About game
Logic puzzles push your brain to the limit when standard grids become too predictable. Hard Sudoku transforms simple number placement into a rigorous mental workout that scales from casual practice to near-impossible challenges. Nine distinct difficulty settings ensure you always find a task that tests your current cognitive capacity. You place digits into the nine by nine grid while navigating strict rules about rows, columns, and blocks. Every puzzle has exactly one logical solution, so you never have to worry about ambiguous results. Advanced hint mechanics provide detailed explanations of specific techniques rather than just revealing the answer. Cloud synchronization keeps your progress and stats secure across your devices whenever you sign in. You can try Hard Sudoku for free in your browser right now without downloading a single file.
How to play
Fill the 9×9 grid so that the digits 1 to 9 never repeat in a row, a column or a 3×3 block. The given digits are open from the start and cannot be changed.
— The input scheme and the interface language are chosen in Settings. Digit first: a digit stays held down on the keypad and taps on the grid place it. Cell first: a tap selects a cell and digits go into it. Automatic: the game follows your first action.
— Entering the same digit again erases it. The eraser works as a mode: every tap clears a cell.
— Notes turn the keypad into a pencil — candidates go into the cell. A digit you write erases the same notes in its row, column and block.
— Undo and Redo roll moves back and forward.
— Three buttons run on a watched ad: Hint finds the next move and explains it (up to three per puzzle), Check the grid compares your grid with the solution, Auto notes fill candidates across the whole board.
— On a computer the digit keys, arrows and Backspace work too.
Features
- Difficulty scaling: Choose from nine tiers ranging from Very Easy to the brutal Legend level.
- Instructional hints: Each hint explains the underlying logic and technique behind a move to help you improve your skills.
- Error detection: Highlight conflicts instantly if you place the same digit twice in a row, column, or block.
- Persistent progress: Store multiple unfinished games and track your performance statistics through the integrated cloud system.
- Input flexibility: Switch between digit-first, cell-first, or automatic input modes to match your personal playstyle.
Who is it for
Logic enthusiasts craving a brain challenge and puzzle veterans wanting to sharpen their analytical skills will find plenty to love here. Anyone who enjoys the satisfaction of solving complex, number-based grids will appreciate the deep progression and statistics found within this rigorous digital version of the classic game.
Controls
Select cell
Tap the desired grid square on your screen or click it with your mouse.
Input digit
Tap or click the number from the keypad after selecting a cell.
Toggle notes
Activate pencil mode to place candidate digits inside a cell using tap or click.
Erase number
Tap the eraser icon or tap the same digit again to remove it from the grid.
FAQ
How do I win at Hard Sudoku?
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You win Hard Sudoku by filling every cell in the grid with numbers one through nine so that no digit repeats in any row, column, or three by three block.
Can I play Hard Sudoku on my phone?
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Yes, Hard Sudoku runs directly in your mobile browser, allowing you to tap and swipe your way through puzzles anywhere.
Are there too many guesses required in Hard Sudoku?
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Every puzzle in Hard Sudoku has one unique solution, meaning you can solve everything using pure logic without ever needing to guess.
