What Is Sudoku?
Sudoku is a number-placement puzzle built around a simple rule: each row, each column, and each 3×3 box must contain the digits 1 through 9 exactly once. The board has 81 squares. Some come filled with starting numbers, called givens, and you work out what belongs in the empty ones.
Despite the numbers, there is no arithmetic. A 9 is not bigger or more important than a 2; both are simply labels you must place without repetition. Every proper puzzle has a single completed arrangement consistent with its clues.
One reason people enjoy Sudoku online is how little setup it needs. Start during a short break, make a few moves, and return later. The challenge is still yours to solve.
How to Play Sudoku Online
If this is your first game, choose Easy and give yourself permission to ignore the timer. Accuracy and understanding matter more than speed.
1. Choose a difficulty
Easy starts you with more guidance from the given digits. Medium offers a balanced challenge, while Hard leaves more work for your own deductions. These are practical game levels rather than a promise that every puzzle will take a particular number of minutes.
2. Select an empty square
Click or tap a cell on the grid. Look at its row, column, and 3×3 box before entering anything. The fixed starting numbers cannot be changed. Related-cell highlighting helps you follow the three places that constrain your selected square.
3. Enter a number from 1 to 9
Use the on-screen number pad or your keyboard. The number you choose should not already appear in the same row, column, or 3×3 box.
4. Use Notes for uncertain cells
Switch on Notes when two or three digits still seem possible. Instead of committing to an answer, record the candidates you want to check later. Switch Notes off when the deduction is certain and place the final digit.
5. Check a difficult spot, then continue
The Check control can help you identify a problem. If you are stuck, Hint offers limited assistance without displaying an entire finished grid.
6. Finish the board or pause
When every cell is correctly filled, the game recognizes the completed puzzle. You can start another round at the same level or try a different one. If you leave early, the current puzzle can resume from its locally saved state when you return on the same browser and device.
Easy, Medium, or Hard: Which Sudoku Should You Play?
Start with Easy if you are learning the rules, have only a few minutes, or want a relaxed solve. These boards are good for practicing missing digits and obvious placements. Finding one correct move at a time builds a useful habit.
Medium is the everyday choice for many players. You may have to look beyond an almost-complete row and compare possible spots for the same digit in different boxes. Pencil notes become more helpful, but you can still make progress in manageable pieces.
Hard is for a longer, less guided session. It may ask you to track several candidates and recognize more involved patterns. The number of clues does not tell the entire story about difficulty. Choose the level that holds your attention.
Make the Most of Notes, Undo, and Hints
Notes are not the same as answers. Suppose a square could contain 3, 6, or 8. Recording those three candidates is a reminder of what is still possible, not a claim that one of them is correct. When another move removes 6 from that square's row, update the note and keep going.
A hint is best used as a nudge. Before asking, try to name the row, column, or box you have already checked. After the hint, look at why the placement works rather than clicking through the board. For longer explanations of logical techniques, the separate Sudoku Solver can walk through an existing 9×9 puzzle.
Errors appear only when you click Check, which compares your entries with the answer. Editing clears the marks; check again when ready. There is no mistake limit, so you can correct a cell and carry on.
Use Undo to reverse a digit, note, erasure, or hint placement. Redo restores an undone move until you make a different edit. If an immediate logical placement is unavailable, Hint asks before revealing one answer from the solution; that reveal is clearly labeled.
A Small Example: Find the Missing Number
Imagine the middle 3×3 box contains eight of the nine digits: 1, 2, 3, 4, 6, 7, 8, and 9. Only 5 is absent. If the remaining square in that box is blank and neither its row nor its column already has a 5, it must hold 5.
This is called a naked single because one cell has only one legal candidate. It may be an easy deduction, but the same principle helps unlock complex games. Every correct placement changes the available candidates in its row, column, and box. After you place that 5, another square elsewhere might suddenly become obvious.
Try scanning for one nearly complete group before hunting for elaborate patterns. On many Sudoku online boards, the first useful move is much simpler than you expect.
Practical Sudoku Strategies for a Steadier Solve
One technique is to focus on a single digit. Find all the 7s already on the board, then check which empty positions in neighboring boxes could still take a 7. A row or column containing a 7 rules out that digit in every other cell of that same row or column.
Another is to compare two empty cells within one box. If both can only take the same pair of digits, those digits cannot occupy other cells in that box. You do not yet know which of the pair goes where, but you have narrowed the puzzle without guessing.
Keep your candidate notes short enough to read. Filling every empty square with nine tiny numbers can make a simple puzzle feel overwhelming. If you find yourself making random choices just to move forward, stop and rescan the most constrained rows and boxes.
Play a Few Minutes or Stay for a Full Puzzle
This free Sudoku online game works for a quick coffee break or a longer quiet session. If you are on a phone, the number pad lets you play without a physical keyboard. On desktop, keyboard entry and arrow-key movement can be faster when you are concentrating on the grid.
Your progress is stored locally for convenience. That means the same device can remember the current board, but it is not an account-based cloud save. Changing browsers, clearing site data, or using a different device may mean starting a new game.
Prefer solving with a pencil? The Sudoku Generator makes printable 9×9 worksheets with answer keys. For a much bigger paper challenge, try the 16x16 Sudoku Generator.
Sudoku Online FAQ
Is this Sudoku online game free?
Yes. You can choose a difficulty and play a full classic 9×9 puzzle without registering or installing an app. The basic game, notes, hints, and progress controls are available in your browser.
Can I play Sudoku online on my phone?
Yes. Tap an empty cell and choose a digit from the number pad. The board is designed for touch as well as mouse and keyboard input. Turning the phone sideways can help if you prefer larger-looking cells.
Does Sudoku require math?
No. Although the board contains numbers, you do not calculate with them. The challenge is to work out which digit can occupy each position without repeating within a row, column, or 3×3 box.
What should I do if I make a mistake?
Use Undo or Erase to correct an entry, and Check if you are unsure where a problem lies. Starting clues remain fixed. A conflicting number does not mean the entire puzzle has become unsolvable; fixing the incorrect entry lets you continue.
Are notes the same as filling a cell?
No. Notes record possible digits in small form. A placed digit is your actual answer for that square. Use notes when you are uncertain and switch back to normal entry when only one candidate remains.
Will my Sudoku game be saved?
Your unfinished puzzle can be saved in the browser on the device you are using. This is convenient for returning after a break but is not cross-device synchronization or permanent cloud storage.
How can I get better at Sudoku?
Begin by finding missing digits in nearly complete groups. Next, practice naked singles, hidden singles, and simple candidate elimination. Explain to yourself why each move works; speed tends to follow familiarity. If you need more instruction, open a puzzle in the Sudoku Solver and ask for a single logical hint.
Ready for Another Sudoku?
Choose a level that suits your time, settle into the grid, and work through one clear deduction at a time. Your next puzzle is ready whenever you are.