About Hard Sudoku
Hard Sudoku is where pencil notes stop being optional. With only 30 to 33 clues, you will regularly reach positions where no cell has a single obvious answer, and progress comes from eliminating candidates instead.
The good news: hard boards reward method more than talent. If you keep your notes tidy and look for pairs, the puzzle opens up one elimination at a time.
Every hard puzzle is checked by our step-by-step solver before you see it: it must need techniques up to pairs & triples — and at least locked candidates. So the label always matches the challenge. Stuck? The hint button names the technique and walks you through it.
Best for
Confident solvers ready to work with candidates and pairs.
Techniques you will use
- Naked pairs
- Hidden pairs
- Pointing & claiming
- Systematic candidate notes
How to approach hard Sudoku
- Fill in candidates for a whole box or row at once rather than one cell at a time, so you can see patterns across cells.
- Naked pair: two cells in a unit that share the same two candidates own those digits — remove them from every other cell in that unit.
- Pointing: if a digit's candidates inside a box lie on one line, that digit can be removed from the rest of the line outside the box.
- After every placement, update the notes of the affected row, column and box. vSudoku removes the placed digit from peer notes automatically to save you time.
Want the full method? Read our Sudoku tips and strategy guide or the beginner's guide to playing Sudoku.
Frequently asked questions
Why is hard Sudoku so much harder than medium?
Fewer givens mean fewer direct deductions. Instead of spotting where a number must go, you often have to work out where it cannot go — that is what notes and pairs are for.
Is guessing allowed?
You can, and undo makes it painless, but you never need to. Every hard puzzle here has exactly one solution reachable by logic.
What technique should I learn first for hard puzzles?
Naked pairs. They appear constantly at this level and unlock most of the positions where you feel stuck.