Hard Sudoku: For Experienced Players

How to play

1. The game starts directly with a random hard sudoku. Use the menu to reach the daily puzzle or the easy and medium levels.
2. Fill the 9x9 grid so the digits 1 to 9 appear exactly once in every row, column, and 3x3 block.
3. Turn on notes mode and write down every remaining candidate in the empty cells.
4. Eliminate candidates as soon as a number is placed in the row, column, or block.
5. Mistakes and hints each cost 30 seconds. The grid is solved when all 81 cells are correct.

Tips and tricks

• Hidden single: if a number can only go in one cell of a block, it belongs there, even if that cell still has other candidates listed.
• Naked pair: if two cells in a row, column, or block share exactly the same two candidates, you can remove those numbers from every other cell in that unit.
• Aligned candidates: if a number in a block can only go in one row, it can no longer go in that row outside the block.
• Don't guess. A hard sudoku can feel stuck after a while; a second pass through every candidate beats a random attempt.

About Hard Sudoku

A hard sudoku has fewer starting numbers than an easy one, usually 22 to 26 instead of 35 or more, and those numbers are placed so that no cell is obvious. Anyone who only hunts for isolated missing numbers gets stuck fast. You need notes, hidden singles, naked pairs, and candidate elimination that reaches beyond block boundaries.

Every hard sudoku here has a guaranteed unique solution and can be solved without guessing. Mistakes and hints cost 30 seconds each, and your time counts toward the leaderboard. If you'd rather have the daily puzzle at hard level, you'll find it in the menu, alongside the easy and medium levels.