Enter a number
Keyboard Shortcuts
Arrow keys — navigate cells
1–9 — place digit
N — toggle notes mode
H — hint
Ctrl+Z — undo
Backspace / 0 — erase
How to Play Sudoku
Choose Your Difficulty
Click one of the four difficulty tabs at the top — Easy, Medium, Hard, or Expert — to start a new puzzle at that level. Easy puzzles provide the most clues (36–46 pre-filled cells) and are great for beginners. Expert puzzles leave just 17–21 cells filled in and require advanced logic to solve. A new puzzle is generated instantly in your browser.
Select a Cell and Enter a Digit
Click or tap any empty cell to select it. Its row, column, and 3×3 box will be highlighted so you can quickly see which digits are already used in those regions. Then click a number on the on-screen number pad (1–9) or press a digit key on your keyboard. If you are on desktop, use the arrow keys to move between cells. The cell turns red if your entry conflicts with the puzzle's solution.
Use Notes to Track Candidates
When you are unsure which digit belongs in a cell, click the Notes button (or press N) to enter pencil-mark mode. In this mode, clicking a digit places it as a small candidate note inside the cell rather than a confirmed answer. You can place multiple candidates in one cell. When you confirm a digit in that cell or an adjacent peer, the corresponding notes are automatically removed from all peer cells in the same row, column, and box.
Use Undo and Hints Freely
Made a mistake? Click Undo (or press Ctrl+Z) to step back through your moves one at a time — there is no penalty for undoing. If you are completely stuck, select a cell and click Hint (or press H) to reveal its correct value. Your time, mistake count, and hint count are all tracked and shown in the completion summary when you finish the puzzle. Click New Game at any time to start a fresh puzzle.
Frequently Asked Questions
How do I use pencil notes in Sudoku?
Pencil notes (also called candidates or pencil marks) are small digit annotations you place inside a cell to remind yourself which digits are still possible for that position. To use them, click the Notes button on the control panel — it will turn highlighted to show notes mode is active. Now clicking any digit on the number pad places that digit as a small mark inside the selected cell rather than a confirmed answer. You can add multiple candidates to one cell. When you eventually place a confirmed digit in a peer cell (same row, column, or box), this game automatically removes that digit from all peer cells' notes. Press N on the keyboard to toggle notes mode on and off quickly.
What does the cell highlighting mean?
When you click a cell, three types of highlighting appear simultaneously. First, the selected cell itself gets the strongest highlight in the primary accent color. Second, all cells in the same row, column, and 3×3 box as the selected cell are shown with a softer background — these are called 'peer cells' and they are regions that cannot contain the same digit as the selected cell. Third, if the selected cell contains a digit, every other cell on the board that already contains the same digit is highlighted in a third shade. This same-digit highlighting helps you quickly spot where a digit has already been placed across the entire board and where it still needs to go.
What happens if I make a mistake?
If you enter a digit that does not match the puzzle's unique solution, the cell text turns red to indicate an error, and the mistake counter in the top bar increments by one. Mistakes are tracked and displayed in the completion summary at the end of the game, but there is no game-over condition — you can have as many mistakes as you like and still complete the puzzle. To correct a mistake, click the cell and click the correct digit, or press Backspace/Delete to erase it. You can also use the Undo button to step back to the state before the incorrect entry was made.
Will my progress be saved if I close the browser?
Yes. This Sudoku game automatically saves your entire puzzle state to your browser's local storage every time you make a move. This includes the board, your notes, the timer, mistake count, and hint count. When you return to the page, your game resumes exactly where you left off. Note that local storage is tied to the specific browser and device you are using — your progress will not carry over to a different browser, a private/incognito window, or another device. Clearing your browser's local storage or site data will erase your saved progress.
What is the minimum number of clues needed for a valid Sudoku?
The mathematical minimum for a Sudoku puzzle that has a unique solution is 17 clues. This was proven rigorously in 2012 by Gary McGuire, Bastian Tugemann, and Gilles Civario after a comprehensive computer search. No valid Sudoku puzzle with only 16 given clues can have a unique solution. Our Expert difficulty level targets 17–21 clues, which means some Expert puzzles are right at this theoretical boundary. In practice, 17-clue puzzles are extremely difficult and even many experienced solvers need to use advanced techniques or systematic trial-and-error to crack them.
What are some basic Sudoku solving strategies?
The simplest strategy is the 'last free cell': if a row, column, or box has eight digits filled in, the ninth cell must contain the only missing digit. Next is 'single candidate': if a cell has only one digit that can possibly go there after eliminating all digits already present in its row, column, and box, place that digit. 'Hidden singles' means a digit can only go in one cell within a row, column, or box even if that cell appears to have multiple candidates. For harder puzzles, 'naked pairs' (two cells in a region that can only contain the same two digits), 'pointing pairs', and 'X-Wing' patterns become necessary. Most Easy and Medium puzzles on this site are solvable using only the first three strategies.