--- title: "Sudoku rules: how to play and how to solve, step by step" description: "Sudoku rules in three sentences and how to solve: scanning, naked singles, pencil marks and pairs. Play sudoku free in your browser." url: https://games.klyo.pl/rules/sudoku/ canonical: https://games.klyo.pl/rules/sudoku/ type: zasady language: en author: klyo organization: Klyo Illia Krasnopolskyi (NIP 7822656871), Łódź, Poland contact: kontakt@klyo.pl updated: 2026-10-18 llms: https://games.klyo.pl/llms.txt --- # Sudoku rules Sudoku is a puzzle on a 9 by 9 grid divided into nine 3 by 3 boxes. You fill in the digits 1 to 9 so that each appears exactly once in every row, every column and every box. There is no maths involved, only logic. [Play sudoku](https://games.klyo.pl/sudoku/) [All game rules](https://games.klyo.pl/rules/) - [![Sudoku: gra w przeglądarce od twórcy Klyo](https://games.klyo.pl/foto/zrzut-gra-sudoku-2-800.a31ff905.webp) 5–15 minutes **Sudoku** Sudoku 5–15 minutes portrait & landscape Free online sudoku: 6 levels, hints that teach and a daily challenge.](https://games.klyo.pl/sudoku/) ## In short 1. A 9 by 9 grid with nine 3 by 3 boxes. 2. Each digit 1 to 9 once in every row, column and box. 3. The starting digits stay where they are. 4. A good sudoku has one solution and needs no guessing. 5. No maths needed, the digits are only symbols. ## What are the rules of sudoku? There are three rules. Every row contains the digits 1 to 9 exactly once. Every column contains them exactly once. Each of the nine 3 by 3 boxes contains them exactly once too. The starting digits stay where they are, and you fill in the empty squares. A well made sudoku has exactly one solution. *A highlighted row, column and 3 by 3 box: in each of them every digit from 1 to 9 can appear only once.* ## Do you need to be good at maths for sudoku? No. The digits are only symbols here: letters or colours would work just as well. Nothing is added or multiplied; all that matters is that each symbol appears once in every row, column and box. ## How do you start solving a sudoku? Take the digit that appears most often on the grid and look at the boxes that still miss it. Rows and columns that already hold that digit rule out more squares, so often only one square is left in the box. This is scanning, the first and most important technique. - Naked single: a square where only one digit still fits, because all the others already appear in its row, column or box. - Hidden single: a digit that fits in only one square of a row, column or box, even though that square has other candidates too. ## What should you do when you get stuck in sudoku? Write small pencil marks in the empty squares: the digits that can still go there. Then look for two squares in the same row, column or box with the same pair of candidates: those two digits must go exactly there, so you can remove them from the other squares of that group. Do not guess. A good sudoku can always be finished by logic, and guessing ends with hunting for a mistake across the whole grid. ## What levels does sudoku on klyo have? Six: Easy (40 given squares), Medium (34), Hard (29), Expert (26), Master (24) and Extreme (22). The level comes from the technique the grid really needs, not only from the number of empty squares. There is also a daily sudoku: one grid for every player for the whole day. When you get stuck, the hint shows the next logical step instead of the finished digit. ## How do you solve a hard sudoku step by step? - First scan for each digit in turn, starting with the most common one. - Then pencil marks: write the candidates in every empty square and update them after each digit you place. - Naked and hidden singles in every row, column and box. - Pairs and triples: naked (the same candidates in two or three squares) and hidden (digits that fit only in those squares). - Pointing pairs and box line reduction, then X-Wing, Swordfish and XY-Wing described below. ## Advanced sudoku techniques: X-Wing, Swordfish, XY-Wing When the simple moves run out, patterns that span several groups decide the grid: - Pointing pair: if the candidates for a digit in a box all lie in one row or one column, remove that digit from the rest of that row or column outside the box. - Box line reduction: if the candidates for a digit in a row all lie in one box, remove it from the other squares of that box. - X-Wing: a digit has exactly two possible squares in each of two rows, in the same two columns. It must sit in those rows within those columns, so you remove it from the other squares of both columns. - Swordfish: the same pattern for three rows and three columns. - XY-Wing: a square with candidates A and B sees two squares, one with A and C, the other with B and C. Whichever digit goes in the first square, C ends up in one of the other two, so remove C from squares that see both. ## The most common mistakes in sudoku - Guessing instead of logic: one wrong digit spoils the whole grid and is hard to find later. - Stale pencil marks: after every digit you place, remove it from the candidates in its row, column and box. - Checking only rows and columns and forgetting the 3 by 3 boxes. ## Play Sudoku for free You know the rules, now play. Sudoku runs free in your browser, on a phone and a computer, with nothing to install and no account. [Play sudoku](https://games.klyo.pl/sudoku/) [![Sudoku: gra w przeglądarce od twórcy Klyo](https://games.klyo.pl/foto/zrzut-gra-sudoku-2-800.a31ff905.webp)](https://games.klyo.pl/sudoku/) ## Similar free games - [![Warcaby: gra w przeglądarce od twórcy Rasalhague](https://games.klyo.pl/foto/zrzut-gra-warcaby-800.6e0f6f8e.webp) 5–15 minutes **Checkers** Puzzle 5–15 minutes Checkers against the computer, hotseat and online.](https://games.klyo.pl/checkers/) - [![Saper: gra w przeglądarce od twórcy Klyo](https://games.klyo.pl/foto/zrzut-gra-saper-800.c60de309.webp) new 1 to 5 minutes **Minesweeper** Puzzle 1 to 5 minutes portrait & landscape Classic Minesweeper in your browser: clear the board and flag the mines.](https://games.klyo.pl/minesweeper/) - [![Mahjong Sanctuary: gra w przeglądarce od twórcy Klyo](https://games.klyo.pl/foto/zrzut-gra-mahjong-sanctuary-800.e8ff51f5.webp) 5–15 minutes **Mahjong Sanctuary** Mahjong 5–15 minutes portrait & landscape Free Mahjong Solitaire online: 144 tiles, hints, undo and a daily board.](https://games.klyo.pl/mahjong-sanctuary/) - [![Pasjans Pająk: gra w przeglądarce od twórcy Klyo](https://games.klyo.pl/foto/zrzut-gra-pasjans-pajak-800.057ae24f.webp) 5–15 minutes **Spider Solitaire** Solitaire 5–15 minutes portrait & landscape Free Spider Solitaire online: 1, 2 or 4 suits and a daily deal.](https://games.klyo.pl/spider-solitaire/) ## Rules of other games - [Chess rules](https://games.klyo.pl/rules/chess/) - [How to play solitaire](https://games.klyo.pl/rules/solitaire/) - [How to play Minesweeper](https://games.klyo.pl/rules/minesweeper/) - [Checkers rules](https://games.klyo.pl/rules/checkers/) - [How to win at Tic Tac Toe](https://games.klyo.pl/rules/tic-tac-toe/) - [Mahjong rules](https://games.klyo.pl/rules/mahjong/) - [Castling in chess](https://games.klyo.pl/rules/chess/castling/) - [En passant](https://games.klyo.pl/rules/chess/en-passant/) - [Stalemate in chess](https://games.klyo.pl/rules/chess/stalemate/) - [Chess openings for beginners](https://games.klyo.pl/rules/chess/openings/) - [Spider Solitaire rules](https://games.klyo.pl/rules/spider-solitaire/) - [FreeCell rules](https://games.klyo.pl/rules/freecell/) --- Source: https://games.klyo.pl/rules/sudoku/ · Built and run by klyo, a Polish technology company (Łódź) · Contact: kontakt@klyo.pl · Index for language models: https://games.klyo.pl/llms.txt