What makes a Sudoku hard?
Difficulty is assigned from the hardest logical technique and the number of verified solving steps, not from guesswork.
hard Sudoku
A verified puzzle at the right pace.
Hard Sudoku changes the depth of the logical path, not the rules. Every row, column, and box still uses 1 through 9 exactly once.
This puzzle has one verified solution. Notes, keyboard controls, local saving, and explainable hints are available without an account.
Common questions
Can I continue later?
Yes. Your current grid is stored locally on this device and restored when you return.