Sudoku is a logic puzzle on a 9×9 grid. Fill every empty square with a number from 1 to 9 so that each row, each column and each of the nine 3×3 boxes contains every number exactly once. No arithmetic is involved; the numbers could just as well be symbols. Every puzzle here is generated fresh and checked by computer to have exactly one solution, so it can always be solved by logic alone without guessing.
How to play
- Choose a difficulty and press New puzzle.
- Select an empty square by clicking or tapping it.
- Enter a number with the number pad or your keyboard.
- Keep going until the grid is full. A number that breaks the solution turns red and adds to your mistake count.
The bold white numbers are the starting clues and cannot be changed. Numbers you enter appear in blue.
Controls
- Numbers 1 to 9: keyboard or the on-screen pad.
- Move: arrow keys.
- Erase: Backspace, Delete or the Erase button.
- Notes: press N or the Notes button to pencil in small candidate numbers instead of answers.
- Undo: Z or the Undo button.
- Hint: fills in the selected square, or the next square that is still wrong.
When you select a square, its row, column and box are highlighted, along with every other copy of the same number. Your puzzle and time are saved in this browser automatically.
Difficulty levels
Easy puzzles start with 40 clues, medium with 32 and hard with about 26. Fewer clues usually means you need more advanced reasoning to make progress, although the exact difficulty of any single puzzle also depends on where the clues sit. For comparison, mathematicians proved in 2012 that a standard Sudoku needs at least 17 clues to have only one solution.
Solving techniques, from simple to advanced
Scan for the obvious placements
Pick a number, say 5, and look at each 3×3 box that is missing it. Rows and columns that already contain a 5 rule out squares in that box. Often only one square is left, and that is where the 5 goes. Repeat for each number from 1 to 9. On easy puzzles this alone can take you most of the way.
Single candidate
Look at one empty square and list the numbers already present in its row, column and box. If eight different numbers are ruled out, the ninth must go there.
Use notes
On medium and hard puzzles, scanning eventually stops working. Switch on Notes and write the possible numbers into each empty square of a box, row or column. Patterns that are invisible in your head become obvious on the grid, and when you place an answer the game removes that number from the notes of every square it affects.
Naked pairs
If two squares in the same row, column or box both have exactly the same two candidates, for example 3 and 8, those two numbers must go in those two squares. You can remove 3 and 8 from the notes of every other square in that row, column or box.
Pointing pairs
If, inside one box, a number can only go in squares that all sit on the same row, that number must be in that row within the box. You can then remove it from the rest of that row outside the box. The same works for columns.
Common mistakes
- Guessing. These puzzles never require it. If you feel stuck, look for a pair or switch to notes before trying a number at random.
- Forgetting the boxes. New players often check rows and columns but miss a repeat inside the 3×3 box.
- Stale notes. Notes you wrote early can become wrong as the grid fills. Clear and redo them for a box if things stop making sense.
Where Sudoku comes from
The puzzle in its modern form was created by Howard Garns and first published in 1979 in a Dell puzzle magazine under the name Number Place. It took off in Japan after the publisher Nikoli printed it in 1984 and gave it the name Sudoku, and it became a worldwide newspaper puzzle in the mid-2000s. The Sudoku on Gamdie is our own implementation with its own puzzle generator.
Frequently asked questions
Is this Sudoku free?
Yes. It runs in your browser with no download, sign-up or payment, on desktop and mobile.
Does every puzzle have a solution?
Yes, and only one. Each puzzle is checked by a solver before you see it, so logic will always get you to the end.
Do I need to be good at maths?
No. Sudoku only uses the numbers as labels. It is about logic and patience, not calculation.
Will my progress be saved?
Your current puzzle, time and best times are stored in this browser. A private window or clearing your browser data resets them.
