Nine Apart
No guessing, and no pen-or-pencil button. What is in a square already says what it is.
What it is
Sudoku. Nine rows, nine columns, nine boxes, each holding one to nine once. No download, no account, nothing timed against you.
Three promises, not two
Exactly one answer. Every puzzle is checked by solving it to exhaustion rather than stopping at the first solution found, so a second valid completion cannot exist. A puzzle with two answers tells a player who found the other one that they are wrong.
Never a guess. A puzzle that cannot be finished by a written-down list of human techniques is thrown away, not relabelled Expert. That matters more than it sounds: about a third of puzzles dug at random need reasoning past that list, and a generator that only checks for a single answer ships that third to players as the hardest tier.
Difficulty is which reasoning it demands, not how few numbers it starts with. The number of givens changes how long a puzzle takes, not how hard it is — grading by clue count is the most common flaw in free sudoku and produces wildly uneven difficulty.
How to play
- Choose a squareTap it
- Write a numberTap it on the pad
- Take it backTap the same number again
- Empty the squareClear this square
There is no pen-or-pencil switch. What is in the square already says what it is: one number is an answer and is drawn large, two or more are notes and are drawn small. A single pencil mark and an answer are the same thing logically, so nothing is lost by refusing to distinguish them — and the mode that every other touch sudoku loses track of simply does not exist.
Selecting a square tints its row, column and box, lights the numbers already in it on the pad, and tints every other square holding the same number. That last one is the most useful assist in sudoku and it costs nothing.
The honest cost: correcting an answer takes two taps rather than one, because you take the old number out and put the new one in. The pad showing what is in the square is what makes that second tap visible rather than remembered.
On a desktop, click instead of tapping, or just type: 1 to 9 write a number, Backspace, Delete or 0 empties the square, and the arrow keys move between squares. In a window wider than it is tall, the pad sits beside the grid instead of under it.
Nothing is punished
There is no error state while you play. Put a wrong number anywhere and the game says nothing. When the grid is full the status line tells you it is not right yet, and only if you ask are the wrong squares marked.
What isn't settled yet
Whether two taps to correct an answer is a cost people notice. The game counts corrections while you play so that this gets measured rather than argued about, but nobody has sat down in front of it yet.
Whether the note digits hold up at arm's length on a wall screen. They are small by necessity and have only been read at phone distance.
Build Log
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Build 3
Every puzzle ships only after two separate checks: that it has exactly one answer, and that a person can reach that answer using a written list of solving techniques. All 700 pass both. The second check is the one that earns its keep — a grid can have a single valid answer and still need reasoning no ordinary solver would find, and checking only the first would let those through labelled Expert. They are thrown out instead, which is why difficulty here is the hardest technique a puzzle needs rather than how few numbers it starts with. Worth writing down: “has one answer” and “can be solved” are different questions, and only the first is easy to test.
Credits and licences
No third-party engine and no embedded typefaces — it uses whichever fonts your device already has. Cover art was rendered from the game’s own grid-drawing code.
Nine Apart is original work by Launchway Games.