How to play sudoku
Sudoku is a logic puzzle played on a 9×9 grid split into nine 3×3 regions. Some cells come pre-filled (the givens) and your goal is to complete the rest using reasoning alone: no maths required.
It's a game for every age that doesn't depend on language or culture — the same rules apply to any board in the world. On Sudokito you can play for free in your browser, with four difficulty levels and nothing to install.
The rules of sudoku
- Every row must contain the digits 1 to 9 with no repeats.
- Every column must contain the digits 1 to 9 with no repeats.
- Each of the nine 3×3 regions must contain the digits 1 to 9 with no repeats.
- A well-formed sudoku has a single solution reachable by logic alone: you never have to guess.
How to play on Sudokito
- Pick a difficulty. Choose easy, medium, hard or expert. Each level keeps its own game in progress, so you can switch back and forth without losing your work.
- Select a cell. Tap or click an empty cell, or move between cells with the arrow keys. The active cell is highlighted along with its row, column and region.
- Enter a number. Type a digit from 1 to 9 with the keyboard or the on-screen number pad. If the number repeats another in the same row, column or region, it's flagged as a conflict.
- Pencil in candidates with notes. Turn on notes mode (the N key) to jot down the possible candidates for a cell in small print, just like pencil marks on paper, before committing to a final digit.
- Fix mistakes and finish. Erase a cell or use undo to step back. When the grid is complete and correct, Sudokito celebrates and saves your best time for that difficulty.
Basic solving techniques
- Scanning
- Sweep rows, columns and regions looking for the only place a digit can go. Start with the areas that already have the most numbers — they resolve first.
- Naked single
- If only one number can go in a cell —because every other digit already appears in its row, column or region— that's its certain value. It's the most direct move.
- Hidden single
- Sometimes a digit can only fit in one cell within a row, column or region, even if that cell allows other candidates. That's where it goes, with no doubt.
- Naked pairs
- If two cells in the same unit share exactly the same two candidates, those two numbers can't sit in any other cell of that unit: remove them from the rest.
Practise these techniques step by step
Frequently asked questions
Do you need to be good at maths to play sudoku?
No. Sudoku is a logic game, not an arithmetic one: the numbers are just symbols and are never added or multiplied. Swap them for letters or colours and the game would be exactly the same.
How many solutions does a sudoku have?
A well-built sudoku has a single solution reachable by reasoning alone. If a board allows more than one solution, it's flawed. Every board on Sudokito has a verified unique solution.
What makes an easy level different from an expert one?
Difficulty isn't about how many clues the board starts with, but the techniques needed to solve it. Easy levels fall to direct logic; expert ones chain several advanced techniques together.
What are notes or candidates?
They are small numbers you write inside a cell to remember which digits could go there, just like pencil marks on paper. They help you reason without committing to a final value yet.
Can I play sudoku for free without signing up?
Yes. On Sudokito you play for free right in your browser, with no downloads and no account. Your game and best times are saved on your own device.