Hard Sudoku
A quiet grid. A proper challenge.
Nine digits. One solution.A little space to think.
Preparing your puzzle…
Take your time.
Your puzzle is right where you left it.
Choose a cell, then a digit. Use 1–9 and the arrow keys on a keyboard, or the number pad below. Pencil notes help you keep track of possibilities.
A hard puzzle. A clear place to think.
Fill the nine-by-nine grid with digits 1 to 9. Every row, every column, and every outlined three-by-three box must contain each digit exactly once. The starting clues stay fixed. Your goal is to fill every remaining cell correctly.
These are our own generated puzzles, checked for exactly one solution. Hard is our site’s rating: the puzzle needs more than singles and locked candidates, and can be completed with pair-based logic without guessing. Difficulty varies between Sudoku sites, and the number of starting clues alone does not decide our rating.
Small notes. Better deductions.
Select a cell, then choose a digit on the number pad. On a keyboard, use the arrow keys to move around the grid and the number keys to enter a value. Turn on Notes to record possible digits instead of committing a number.
Auto notes fills the candidates allowed by the numbers currently on your grid. When you enter a number, matching notes in its row, column, and box are removed automatically. You can still change your notes as your deductions develop. Incorrect entered numbers can affect the candidates, so check your assumptions if a part of the grid stops making sense.
Try to find a cell with only one possible digit, or a digit with only one possible home in a row, column, or box. When two cells in a unit are restricted to the same two digits, that pair can help remove candidates elsewhere. The next certain step is more useful than a quick guess.
Keep your place, and enjoy the progress.
Undo and Redo let you revisit up to 200 actions, including changes to pencil notes. Check highlights incorrect entries without ending the puzzle. A hint explains a useful step before you decide whether to fill the cell. Your timer measures active play, and Pause gives you a break.
Earn stars for meaningful progress and completed puzzles. Your current grid, notes, and earned achievements save in this browser when storage is available. You can continue playing if saving is blocked, but keep the tab open if you want to keep that current puzzle.
What makes these puzzles hard?
Our hard puzzles are checked by a logical solver. Singles and locked candidates alone do not finish them; pair-based deductions are needed, and the full supported logical method solves them without guessing. This is a rating for this site, rather than a claim that every other Sudoku site uses the same scale.
Can I change the starting clues?
No. The original clues identify the puzzle and remain fixed. Numbers you enter are shown in a different ink color. You can erase or change your own entries and notes.
Do wrong numbers end my game?
No. You can correct your entries and continue. Repeated digits in a row, column, or box are highlighted as conflicts. Check also finds entries that differ from the puzzle’s solution, including mistakes that do not yet create a duplicate. Recorded checks and detected mistakes stay in your attempt’s history when you undo.
Does asking for a hint affect achievements?
A requested hint counts as assistance, even if you choose to keep thinking rather than fill the suggested cell. You can still finish the puzzle and earn completion achievements. Any achievement that requires an unassisted solve checks the assistance used for the whole attempt.
Will my puzzle save if I leave?
Your current puzzle and pencil notes save in this browser when storage is available. A restored game waits for you to resume. Starting a new puzzle replaces the current grid after confirmation when a game is in progress. Saving in one browser does not transfer your progress to another device.
Can I restart the same puzzle?
Yes. Restart returns this puzzle to its starting clues. It keeps the attempt’s recorded assistance and mistake history, so restarting or undoing a completed puzzle cannot count the same victory again. Choose New puzzle for a fresh grid.
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