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Sudoku.

Logic puzzle · a fresh board every game, one solution each

Tap a square, then a number · ✎ switches to pencil notes · Keyboard: arrows to move, 1–9 to fill, N for notes, Backspace to erase

Level: —
Time: 0:00
Empty: —
Wrong: 0

The prompt

Make Sudoku in one HTML file. Generate a fresh full grid with randomised backtracking, then remove numbers one at a time, keeping each removal only if the puzzle still has exactly one solution. Easy, Medium and Hard by clue count. Highlight the row, column, box and matching numbers, flag clashes in red, support pencil notes, keep a timer, and save progress on the device.

Claude wrote this game from a short brief like this one. It was then played, tested on phones and tuned before it went up here.

How to play

Fill every row, column and 3×3 box with the numbers 1 to 9, each exactly once.
Numbers in bold were given and can't change.
Use pencil notes (✎) to jot down possibilities in a square.
Clashing numbers turn red. Your game is saved if you leave.