How it works
Take away, do not fill in
Karadoku is one rule; the rest of this page follows from it. Reckon on two minutes to read, and one game for it to become obvious.
The grid arrives solved
You are handed a sudoku with exactly one solution and thirty-five visible clues. The empty cells are not waiting for you: they already follow from what is there.
The generator did the thankless work first. For as long as there was a digit its twenty neighbours spelled out on their own, it took that digit out itself — those are the moves nobody would enjoy making. What is left to you already needs thinking about.
The gesture is two beats
Touch a digit: its row, its column, its box and every other cell showing the same digit light up slightly. Swipe it down by more than half a cell, and it comes out.
Two beats, and deliberately so: a swipe that starts on a cell and ends on the same cell is not a decision. Taking a digit out by accident is impossible.
What the game checks
The moment you take a digit out, the game counts the solutions of the grid that remains. It stops at two: the only two answers it cares about are “one” and “more than one”.
If it finds one, the cell opens and the light comes through. If it finds two, the digit comes back and the cell is sealed for good. The whole thing happens under your thumb, in a few milliseconds, without asking the network anything.
A sealed cell does not come back
It is the one irreversible thing in the game, and it is painted like it: absolute black, white digit, hatching. Nothing else on screen is that loud.
It costs you nothing you had already opened. It takes away one of the cells you had left to open — the ceiling drops, the score stays.
The score, and when to put it down
Your score is the number of cells you have opened. It never goes down. You bank when you decide to, and the game stops there.
Nothing forces you and nothing stops you: there is no clock, no lives, no game over. Carrying on is always possible, and always a bet.
The highlights deduce nothing
Discovery mode lights up the row, the column and the box you are looking at, along with every cell showing the same digit. That is layout applied to what is already on screen.
The game never shows a cell’s candidates, how many there are, a safety indicator or a preview of the result. It would be doing the deduction for you, and all that would be left is tapping the marked cells.
The daily grid
One grid a day, the same for everyone, worked out from the date by a random-number generator written into the game. No server hands it out.
The result shares as a single line: how many cells came out, against a floor of seventeen. What never gets shared is the shape of the grid — the pattern of hollowed cells is the solution to the problem, and publishing it would spoil the game for everyone who has not played yet.
The most useful advice: when nothing comes out obviously any more, bank. A score you have put down beats a cell you have lost.
A grid is waiting
Take one out, see whether the light comes through.
The game opens in the browser. There is nothing to install and nothing to sign up for.