Complete a row
Which number completes this row?
12345678?
9 completes the row because all the other numbers from 1 to 8 are already present.
Sudoku Online
Play free easy, medium and hard Sudoku with clear hints, pencil notes and saved progress.
Difficulty
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Sudoku rules: rows, columns and boxes
A classic Sudoku has 81 cells arranged in a 9×9 grid, divided into nine 3×3 boxes. Fill the empty cells so that every row, column and box contains all the numbers from 1 to 9 exactly once.
The starting numbers are fixed clues. You can change your own entries, but not the clues. Sudoku uses logical placement, not arithmetic: you do not need to add, subtract or calculate a total.
123456789
This row already contains 1 through 8, so its final cell must be 9. In a full puzzle, check the cell’s column and box as well.
ⓘ A number with no immediate duplicate is not necessarily correct. It still needs to fit the rest of the puzzle.
Easy, medium and hard Sudoku
All three levels use a standard 9×9 grid. Difficulty is based on the deductions a puzzle requires, not a different board size.
Easy Sudoku for beginners
Start with clear, approachable deductions. Look for a row, column or box with only one number missing, or a cell with just one possible value. Easy is a good place to learn the controls and build confidence one move at a time.
Medium Sudoku with more to uncover
Use pencil notes to compare possibilities across different parts of the grid. A useful exclusion in one box may open a move in another row or column. Medium is for players who know the rules and enjoy connecting a few logical steps.
Hard Sudoku for a deeper challenge
Keep track of candidates and look for patterns that rule out several possibilities at once. Hard puzzles call for more involved reasoning, not faster tapping. Take your time and open a hint when you want help understanding the next step.
Change difficulty in the game controls above. Switching levels does not discard the unfinished puzzle in another level.
Use pencil notes and step-by-step hints
Notes: keep possibilities separate from answers
Turn on Notes, select an empty cell and choose the numbers that could fit. Small pencil marks record possibilities; they do not count as filled answers. Choose a marked number again to remove that note. Turn Notes off before entering a final answer.
Hints: a direction before the answer
Hint first points you toward an area worth examining. Choose Show why to see the reasoning, then Apply this step only when you want the move made for you. You can close the hint at any point and finish the deduction yourself.
Conflict warnings and answer checks are different
A conflict warning points out a repeated number in a row, column or box. Check puzzle goes further and compares your filled answers with the solution. Checks do not grade your pencil notes. Use either tool when helpful; mistakes do not end the game.
Music and sound effects
Use the speaker button to turn music and sound effects on or off together. Sound is optional and does not change the rules or your results.
Automatic note cleanup removes a number from related notes when you enter it as an answer. Undo restores the entry and the notes changed by that move.
Sudoku tips and strategies to get unstuck
You do not need to solve the whole board at once. Find one move you can explain, place it, then check what changed.
Start with the most complete areas
Scan rows, columns and boxes with few empty cells. Write down what is missing, then check where those numbers can legally go. A nearly complete area gives you fewer possibilities to compare.
Look for one possible value
For an empty cell, rule out the numbers already present in its row, column and box. If only one of the numbers 1–9 remains, it must go there. Do not treat a single handwritten note as proof unless you have checked all the other possibilities.
Look for one possible position
Choose a number missing from a row, column or box. If only one empty cell in that area can contain it, you have found its position—even if that cell still has other candidates.
Follow the effect of your last move
After entering a number, revisit its row, column and box. The new value may remove a candidate or leave another area with one missing number. If nothing is certain, keep notes and move to a different area instead of guessing.
Try one step
These short examples are separate from your puzzle. Practicing here will not change your game or its hint count.
Find the only candidate
Check the highlighted cell’s row, column and box. Which number can go there?
5 is the only candidate. Every other number from 1 to 9 already appears in the highlighted cell’s row, column or box.
Find the only position
In the highlighted row, where can 5 go? Select the only possible cell.
Only the selected cell in this row can contain 5. Every other empty cell is ruled out by a 5 in its column or box.
Frequently asked questions
Is this Sudoku free to play?
Yes. Play all three difficulties and use notes, undo and hints without creating an account or installing an app.
Which Sudoku level should I choose?
Choose Easy if you are learning the rules or want a gentler puzzle. Try Medium for more candidate-based reasoning, or Hard for a more involved challenge. All levels use a 9×9 grid.
Do I need to guess?
Aim for deductions you can explain rather than trial and error. Check another row, column or box, or use Hint for a logical next step. If earlier answers need checking, the game asks before comparing them with the solution.
Is there a time limit or a mistake limit?
No. The timer records your playing time; it is not a countdown. There are no lives to lose, and mistakes do not end your puzzle.
Can I save a puzzle and continue later?
Progress is saved automatically in this browser when storage is available. Return on the same device and browser to continue. Clearing site data, private browsing or blocked storage can remove or prevent saves. There is no account-based device sync.
Why can a number be wrong without a conflict warning?
A conflict warning checks for repeated numbers in the current grid. A wrong answer may not repeat anything yet. Check puzzle compares filled answers with the solution and does not evaluate pencil notes.
How do Sudoku hints work?
A hint offers a place to look, an explanation and an optional step to apply. Asking for help does not end the game or remove series progress. Your result records hints and answer checks so you can see how you played.
Why did some of my notes disappear?
Automatic note cleanup removes a number from related notes when you enter it as an answer. Undo restores the entry and the notes changed by that move.
Can I play on a phone or use a keyboard?
Yes. Use the on-screen number pad on a phone or tablet. On a computer, select the grid and use 1–9 to enter numbers, arrow keys to move and Delete or Backspace to erase. Press N to switch Notes on or off.
Where can I see my records?
The records card shows how many different puzzles you have solved and your best time at each difficulty. Records stay in this browser and include completions with hints or checks.
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