Free Sudoku: Play Online, No Sign-Up
SudokuTap a square, then a number. Turn Notes on to pencil in small candidates. On a keyboard: arrow keys to move, 1 to 9 to fill, Backspace to clear, N for notes, Z to undo, H for a hint, P to pause.
How to play
How to play Sudoku
- Fill every square. The board is a 9 by 9 grid split into nine 3 by 3 boxes. Some squares already have a number. You add the rest.
- Use each number once. Every row, every column and every 3 by 3 box must contain the numbers 1 to 9 exactly once.
- Work it out, don’t guess. Every puzzle here has exactly one solution, so there is always a square you can fill by logic. Look for a number that can only go in one place in a row, column or box.
- Use notes for candidates. Turn Notes on and tap numbers to pencil in what could go in a square. When you place a number, it is cleared from the notes of the squares that can see it.
- Finish with the fewest slips. A number that is wrong is marked in red and counted as a mistake. Fewer mistakes and no hints earn more stars.
Ways to play
- Four levels. Easy, Medium, Hard and Expert. The fewer numbers you are given, the harder it generally is. Each puzzle is made fresh in your browser, so you never run out.
- Daily Sudoku. One puzzle a day that is the same for everyone, new at midnight UK time. Share your time with friends and compare.
- Challenge a friend. After a puzzle, send the link. Your friend gets exactly the same grid and sees whether they beat your time.
- Pause and come back. The clock stops when you press Pause or leave the tab, and your game is saved on your device so you can carry on later.
At a glance
Altto Sudoku: quick facts
A free online Sudoku game for adults and children, on a computer, tablet or phone.
Updated
- Price
- Free, with no sign-up, no email and nothing to download.
- Levels
- Easy (about 40 numbers given), Medium (about 33), Hard (about 28), Expert (about 24 to 26) and a Daily puzzle that is the same for everyone.
- Solutions
- Every puzzle has exactly one solution, checked as it is made. Nothing needs guessing.
- Helpers
- Pencil notes, undo, erase, hints, highlighting of matching numbers, a mistake counter and a timer you can pause.
- Your result
- Time, mistakes, hints used and up to three stars, plus your personal best on each level.
- Accessibility
- Play with a mouse, touchscreen or keyboard. Each square is read out to screen readers, and animations are turned off if your device asks for less motion.
- Privacy
- Runs in your browser. Your bests, settings and a game in progress are saved only on your device. Nothing is uploaded.
Scoring
How do the stars work?
You earn stars for how cleanly you solved the puzzle. Your time is shown on every result and your personal best is kept for each level, but the stars don’t depend on speed, so you can take your time.
| Stars | Hints used | Mistakes |
|---|---|---|
| ★★★ | None | 2 or fewer |
| ★★ | 2 or fewer | 5 or fewer |
| ★ | Any | Any |
A time only counts as a personal best if you didn’t use a hint.
Tips for solving Sudoku
- Scan for the number with most clues. If a number already appears in six or seven places, look for where its last squares must go.
- Look for the only place. If a number can only fit in one square of a row, column or box, it goes there, even if that square could also hold other numbers.
- Look for the only number. If a square can only hold one number because every other number is already in its row, column or box, fill it in.
- Use notes when you get stuck. Pencil in the candidates for a few squares. Two squares in a box with the same two candidates mean those two numbers can’t go anywhere else in that box.
- Don’t guess. If you are stuck, take a hint rather than guessing: there is always a logical next step, and a hint shows you where to look.
Where does Sudoku come from?
The modern puzzle was first published in the United States in 1979 as “Number Place”, and became popular worldwide after a Japanese publisher called it Sudoku. A Sudoku needs at least 17 given numbers to have a single solution, which was proved by computer search in 2012.
Sources
- Sudoku (Wikipedia): the rules, the history of Number Place and Sudoku, and the 17-clue minimum for a unique solution.
FAQ
Frequently asked questions
Is this Sudoku free?
Yes. Every level, the Daily Sudoku and friend challenges are free, with no sign-up, no email and nothing to download. You see your full result the moment you finish.
How do you play Sudoku?
Fill the 9 by 9 grid so that every row, every column and every 3 by 3 box contains the numbers 1 to 9 exactly once. Some squares are given at the start. Tap a square, then tap a number, or use the number keys on a keyboard.
What are the Sudoku rules?
Each row, each column and each of the nine 3 by 3 boxes must contain every number from 1 to 9 once, with no repeats. The numbers you are given at the start cannot be changed.
Does every puzzle have only one solution?
Yes. Each puzzle is made in your browser and checked so that exactly one solution exists, which means you can always find the next number by logic and never need to guess.
How hard are the levels?
Easy gives about 40 numbers, Medium about 33, Hard about 28 and Expert 24 to 26. The fewer numbers you are given, the harder it generally is. Difficulty also depends on which solving methods you need, so some Hard puzzles feel easier than others.
What is the Daily Sudoku?
One puzzle a day that is the same for everyone, new at midnight UK time. You can share your time with friends. Play it once a day, and use the other levels for as many puzzles as you like.
How do pencil notes work?
Turn Notes on, then tap numbers to pencil small candidates into a square. When you place a correct number, it is cleared from the notes of every square in the same row, column and box. Turn Notes off to fill in numbers again.
What does a hint do?
It fills in one square with the right number, the selected one if it is empty or the first one it can find. Hints are counted and shown on your result, and a time with hints does not count as a personal best.
What counts as a mistake?
Placing a number that is not the one in the finished puzzle. It is marked in red and counted. You can fix it or undo it, but a mistake already made stays on the counter.
How are stars worked out?
Three stars for no hints and two mistakes or fewer, two stars for two hints or fewer and five mistakes or fewer, and one star otherwise. Your time is shown and your best time per level is saved, but stars don’t depend on speed.
Can I pause the game and come back later?
Yes. Press Pause (or the P key) and the clock stops and the board is hidden. The game also pauses if you switch to another tab or app. Your game in progress is saved on your device, so you can close the page and carry on later.
How do I challenge a friend?
After you finish, tap WhatsApp, Messages or Copy link under Challenge a friend. Your friend gets exactly the same puzzle and sees whether they beat your time.
Is Sudoku good for your brain?
It is a fun way to practise concentration and logical thinking, and most people get faster with practice. There is no proof that puzzles on their own prevent memory decline, so enjoy it as a pastime.
Can I play with a keyboard or a screen reader?
Yes. Use the arrow keys to move between squares, 1 to 9 to fill a number, Backspace to clear, N for notes, Z to undo, H for a hint and P to pause. Each square is announced with its row, column and value, and animations are off if your device asks for less motion.
Can I play on my phone or tablet?
Yes. It works on any phone, tablet or computer, with a number pad under the board. Nothing needs installing, and you can add Altto Tests to your home screen if you like.
Is anything stored or uploaded?
Sudoku runs in your browser. Your settings, best times, history and a game in progress are saved only on your device. Nothing is sent anywhere.
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