Controls at a glance
Keyboard
Arrow keys move the selection, 1 to 9 place a digit, Delete, Backspace or 0 erases. N toggles notes (or hold Shift with a digit), U undoes, H gives a hint. P pauses, R restarts.
Touch screen
Tap an empty cell, then tap a digit on the number pad. Long-press a pad digit to pencil it in as a note. Erase, Undo, Notes and Hint buttons sit by the grid.
How to play Sudoku
Sudoku is played on a nine-by-nine grid divided into nine three-by-three boxes. Some cells are already filled with digits; your job is to fill the rest so that every row, every column and every box contains the digits one through nine exactly once, with no repeats.
Click or tap any blank cell to select it, then enter a digit on your keyboard or tap the number pad beneath the grid. Correct digits turn green with a short chime, and wrong digits show in red with a wavy underline until you change them. The puzzle is solved when every cell holds the right digit.
Turn on Notes to pencil small candidate digits into a cell. Undo steps back through your moves, and you get 3 hints per puzzle: a hint fills the selected cell (or the easiest open cell) with the right digit.
There is always exactly one valid solution. You cannot guess your way through: every digit you place must be forced by the digits already on the board.
Easy, medium and hard
Each difficulty level changes how many digits are given at the start:
- Easy – about 41 given digits. Most cells can be solved by looking at a single row, column or box at a time.
- Medium – about 31 given digits. You will need to cross-reference two constraints before placing some digits.
- Hard – about 25 given digits. Many cells require holding several possibilities in mind at once; pencil marks help.
All puzzles are generated fresh from a seeded random number generator, so every daily challenge is identical for every player on the same date while free-play puzzles are always unique.
Solving tips and techniques
- Single candidate – if only one digit is possible in a cell (all others appear in its row, column or box), place it immediately.
- Single position – if a digit can appear in only one cell within a row, column or box, it must go there.
- Elimination by box – if a digit is confined to one row or column within a box, it cannot appear in that row or column in the other boxes.
- Pair and triple exclusion – when two cells in a unit share the same two candidates, those digits can be removed from all other cells in that unit.
Hard puzzles may require combining several of these steps. Work through the easiest cells first to unlock harder ones.
Daily challenge and streaks
Switch to Daily challenge to play a puzzle that is the same for everyone on that date. Finish it on consecutive days to build your streak. Your streak and your fastest times per difficulty are stored in this browser, so no account is needed.
After you finish, press Challenge a friend to copy a link that opens the exact same puzzle at the same difficulty, so you can compare times. The clock only runs while you play: it starts with your first move and stops while the game is paused.
Stars depend on your time. Easy earns 3 stars under 5 minutes and 2 under 10, medium 3 under 10 minutes and 2 under 20, and hard 3 under 15 minutes and 2 under 30. Any finish earns at least 1 star.
Frequently asked questions
Is the puzzle always solvable?
Yes. Every generated puzzle has a unique solution that can be reached by logic alone, without guessing.
What do the red digits mean?
A red, wavy-underlined digit does not match the solution. Erase it or undo and try again. The Mistakes counter adds one for every wrong digit you place.
Can I use pencil marks?
Yes. Press N or tap Notes to switch to notes mode, then enter digits as small candidates. You can also hold Shift with a digit key, or long-press a digit on the pad. Placing a digit clears that candidate from the cells it sees.
Are there hints and undo?
Yes. You get 3 hints per puzzle (H key or the Hint button), each filling one cell with the right digit, and Undo (U) steps back through your moves.
Is my progress saved?
Yes. Your unfinished board and its time are saved in this browser after every move, so a reload or a closed tab continues where you left off. Best times per difficulty and your streak are kept too. Clearing site data removes them.
How is the daily puzzle chosen?
Each difficulty has its own daily puzzle built from the date, so everyone who picks the same difficulty on the same day gets the same grid. A new one appears at midnight in your time zone.
