Play Knight Killer Sudoku Online Free

Play Knight Killer Sudoku online for free. Killer cages combined with the anti-knight constraint — cells a chess knight's move apart cannot contain the same digit.

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How to Play Knight Killer Sudoku

  1. Standard Sudoku rules: every row, column, and 3×3 box contains 1-9.
  2. Dotted cages show a target sum — digits inside must add up to it, with no repeats inside a cage.
  3. Cells a chess knight's move apart (1+2 or 2+1 squares) cannot contain the same digit.
  4. Each placed digit eliminates itself from up to 8 knight peers, dramatically tightening candidate sets.
💡 Pro Tip
Place the digit 5 in the centre 3×3 box first — its knight peers reach all four neighbouring boxes and propagate eliminations fast. Pair knight sweeps with cage Rule of 45 for the strongest deductions. When a cage spans two boxes, the knight rule often rules out pair combinations that would satisfy the cage total — combine cage arithmetic with peer elimination on every step.

Frequently Asked Questions

What is the anti-knight constraint?

Two cells whose row and column differ by (1,2) or (2,1) — like a chess knight's move — cannot share the same digit. Most central cells have 8 knight peers.

Is Knight Killer harder than regular Killer Sudoku?

Often easier per clue because the knight rule eliminates many candidates instantly, but the deductions are different — you alternate cage arithmetic with knight-peer sweeps.

How is Knight Killer different from King Killer?

Anti-knight reaches further across the grid (up to 8 peers per cell, in different boxes) while anti-king is denser locally (4 diagonal peers). Knight constraints often produce hidden singles in distant boxes; king constraints tighten 2×2 blocks.

Which cells have the most knight peers?

Centre cells have all 8 knight peers; corner cells like R1C1 have only 2. Place corner cells last and centre cells first to maximise constraint propagation.

Try More Puzzle Modes

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