a coach that tells you, in plain words, what happened in every game.
Learn
From the rules to your first win, one step at a time.
A winding path of short, hands-on lessons. The board only accepts the right move — get it wrong and you'll see why. Every unit ends with a bot to beat, so what you learn turns into games you win.
Daily problems
Black to live.
A fresh set every day, matched to your level — classic problems and positions checked by KataGo. Miss one and it comes back in a few days, until it sticks.
Spaced repetition · 3 free a day
Streak & daily goal
12-day streak
- M
- T
- W
- T
- F
- S
- S
Five minutes a day is enough. Pick your goal; Kosumi keeps count.
- 1BasicsLiberties, capture, atari, ko
- 2CapturingLadder, net, snapback
- 3Life & deathEyes, killing shapes, seki
- 4TerritoryBorders, counting, both rulesets
- 5First 9×9 gamesOpenings, cuts, your first bot win
- 6Going 19×19Corners, joseki, direction of play
- 7IntermediateTesuji, shape, endgame, reading
Play the AI
An opponent your size. Always awake.
Kosumi's bots use KataGo's human-style network, trained to play like real players of a given rank. They make the mistakes people make — not brilliant moves followed by baffling blunders. And they run entirely on your iPhone, offline.
- 30 kyu to 9 danplus a professional-level bot and full-strength KataGo.
- 9×9, 13×13, 19×19Handicap stones and komi set for you.
- Learn as you playHints and takebacks when you want them, off when you don't.
- No signal neededPlanes, trains, the middle of nowhere.
Choose your opponent
Reads simple fights well and punishes loose shape. A good target after a few months.
The coach
Every game, explained.
After each game, KataGo replays it move by move. You get the win-rate graph, the handful of moves that really decided it, the better line to play through — and a short explanation in plain language, pitched at your level.
You played C7Better F6
The white stone on F5 had a single liberty left, at F6. Taking it there was worth about five points and made your centre solid. After C7, White connects and your three stones are split.
You played G7Better E4
White's last move threatened to cut at E4, between your D4 and E3 stones. Connecting there keeps one strong group. After G7, White cuts and both halves have to run.
You played B2Better H5
B2 secures a point or two in a corner that was already yours. The open right side was worth far more: H5 builds territory and keeps White's wall from growing.
The explanation only describes what KataGo found — position, best move, the line that follows, points lost — so it never makes up Go.
Play online
Rated games, whenever you're ready.
Pick a format and get matched with someone near your level. Your rating shows as kyu and dan, per board size, and it starts from how you did in lessons and against the bots — not from zero.
- 9×9
Blitz
3 min + 3 × 10 s
- 9×9
Rapid
5 min + 3 × 20 s
- 13×13
Rapid
10 min + 3 × 30 s
- 19×19
Rapid
20 min + 5 × 30 s
- 19×19
Live
10 min + 3 × 30 s
- Any size
Correspondence
1 or 3 days a move, with a nudge when it's your turn
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Your rules
Japanese (territory) or Chinese (area) scoring. Dead stones are marked for you at the end; you confirm.
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Friend codes
Share a code or a link and play a friend in any format, rated or just for fun.
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Never wait long
If nobody's free in about 20 seconds, Kosumi offers a bot at your rating — clearly labelled, and never rated.
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Fair play
Every move and clock is checked on the server. Engine help in rated games gets accounts banned.
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Honest ratings
Glicko-2 per board size, shown as kyu and dan. Provisional for your first ten games.
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Friendly by design
Chat uses preset phrases — "Good luck", "Nice move", "Thanks for the game". Report and block are one tap away.
Pricing
Free to learn. Premium to go further.
The whole beginner course and unlimited games cost nothing. Premium opens every lesson and the full coach.
Free
- Beginner lessons, units 1–5
- 3 problems a day
- Unlimited games against the AI
- Unlimited rated games online
- 1 full game review a day
Kosumi Premium
About $3.33 a month — or $4.99 billed monthly.
- Every lesson, up to intermediate
- Unlimited problems with spaced repetition
- Unlimited game reviews
- Coach explanations and hints, as many as you like
- No ads, ever — same as free
Auto-renewing subscription, cancel anytime in your Apple ID settings. Free trial on the yearly plan. Prices in USD; local pricing set by the App Store.
FAQ
Questions, answered.
Is it really free?
Yes. The full beginner course (units 1–5, from the rules to your first 9×9 wins), three problems a day, unlimited games against the AI, unlimited online games and one full game review a day are free, with no ads. Premium adds every lesson, unlimited problems and reviews, and the coach's explanations and hints.
What is KataGo?
KataGo is an open-source Go program and one of the strongest in the world, far beyond any human professional. Kosumi runs it on your iPhone to power the bots and the game reviews, using its human-style network, which is trained to play like a person of a chosen rank.
Does the AI need an internet connection?
No. The bots and KataGo's analysis run on your iPhone, so you can play and review offline. You only need a connection for online games, syncing your progress and the coach's written explanations.
Which rules does Kosumi use?
Your choice, game by game: Japanese rules (territory scoring) or Chinese rules (area scoring). At the end, Kosumi marks the dead stones and counts; you check and confirm. The lessons explain both.
I've never played Go. Is this for me?
It's built for you. The first lesson starts with placing a single stone. Lessons take about two minutes each on small 5×5 and 7×7 boards, and by the end of unit 5 you'll be playing — and beating — your first bot on 9×9.
Which languages are available?
English, French, German, Spanish, Italian, Dutch, Japanese, Korean and Chinese (Simplified). Go terms are translated properly — atari, アタリ, 단수, 打吃 — and the coach explains in your language.
How do I cancel Premium?
In Settings on your iPhone: tap your name, then Subscriptions, then Kosumi. Cancel at least 24 hours before the end of your trial or billing period and you won't be charged again.
Is Go the same as baduk and weiqi?
Yes. Go is called igo in Japan, baduk in Korea and weiqi in China — the same 4,000-year-old game of black and white stones.