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How to Play Sudoku
If you have ever glanced at a Sudoku puzzle and felt intimidated by the wall of numbers, take a breath: Sudoku is far simpler than it looks. There is only one rule to learn, no math is involved, and once it clicks you will wonder why you ever found it puzzling. This guide walks you through everything a complete beginner needs to play your very first game with confidence.
What a Sudoku Grid Looks Like
A standard Sudoku puzzle is a large square divided into a 9×9 grid, giving you 81 small cells in total. Those 81 cells are also grouped into nine smaller 3×3 boxes, usually marked by slightly bolder borders. So you can think about the grid in three ways at once: as nine horizontal rows, as nine vertical columns, and as nine boxes. Keeping all three in mind is the heart of the game.
When you open a fresh puzzle, some cells already contain numbers. These starting numbers are called givens (or clues). You never change or erase a given. They are the anchors that make the puzzle solvable, and a well-made puzzle always has exactly one correct solution.
The One Rule of Sudoku
Here it is, the entire game in a single sentence: every row, every column, and every 3×3 box must contain the digits 1 through 9, each exactly once. That is the whole rule. No digit may repeat within the same row, the same column, or the same box.
Notice what this rule does not ask of you. The numbers are just symbols; you never add, subtract, or do arithmetic of any kind. You could swap them for nine different letters or nine colors and the puzzle would work identically. Sudoku is a game of pure logic, not mathematics. Just as importantly, a properly constructed puzzle never requires guessing. Every square can be worked out through reasoning alone. If you find yourself tempted to guess, that is a sign there is a logical step waiting to be spotted.
Your First Move: Scanning
The friendliest technique for a beginner is called scanning, and it flows straight out of the one rule. Pick a digit, say the number 5, and hunt for where it must go.
Start by looking across the whole grid for 5s that are already placed. Because a 5 cannot repeat in any row, column, or box, each existing 5 quietly forbids its entire row, column, and box from holding another. Now choose a single 3×3 box that does not yet have a 5. Cross off every cell in that box that shares a row or column with an existing 5 somewhere else on the grid. If you are left with only one empty cell where a 5 could possibly fit, congratulations: you have found a placement, and you can confidently write it in.
Repeat this for other digits and other boxes. Rows and columns that are already crowded with givens are the best places to start, because the more numbers surrounding an area, the fewer possibilities remain. Every number you place creates new constraints, which in turn reveal the next move. That cascading momentum is what makes Sudoku so satisfying.
Pencil Marks and Candidates
Soon you will reach cells where more than one digit still seems possible. Rather than hold all of that in your head, experienced players jot small notes in the corner of a cell listing every number that could legally go there. These notes are called pencil marks or candidates.
Candidates turn a fuzzy situation into a clear one. As you fill in other cells, you erase candidates that are no longer allowed, and eventually a cell will be left with just a single candidate, which becomes its answer. Playing on paper, this means a lot of tiny erasing; playing in a well-designed app like Samuraiku, candidate marks update instantly and cleanly, so you can focus on the logic instead of the pencil work. Once you are comfortable with candidates, you are ready to explore more advanced solving techniques that go beyond simple scanning.
How You Win
You win the moment every one of the 81 cells is filled and the one rule holds everywhere: each row, each column, and each box shows the digits 1 through 9 with no repeats. There is no timer forcing you and no score to chase unless you want one. A completed grid is its own reward, and there is a distinct little click of satisfaction when the final digit drops into place.
Common Beginner Mistakes
- Guessing instead of reasoning. If you place a number on a hunch, a single wrong guess can quietly corrupt the whole grid. Trust that a logical step exists.
- Forgetting the boxes. Beginners often check rows and columns but overlook the 3×3 box constraint. Always check all three.
- Not using pencil marks. Trying to track every possibility in your head leads to errors. Write candidates down.
- Ignoring a placed number. Each digit you enter changes what is possible nearby, so rescan the area after every move.
- Rushing. Sudoku rewards a calm, steady eye far more than speed.
Where to Go From Here
Once the basics feel natural, a whole world opens up. You can chase faster times, tackle tougher difficulty levels, or try inventive variants such as Samurai Sudoku, which overlaps five grids into one glorious challenge. The best way to improve is simply to play often, and an app that can generate infinite puzzles at every difficulty gives you an endless practice ground whenever you have a spare moment.
That is all there is to it. One rule, a little patient scanning, and a few pencil marks are everything you need to start solving today. Grab a puzzle, take your time, and enjoy the quiet, focused pleasure that has made Sudoku a beloved pastime around the world. Your first completed grid is closer than you think.