Hard Sudoku
Free hard Sudoku for experienced solvers. These puzzles genuinely require locked-candidate techniques — graded honestly, never just stripped of clues.
▶ Play Hard SudokuNo ads · no account · works offline
How to play Sudoku
Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1–9 exactly once. Tap a cell, then a number — or use Notes to pencil in candidates. There’s no guessing: every QZBrain puzzle is solvable by logic.
Frequently asked questions
What techniques do hard Sudoku need?
Hard puzzles require “locked candidates” (pointing/claiming) — spotting that a number in a box is confined to one row or column — on top of singles.
Is it free?
Yes — completely free, with no ads and no sign-up.
Do I need an account or an internet connection?
No account, ever. Once loaded it works fully offline; your progress stays on your device.
Enjoy the focus? QZBrain turns it into a calm daily habit — adaptive training for memory, attention, and speed. Free on web, iPhone, and Android. Or read more articles on brain training.