Sudoku
Learn the single rule behind Sudoku and the first two solving techniques, then try them on a built-in 9x9 puzzle with a one-click answer check.
Sudoku
Learn the single rule behind Sudoku and the first two solving techniques, then try them on a built-in 9x9 puzzle with a one-click answer check.
About Sudoku
Built-in 9 by 9 puzzles
Each reset picks one puzzle from the local built-in puzzle list. Given cells are locked, and empty cells accept only digits from 1 to 9; clearing an input returns that cell to blank.
Exact answer check, not a full solver
The Check button compares the whole board with the stored solution for the current puzzle. It does not provide hints, difficulty selection, a Sudoku solver, or live row, column, and box validation while you type.
FAQ
Common questions and answers about this topic.
What are the rules of Sudoku?
A Sudoku board is a 9x9 grid split into nine 3x3 boxes, and there is only one rule to follow. Each digit from 1 to 9 appears exactly once in every row, exactly once in every column, and exactly once in every 3x3 box. A puzzle starts with some cells already filled, and every remaining cell can be worked out from that single rule alone.
Do you need to be good at maths to play Sudoku?
No. The digits are simply nine symbols that have to stay distinct, so replacing them with nine letters or nine colours would leave the puzzle unchanged. You never add, subtract or multiply anything. Solving a Sudoku means ruling out the possibilities that would break the rule until only one option is left.
Where should a beginner start on a new puzzle?
Start where the board is already crowded. A row, column or box with only two or three blanks left offers far fewer possibilities than an empty one. Then take a single digit and check which rows, columns and boxes already contain it, because those lines rule the digit out everywhere they cross. When a box has only one cell left that the digit can legally occupy, you have found a placement. This method is called scanning, and on an easy puzzle it fills in a large part of the board on its own.
Which solving techniques should you learn first?
Two techniques cover most easy and medium puzzles. A naked single is a blank cell where every digit except one has been ruled out, so that digit has to go there. A hidden single is a digit that still fits in only one cell of a particular row, column or box, even when that cell looks like it has several options. The two work from opposite ends, one starting from the cell and the other from the digit, and alternating between them clears a board surprisingly fast. This page has no pencil-mark feature, so write candidates down on paper if you want to track them.
How do you play the puzzle on this page?
The numbers that come with the puzzle are locked and cannot be edited. Click any blank cell and type a digit from 1 to 9, and clearing the input returns that cell to blank. Check compares the entire board with the stored solution for the current puzzle and answers only solved or not solved, so it will not point at the cell you got wrong. Reset draws another puzzle and clears whatever you had filled in.
How many puzzles are there, and can you pick a difficulty?
There are 100 built-in puzzles and Reset picks one of them at random. Every puzzle starts with 41 filled cells and 40 blanks, so the difficulty is the same throughout and there is no difficulty selector. Everything runs in your browser, with nothing to install and no account to create. Progress is not saved, which means reloading the page or pressing Reset starts you on a fresh puzzle.