Originally featured on freegamenews.com (whose domain is now up for sale) at tophatpuzzle.com, the original Flash module had a critical flaw: it did not ensure unique solutions, forcing players to guess between ambiguous endings. When the developer, Domas, disappeared and Flash died, we tapped the puzzle database and added a strict constraint-satisfaction uniqueness verifier.

Every board in Tophat Sudoku is verified to have exactly 1 valid completion. Click "💡 Deductive Hint" at any time to see the exact logical naked-single or hidden-single deduction!