Sudoku rules explained simply
Sudoku is a logic puzzle that needs no arithmetic at all, it is purely about arranging the digits 1 to 9. Once you understand the one basic rule, you can start right away. Here you will find everything from the goal through the controls to points and stars.
The goal of the game
A Sudoku consists of a square grid of 9 by 9 fields, that is 81 cells. Some of them are already filled with digits at the start; these givens are fixed and must not be changed. Your task is to fill all the remaining cells with the digits 1 to 9 so that in the end the whole grid is solved according to the rules. A good Sudoku always has exactly one unique solution, so you never have to guess and can derive every digit logically.
The structure: rows, columns and blocks
The grid is divided in three ways. There are nine horizontal rows, nine vertical columns and nine square blocks of 3 by 3 cells each, separated by the thicker lines. Every single cell therefore belongs at the same time to a row, a column and a block. It is exactly this interplay of the three regions that defines Sudoku: whoever places a digit always affects all three.
The one basic rule
Sudoku has just a single rule: in every row, in every column and in every block, each digit from 1 to 9 must appear exactly once. Everything else follows from that. A digit may never appear twice within these three regions. Across the whole grid, by contrast, each digit appears exactly nine times. If only one digit remains for a cell that is not already in its row, its column or its block, then that is precisely the digit that belongs there.
How you play: the controls
At Sudoku Sagax you first tap or click the cell you want to fill, it gets highlighted, and matching references in its row, column and block are marked along with it. Then you pick the number you want from the number pad. You correct a wrongly placed digit by selecting the cell again and overwriting or erasing the entry. Given cells cannot be changed. The controls are designed for mouse and touch alike, so play stays smooth at the desk as well as on a phone.
Notes and candidates
As soon as it gets trickier, notes help. Instead of placing a big digit, you store several small candidates in a cell, that is all the numbers still possible there. This keeps you on top of things without committing. When a newly placed digit elsewhere rules out a candidate, you cross it off. If only one candidate remains in the end, the cell is unambiguous. This technique is the key to the harder tiers and a good tool for avoiding mistakes from the outset.
Advanced solving techniques →Hints and help
If you ever get stuck, you can ask for a hint when needed instead of guessing. That keeps the flow going, and you learn what to watch out for yourself next time. Help is an offer, not a must: whoever is after the challenge solves entirely without it.
The four difficulty levels
Sudoku Sagax offers four tiers: Easy, Medium, Hard and Extreme. Easy starts with plenty of givens and is ideal for learning the patterns. Medium is the classic balance for everyday play. On Hard and Extreme there are far fewer givens, so notes and techniques like searching for unambiguous cells really pay off. Higher tiers are more demanding, but in return they also award more points.
Points and stars
For every level you solve you earn points; how many depends on the difficulty and the level: harder puzzles give more. On top of that there are one to three stars per level, depending on your solve time and the number of mistakes. Three stars stand for fast, clean solving; the exact time and mistake thresholds depend on the tier. All points add up to your overall total, and that determines your fox rank.
To the 19 fox ranks →How to avoid mistakes
Most mistakes come from haste: whoever types too fast easily overlooks that the digit is already in one of the three units. Use notes early enough instead of relying on your memory; especially on Hard and Extreme this keeps you on top of things. And reach for a hint before you start guessing, because a guessed number often drags a chain of follow-up mistakes behind it.
From the single puzzle to the daily challenge
Besides the levels of the four tiers, there is a daily challenge every day: one puzzle that is the same for everyone and whose difficulty changes with the day of the week. Whoever solves regularly builds a streak and competes on dedicated leaderboards. So over time the simple basic rules turn into a motivating game with progress and comparison.
Try two puzzles free →What makes Sudoku Sagax different
The rules are the same everywhere, the execution is not. Stronger dividing lines set the three by three blocks clearly apart, the digits appear in an elegant serif typeface, and the sound comes procedurally from the Web Audio system, entirely without audio files. On top of that a warm palette of wine, copper and gold. So classic Sudoku is preserved but feels more refined.
Frequently asked questions about the rules
What are the rules of Sudoku?
A Sudoku is a 9×9 grid made up of nine 3×3 blocks. The goal is to fill every cell with the digits 1 to 9 so that each row, each column and each block contains every digit exactly once. Some cells are given and stay fixed. There is no guessing, every digit follows logically from the others.
Can a digit appear twice?
Within a single row, a single column or a single 3×3 block, each digit may appear only once. If a digit appears twice there, the Sudoku is faulty. Across the whole grid, however, each digit appears several times, exactly nine times.
How do I best start a Sudoku?
First look for rows, columns or blocks that already hold many digits: that is where missing numbers are easiest to pin down uniquely. Jot possible candidates into uncertain cells and cross them off one by one. That way you work from the certain toward the difficult.