Anti-Knight Sudoku

Anti-Knight. Cells a knight's move apart cannot share the same digit.

How to play

Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1 to 9 with no repeats — the classic Sudoku rule. Anti-Knight Sudoku adds one twist: Cells a knight's move apart cannot share the same digit.

Anti-knight sudoku keeps every rule of the classic 9×9 grid and borrows one from chess: no two cells a knight's move apart — an L-shape of two squares one way and one square the other — may hold the same digit. From a central cell that L-shape reaches up to eight different targets, so placing a digit bans it from a scatter of cells that share no row or column with the placement. That extra web of constraints is what lets anti-knight sudoku resolve squares where ordinary row, column and box scanning would leave you stuck.

How to solve Anti-Knight Sudoku

After every digit you place, run through the eight knight offsets — two up and one across, one up and two across, and their mirrors — and delete that digit from each cell they land on. How many cells that touches depends on where you sit: a corner cell reaches only two knight targets, an edge cell three or four, but a cell in the central box reaches all eight, which is why placements near the middle do the most work and are worth chasing first. Every knight's move changes both the row and the column, so each elimination lands in a cell sharing neither line with your placement — genuinely new information ordinary scanning never produces — and most of those targets fall in a neighbouring box, giving you cross-box eliminations a classic grid simply cannot draw. Ignore the knight pairs that stay inside one 3×3 box, since the box's own no-repeat rule already covers them; the payoff is always the targets that leave the box, sometimes knocking a candidate out of three or four boxes at once. Fold these strikes into your usual hidden-single hunt — a knight elimination two boxes away is often the last cut that forces a digit into a single square — and remember that the commonest anti-knight slip is simply forgetting to sweep all eight L-shapes after a placement.

Every Anti-Knight Sudoku puzzle is free to play in your browser — no ads, no sign-up, and it works offline.

Frequently asked questions

What is Anti-Knight Sudoku?

Anti-Knight Sudoku is a 9×9 sudoku with one extra restriction taken from the chess knight: no two cells that are a knight's move apart may contain the same digit. A knight's move is the familiar L-shape — two cells in one direction and one at a right angle — so every filled cell forbids its digit in up to eight surrounding cells. All the standard rules still hold, so each row, column and 3×3 box must also contain 1 to 9 with no repeats.

What is a knight's move in Anti-Knight Sudoku?

It is exactly the move a knight makes in chess: from any cell, count two squares in a straight line and then one square at a right angle (or one square then two). That reaches up to eight cells — the same eight a knight could jump to — and none of them may share the digit you have just placed. Because both steps are non-zero, a knight's move always lands on a different row and a different column, and usually in a different box.

Does the anti-knight rule ever just repeat what normal sudoku already forbids?

Occasionally, and it is worth knowing which eliminations are the useful ones. A knight's move never keeps you in the same row or column, so those strikes are always new information. It can sometimes land inside the same 3×3 box — for example two cells one row and two columns apart in the same box — and there the ordinary box rule already bans a repeat, so the anti-knight constraint adds nothing. Every knight target that leaves the box, though, is a fresh elimination that classic sudoku has no way to make.