Anti King Sudoku (PuzzleMadness)

The normal sudoku rules apply, with 1 to 9 once in every row, column and 3x3 box. The extra rule borrows the chess king, which moves one square in any direction. In Anti King Sudoku, two cells a king's move apart may not hold the same digit, so a 7 rules out 7 from all eight cells surrounding it.

Inside a box this changes nothing, because a box never repeats a digit anyway, and the same goes for cells directly above, below or beside each other. What is new is the diagonal step across a box border: the corner of one box touches the corners of its neighbours, and those diagonal pairs must now differ. With no marks on the grid to remind you, the rule is easy to overlook, and it is often the step that breaks a stuck position.

The grid works like every sudoku on PuzzleMadness: number buttons above and below it, an eraser, and a pencil mode for candidate digits. On a keyboard, the number keys enter digits, the arrow keys move between cells, Ctrl, Shift or Alt with a number adds a pencil mark, and Delete or Backspace clears a cell.

PuzzleMadness is a free puzzle website run by Dewi, a software developer who started out making games for the PlayStation 2, Nintendo Wii and DS and now builds the site as a hobby. It carries dozens of puzzle types, from classic sudoku to newer logic grids, and each one gets its own dated puzzle every day at each difficulty. Anti King Sudoku comes in Easy, Medium, Hard and Tough versions. The Mixed page has a fifth grid of its own whose level changes from day to day, and on 28 October 2026 it was an Easy one. Every grid is shared by everyone who opens it that day.

The site checks your grid as you go and tells you when it is finished; it does not publish solutions. Each completed puzzle earns a score, and scores feed a monthly and an all-time Anti King Sudoku leaderboard, where only your best attempt at a puzzle counts. Older days stay in the archive, so a missed puzzle can still be played later and still counts toward the current month. Playing needs no account; a free registration gives you a username on the leaderboards and a cloud save. The pages carry adverts.