A strategy for medium puzzles
A hidden single is a number that has only one possible cell in a row, column or box, even if that cell has other candidates.
What makes these puzzles medium
Each medium puzzle needs at least one locked-candidate step. If all the cells for a number inside a box share one row, that number cannot appear anywhere else in that row. Removing it there often reveals the next single.
Keep notes tidy
After every placement, remove that number from the notes in the same row, column and box. Most stalls in medium puzzles come from an outdated note rather than a missing technique.
Use the tools at your own pace
Notes record possibilities. Undo reverses your last change, one move at a time. Fill notes lists candidates from your current entries; Redo restores an undone move. Restart replays the same starting puzzle. A hint explains a step before placing a number. Pause hides the grid and stops the timer, and your game is saved on this device so you can come back later.
Moving between levels
Feeling stuck often? Go back to easy Sudoku for a few rounds. Finishing comfortably? Hard Sudoku adds pairs and triples. Our Sudoku tips explain each technique with an example.
Ready for another puzzle?
Choose New puzzle to start again, or visit the daily challenge for a puzzle that stays the same throughout the day. Prefer paper? Make a printable Sudoku sheet at the same level.
A few helpful answers
Yes. The game works in your browser. Progress is saved on this device when local storage is available.
Turn Notes on, select an empty cell, then choose numbers to add or remove pencil marks. Turn Notes off to enter a final number.
Yes. Every puzzle has exactly one solution, and our step-by-step solver finished each one using logical techniques before it was published.
With Auto-check on, a number that does not fit the finished grid gets a red outline and is counted as a mistake. There is no game over. Turn Auto-check off in the settings if you prefer to find errors yourself.
Yes. Use the arrow keys to move, type 1 to 9 to enter a number, press Backspace or Delete to erase, N to switch Notes on or off and U to undo.