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Sudoku is a logic puzzle where the goal is to fill a 9×9 grid with the numbers from 1 to 9. You need no math skills. It's all about logic and a little patience. Four simple rules are all it takes. Click a rule, and the board shows you exactly what it means.
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Fill the grid
A sudoku board has 9×9 cells, and some numbers are filled in beforehand. These are your clues. The goal is to fill each empty cell with a number from 1 to 9, using only logic.
Each horizontal row must eventually contain all the numbers from 1 to 9. Each number must appear exactly once, neither more nor less.
In the same way, each vertical column must contain all the numbers from 1 to 9. Each number can only appear once.
The board is also divided into nine boxes of 3×3 cells. Each box must also contain the numbers from 1 to 9, once each. These three rules apply at the same time all the time.
Each row 1 to 9
The goal is to fill the row with all the numbers from 1 to 9. Each number must appear exactly once.
The number 9 is already in this row. Placing another 9 would create a duplicate and leave no room for all the other numbers, so it is not allowed.
Each column 1 to 9
The goal is to fill the column with all the numbers from 1 to 9. Each number must appear exactly once.
The number 7 is already in this column. Each number can appear only once, or there will not be room for all nine numbers. That is why 7 cannot go here.
Each box 1 to 9
The goal is to fill the box with all the numbers from 1 to 9. Each number must appear exactly once.
The number 9 is already in this box. Since each number can appear only once, another 9 would create a duplicate. That is why it is not allowed.
Strategy
How to improve your skills?
Three techniques take you from guessing to pure logic. Choose a technique and flip through the steps. The board shows what happens.
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Naked Single
A naked single is a cell that has only one possible number left. It's the simplest technique, and it's perfect to start with.
We look at the highlighted cell. To find the number that fits, we check the row, column and box it's in.
First we write in all the numbers from 1 to 9 as candidates. Then we can see which of them are actually possible.
The numbers 1, 2, 3, 4, 6, 7, 8 and 9 already exist in the row, column or box. Because a number can only appear once, we cross them out.
Then only 5 is left. Because all the other numbers are excluded, 5 must go here. This is what we call a naked single.
Hidden Single
A hidden single is a number that only fits in one cell in a box, row or column. This applies even if that cell could also take other numbers.
We look at this box and ask: where can the digit 8 go? Five cells are still empty.
The number 8 already appears in these rows and columns. Because 8 cannot be repeated, it can't go in the cells they cross, so we cross them out.
Then only one free cell is left for 8. Because 8 must go somewhere in the box, it must go right here. This is what we call a hidden single.
Candidate notes
When you note which numbers are possible in each cell, both naked and hidden singles become much easier to see.
When you're unsure what goes in a cell, you can write small numbers in the corner. These are called candidate notes.
We write in all the numbers that are still possible in each cell. Then we can quickly see which cells have only one number left, and which numbers only fit in one place.
These are just three of the techniques. There is a dedicated page with all the Sudoku techniques from easy to brutal, each with interactive examples.
Extreme and Brutal are made for players who master the most advanced techniques. The boards are very demanding, and we recommend that you play Hard first.
Extreme
These puzzles require advanced techniques and plenty of patience. They are the natural next step after Hard.
A daily Sudoku routine provides mental stimulation and a welcome break from everyday life. Many people make a puzzle part of their morning ritual or take a Sudoku break at work. Here are the benefits:
Strengthens the brain
Playing Sudoku stimulates the brain and trains both working memory and mental flexibility. It's brain training at its best!
Increases focus
Sudoku requires concentration. With daily training you'll notice that your focus lasts longer, even outside the game.
Improves problem-solving skills
Regular problem solving gives you better strategic understanding and makes it easier to think critically and in a structured way.
Questions and answers
What people wonder about
Wondering how today's challenge, difficulty levels or accounts work? We've gathered answers to the most common questions in one place.
Yes, Sudokuen is completely free. You can play as much as you want without payment, subscription or hidden costs. You don't even need to create an account to get started.
Yes! There is a new daily challenge every day, and you can also start unlimited easy, medium and hard puzzles whenever you like. You will never run out of new Sudoku puzzles.
Ads will never interrupt your game. The puzzle itself is always clean and free of pop-ups, so you can solve Sudoku in peace. It is just you and the puzzle.
Yes, you play Sudokuen directly in your browser. There is no app to download or software to install, and it works on mobile phones, tablets and computers.
Yes, you can choose between easy, medium and hard, with levels for beginners and experienced players alike. Today's challenge also gives you a new puzzle to test yourself on every day.
Yes, Sudokuen is available in English. You can also switch to Norwegian or another language if you prefer.
No, you can play completely freely as a guest without registering. If you create a free account, you can also save your progress, collect points and track your statistics over time.