Free online anti-knight sudoku — expert difficulty
Anti-Knight Sudoku follows all standard Sudoku rules, plus one extra constraint: no two identical digits can be a chess knight's move apart (an L-shape: 2 squares in one direction + 1 square perpendicular).
In the diagram above, if the center cell contains a 5, then none of the red cells can also contain a 5.
Expert Anti-Knight Sudoku is our hardest difficulty level, designed for experienced puzzle solvers who want to push their logical reasoning to the absolute limit. With only around 24 given digits to start, every move counts, and the knight constraint is not just an extra rule — it's often the only way forward.
An expert Anti-Knight Sudoku puzzle typically takes 30-60 minutes to solve, even for experienced players. You'll encounter positions where multiple advanced techniques must be chained together. The knight constraint frequently provides the critical breakthrough when all other techniques appear to fail. Every puzzle has exactly one solution reachable through pure logic — no guessing required.
At expert level, you'll rely on techniques like Swordfish, XY-chains, coloring, and forcing chains. Anti-Knight Sudoku adds a unique twist: any of these techniques can incorporate knight-move relationships. Look for knight-pairs (two cells a knight's move apart that must share a candidate set), and use them to force eliminations elsewhere on the board.
Expert Anti-Knight Sudoku is not for the faint of heart. If you haven't mastered hard Anti-Knight Sudoku yet, we strongly recommend practicing there first. When you're ready, dive in — and remember, there's no shame in using hints or taking breaks. Some expert puzzles are best tackled over multiple sessions. Check out our comprehensive rules guide for advanced strategies.