Insane Sudoku

Welcome to Insane Sudoku, the hardest puzzles we offer. Each one needs forcing chains or forcing nets, following where a candidate leads until it contradicts itself, and rates 9.0 or higher on the Sudoku Explainer scale, a widely used measure of difficulty.

Techniques You'll Need

• Forcing Chains

  Following logical consequences of a candidate placement to identify contradictions or forced placements

• Forcing Nets

  Forcing chains that branch, following every consequence of a placement at once until one path contradicts another

• Almost Locked Sets

  Groups of cells where the number of candidates is one more than the number of cells, creating powerful elimination opportunities

• Alternating Inference Chains

  Complex chains that alternate between different candidates and different types of links to create powerful eliminations