Killer Sudoku

Einstein is the highest difficulty we offer, and every puzzle at this level carries a guarantee: solvable through pure logic, no trial and error needed. Our constraint propagation engine verifies each puzzle before it ships. If there's a solution, there's a logical path to it.

You'll need everything at once. Cage-sum elimination, hidden singles, the 45 rule, innies and outies, cage interaction chains, and occasionally X-Wing patterns adapted for cage constraints. The solving path is rarely linear. You might place three cells with basic techniques, stall, apply the 45 rule on row 7, get one new digit, then chain cage interactions across two boxes to break the middle section open.

These puzzles take time. A clean solve in under 30 minutes is genuinely fast. If you're spending an hour, that's normal. The satisfaction is proportional. For technique refreshers, the strategy guide covers everything you'll encounter at this level.