An example Anti-King puzzle: no cell a king's move from the 5 (the shaded ring) may also be a 5.
Anti-King Sudoku adds a chess rule to the ordinary grid: no two cells a king's move apart may hold the same digit. A king steps one square in any direction - including diagonally - so every cell now "attacks" the eight cells immediately around it, and none of them may repeat its value. It is a close relative of Anti-Knight Sudoku and a building block of the famous Miracle Sudoku.
The rule: a king's move can't repeat
Place a digit and it is locked out of all eight surrounding cells. In the diagram, the amber X forbids an X in every red cell - its full ring of neighbours. The ordinary rules still apply too, so the digit also clears its row, column and box; the king constraint stacks on top.
The centre X forbids that digit in all eight surrounding cells - the king's move.
The diagonals are what's new
Four of a king's eight neighbours - up, down, left and right - are already partly constrained by the ordinary rules, but the four diagonal neighbours are not: two diagonally adjacent cells often sit in different rows, columns and boxes, so plain Sudoku lets them repeat. The anti-king rule closes that gap. Its most quoted consequence is that no 2×2 block anywhere on the grid can contain the same digit twice - a handy check while solving.
Combined with the ordinary rules
Think of every placed digit as clearing not just its line and box, but a tidy 3×3 halo around itself. When you are working out where a digit can go in a box, remember to knock it out of the eight cells touching any existing copy nearby. That extra diagonal reach is what lets Anti-King grids be solved from fewer givens than Classic, and it combines with the anti-knight and non-consecutive rules to power the two-clue Miracle Sudoku.
Solving strategy
- Sweep the halo on every placement. After writing a digit, cross it out of all eight surrounding cells.
- Watch the diagonals. The diagonal bans are the ones ordinary Sudoku misses - they do the real work.
- Use the 2×2 rule. No 2×2 block may repeat a digit; scan for near-repeats as a quick check.
- Feed the grid. Each forbidden cell tightens a box, often leaving a digit a single home.
Common mistakes
- Confusing it with the knight. The king reaches the eight adjacent cells; the knight leaps in an L to farther cells. Anti-King uses the adjacent eight.
- Only checking orthogonally. The diagonal neighbours are the whole point - do not skip them.
- Treating it as a placement rule. It only forbids a repeat; it never forces a digit on its own.
- Dropping the ordinary rules. Rows, columns and boxes still need 1-9; the king constraint is an addition.
Can I play it here?
Not yet - Anti-King Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile:
- Browse all the Sudoku variants we do offer.
- Or print free puzzles from the printable PDF page.
Where to play it
Anti-King Sudoku belongs to the constraint family and runs on 9×9. It is not one SudokuStreak generates yet - but the deduction it trains is the deduction every Sudoku runs on.
Difficulty and type are two separate dials here: the type sets the extra rule, the level sets how much of the grid you start with. Expert Sudoku leaves 25 of the 81 cells filled, where the beginner tools dry up almost entirely; Evil Sudoku leaves 23, with no easy moves at all. Take it at the gentler end while the pattern is still new, and move up once it stops being a fight.