Sudoku · Hard
Hard puzzles for advanced solvers: locked candidates and subsets required — but pure logic always wins, no guessing.
Hard · #1
Settings
Tap a cell, then a number.
Sudoku FAQ
How do you solve hard sudoku puzzles without guessing?
With candidates and eliminations. Keep full pencil marks, then use locked candidates and pairs to strip impossible digits until new singles appear. Every hard puzzle here is machine-verified to fall to exactly this kind of reasoning — guessing is never required.
What techniques do hard sudoku puzzles require?
Beyond singles: locked candidates, plus naked and hidden pairs — two cells in a unit that lock up the same two digits, letting you erase those digits elsewhere. The Hint button can show the next such step whenever you want a nudge instead of an answer.
Is it OK to guess in hard sudoku?
You never need to here, and it rarely pays: one wrong branch can quietly poison the whole grid. When stuck, first check your candidates for mistakes, then rescan for singles — the logical path is always open.