Hard puzzle
Hard Sudoku
Play hard Sudoku online for free with notes, hints, and careful candidate-based solving practice.
DifficultyHard
Mistakes0/3
Time00:00
Practice guide
How this hard puzzle works
Hard Sudoku is for players who enjoy slower, more deliberate solving. Progress often comes from candidate cleanup, hidden singles, locked candidates, and comparing several regions at once.
Candidate disciplineLonger solve timesAdvanced scanning
Solving tips
- Keep notes consistent across every row, column, and box.
- Search for hidden singles inside a 3x3 box before trying advanced patterns.
- When stuck, review every recent placement and remove candidates it affects.
Frequently asked questions
Why do hard Sudoku puzzles feel stuck?
Hard puzzles often hide the next move in candidate notes rather than in the visible givens. Cleaning up notes usually reveals the path.
What technique should I learn after singles?
Locked candidates are a strong next step. They let you eliminate candidates when a digit is confined to one row or column within a box.