Play Sudoku Online or Solve a Puzzle
Choose a level and play a fresh puzzle with a unique solution, with notes and hints. Or copy in the grid from your magazine: the tool solves it instantly.
- Free
- 4 levels
- Unlimited puzzles
- Sudoku solver
100% private — Everything is processed directly in your browser: your files, voice, and image are never sent to Chatzam's servers.
How to play sudoku online
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Choose a level
Easy, medium, hard or expert: a new puzzle with a unique solution is generated.
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Fill in the grid
Tap a cell, then a number. Switch to notes mode to pencil in candidates in small digits.
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Get help if you need it
Turn on mistake checking or ask for a hint, which reveals one cell. Your game is saved automatically.
Everything for a comfortable game
Endless puzzles
Each puzzle is generated on demand and always has exactly one solution, in 4 difficulty levels.
Game aids
Notes mode, undo, eraser, highlighting of the row, column, box and matching numbers, mistake checking, hints and a timer.
Solve my puzzle
Copy in a puzzle from a newspaper or magazine: the tool solves it instantly and tells you if it has no solution or several.
Printable A4
Print the puzzle, with or without the solution, to play on paper. Your current game stays saved on your device.
Sudoku rules
A sudoku grid has 81 cells, arranged in 9 rows, 9 columns and 9 boxes of 3 × 3. The goal: place the numbers 1 to 9 so that each one appears only once in every row, every column and every box. A few numbers are given at the start; they can't be changed. A good puzzle has only one solution, which you can reach by logic, without guessing. More given numbers usually means an easier puzzle, but the count isn't everything: difficulty mostly depends on the techniques you need. A puzzle needs at least 17 given numbers to have a unique solution.
Solving techniques: candidates, singles, pairs
Start by writing down the candidates: for each empty cell, the numbers still possible given its row, column and box. That's exactly what notes mode is for. Naked single: a cell has only one candidate left, so you can fill it in. Hidden single: a number can only go in one place in a row, column or box, even if that cell has other candidates. Naked pair: two cells in the same group only accept the same two numbers, for example 4 and 7; those numbers can be crossed out of the other cells in the group. Finally, if within a box a number is only possible in a single row, remove it from the rest of that row.
Solve a puzzle from a newspaper or magazine
Stuck on the newspaper sudoku? Switch to "Solve my puzzle" mode, copy in the given numbers cell by cell, then run the solver: the solution appears instantly. The tool also checks the grid. If it says there's no solution, it's almost always a copying mistake: a number in the wrong place or typed twice. If it says there are several solutions, a given number is probably missing. Double-check the grid row by row before blaming the publisher. To play away from the screen, print any puzzle in A4, with or without the solution, handy for a commute or for an older relative who prefers paper.
Frequently Asked Questions
What are the rules of sudoku?
Fill the 9 × 9 grid with the numbers 1 to 9 so that each number appears only once in each row, each column and each 3 × 3 box.
How do you solve a hard sudoku?
Write down all the candidates for each cell, then look for singles (a cell with only one candidate, or a number with only one possible place) and pairs, which let you eliminate candidates elsewhere.
Can I solve a sudoku online?
Yes: in "Solve my puzzle" mode, copy in the given numbers and the solution appears instantly. The tool also tells you if the puzzle has no solution or several.
How do I print a sudoku puzzle?
Use the print button: the puzzle is laid out in A4 format, with or without the solution, as you choose.
Is my game saved if I close the page?
Yes, your current game is saved automatically on your device. You'll find it again when you come back to the page in the same browser.