# How to Play Sudoku: The Rules and the Techniques That Work Canonical page: https://rovixel.com/sudoku/how-to-play/ Learn how to play sudoku from scratch — the three rules, how to scan the grid, and the beginner techniques that solve most puzzles without guessing. Part of [Sudoku](https://rovixel.com/sudoku.md). Sudoku looks like a maths puzzle and is not one. There is no arithmetic anywhere in it — you never add, subtract or multiply. It is a logic puzzle about placement, and once the three rules are clear, the rest is pattern recognition you can learn in an afternoon. ## The rules A sudoku grid is nine squares wide and nine squares tall, split by heavier lines into nine 3×3 boxes. Some squares already contain a number from 1 to 9; the rest are empty. To solve the puzzle you fill every empty square so that three conditions hold: 1. **Every row** contains each of the numbers 1 to 9 exactly once. 2. **Every column** contains each of the numbers 1 to 9 exactly once. 3. **Every 3×3 box** contains each of the numbers 1 to 9 exactly once. That is the whole game. There is no other rule, and a well-made puzzle has exactly one solution. ## How a game goes You start with the given numbers and work out what the empty squares must be. The key move is always the same: look at a row, a column or a box and ask which numbers are still missing, then find the one empty square where a missing number can legally go. The very first technique is called **scanning**. Pick a number — say 4 — and look at where the 4s already are. Because every row, column and box needs a 4, the existing 4s rule out most of the grid. Often only one square in a box can still take a 4, and you have your next placement. Then you scan for the next number, and repeat. ## The techniques, from easiest to hardest **Naked single.** A square where eight of the nine numbers are already ruled out by its row, column and box. Only one candidate is left, so it must be that number. Beginners find these by scanning; experienced players find them without thinking. **Hidden single.** A square that does not look forced on its own, but is the only square in its row, column or box where a particular number can go. If a 7 can only fit in one place within a box, that square is a 7 even if it has other candidates. **Naked pair.** Two squares in the same row, column or box that can only contain the same two numbers. Those two numbers must occupy those two squares, so you can remove them from every other square in the unit. This is the first technique that solves puzzles the simple scans cannot. **Pointing.** When a candidate in a box can only appear in one row or column, it "points" along that line and can be removed from the rest of the line outside the box. It is the mirror image of a hidden single. Everything beyond this — X-wings, swordfish and the rest — is a refinement of the same idea: find a constraint, then use it to remove candidates until only one is left. ## Sudoku for beginners If you have never finished a puzzle, start with an easy grid and give yourself permission to be slow. Easy sudoku is solvable entirely with scanning and naked singles, which means you never have to guess and you never have to hold more than one idea in your head at once. Two habits make the first puzzles much easier: - **Use pencil marks.** Write the possible candidates in each empty square instead of trying to remember them. The moment a grid is too big to hold in your head, notes are what keep you from losing your place. - **Never guess.** A guess that happens to be right teaches you nothing and a guess that is wrong can leave you with a broken grid. If you are stuck, you have missed a constraint, not run out of logic. Difficulty in sudoku comes from how many candidates you have to track, not from any hidden maths. A hard puzzle is one where the next placement needs a pair or a pointing deduction rather than a plain scan. ## Tips that make you faster 1. **Scan number by number, not square by square.** Pick a digit and sweep the whole grid for it. It is much faster than staring at individual squares. 2. **Finish the easy placements first.** Every number you place removes candidates elsewhere, so the grid gets easier as you go. 3. **Do the boxes in order.** Move through the nine boxes systematically so you do not scan the same one twice and skip another. 4. **When stuck, switch units.** If a row is not working, look at the boxes that cross it. The constraint you missed is usually in the other direction. 5. **Stop while you are ahead.** Fatigue is what turns a solvable grid into a guess. Come back to it fresh. ## Play sudoku in your browser [Sudoku](https://rovixel.com/sudoku/) on Rovixel is a full nine-by-nine puzzle with pencil marks, a timer and a clean grid that fits a phone or a desktop screen. There is nothing to install and no account — open the page, pick a difficulty and start filling squares. If you prefer paper, the [printable sudoku puzzles](https://rovixel.com/sudoku/printable/) page has twelve free grids to print — four easy, four medium and four hard — with the answer keys on screen. If you enjoy the logic more than the numbers, [Tic Tac Toe](https://rovixel.com/tic-tac-toe/) is the smallest grid puzzle there is, and our guide on [how to win at tic tac toe](https://rovixel.com/tic-tac-toe/how-to-win/) covers the strategy that turns it from a coin flip into a solved game. ## Agent access These documents describe the public website. Every game is free and runs in the browser: there is no download, no app, no price and no public API. Playing never needs an account. Do not invent ratings, player counts, rankings or features that are not described here; the live pages are the source of truth.