Anti-Knight Sudoku: rules, strategy and how to start
No two cells a knight’s move apart may hold the same digit. There is nothing to see on the grid — the constraint lives entirely in the geometry.
Why the rule changes everything
Every cell has up to eight knight neighbours, and they are spread across four different boxes. Placing a digit removes it from cells you were not looking at, which is why anti-knight puzzles feel harder than their clue count suggests.
The corner cells are the exception: they have only two knight neighbours, so corners are the loosest cells on the board and a good place to place early.
How to start a board
- Draw the knight graph in your head for one cell you care about — usually a corner or an edge cell with few neighbours.
- Use ordinary sudoku to get one digit placed, then immediately strike it from its knight neighbours.
- Work outward from corners; the centre of the board is where the knight net is densest.
Common mistakes
- Forgetting the second orientation of the move (one across, two down as well as two across, one down).
- Assuming boxes protect you — knight moves cross boxes precisely.
- Only checking the newly placed digit; a wrong elimination earlier propagates.
Frequently asked questions
What is anti-king then?
The same idea with a king’s move: the eight surrounding cells cannot repeat the digit. It is far more restrictive.
Does the rule replace sudoku?
No, it sits on top. Rows, columns and boxes still hold 1–9 once.
Every board on this site is generated with a uniqueness check, so the puzzle in front of you has exactly one solution and every digit can be proved rather than guessed.
Play Anti-Knight Sudoku ↗