Sudoku
Free sudoku in the browser, at six levels. It starts with a 4x4 animal board a four-year-old can finish, and ends with a 9x9 that will hold you for a quarter of an hour.
- Free
- No ads
- No account
- No download
- Works offline
- Single player
How do you play?
- Pick a level - Two rows: animals 4x4 and 6x6 on top, then easy, medium, hard and expert.
- Touch an empty square - It gets selected. That is it.
- Pick a symbol - An animal or a digit, depending on the board. Change it as often as you like.
- Check the row, column and box - If that symbol is already in any of them, it cannot go in again.
- Fill the board - The clock stops, and a record for that level is saved if you beat it.
About this game
One rule, and it never changes between levels. Every row, every column and every box holds each symbol exactly once. That is the whole game.
What changes is how much of the board is already done for you. We ran our generator over 60 boards at each level and counted. On the 4x4 animal board you fill in 7 of 16 squares. On easy you fill 39 of 81. On expert, 56. Same rule. Eight times the work.
Expert then did something we had not expected. We asked the generator to carve down to 24 clues and it managed 24.7 on average, sometimes stopping at 27, because it refuses to remove a clue that would leave the board solvable two different ways. Around 24 clues it starts hitting that wall. The other five levels reach their targets exactly and without effort. So expert is not one more notch on the same scale. It is the point where sudoku itself starts pushing back.
The two small boards use animals rather than digits. Not for cuteness. A four-year-old does not need to know what a 7 is to see that there are two dogs in the same row. Six animals that differ by shape and not only colour, so a child who cannot separate colours still solves the board.
There is a clock and it runs. This is the one game where we chose to measure time instead of moves, because sudoku has no wasted move: either you can prove what goes in a square or you cannot yet. The record is kept per level, because a 4x4 animal board and an expert grid are not the same achievement and there is nothing to gain from comparing them.
What does it teach?
Deduction
Every square is solved by elimination: what cannot go there. That is mathematical thinking with no arithmetic in it.
Working systematically
Jumping around gets you stuck. Scanning in order gets you through. The board teaches that by itself.
Patience
There is no luck here and no shortcut. There is only the next square you can prove.
Pattern recognition
After a few boards the eye starts spotting an almost-full box from across the grid.
Tips
Start where it is crowded
Find the row or box with the most clues already in it. Fewest options left means that is where your first provable move is hiding.
Never guess
A good sudoku always has one square you can prove. If you cannot find it, you have not run out of luck, you have run out of scanning.
Hunt a symbol, not a square
Instead of asking what goes in this square, take one symbol and ask where it can possibly sit in this box. Usually the answer is one place.
Stuck? Count
Every row holds the same set of symbols. See which one is missing, then work out where in the row it can sit.
What age is it for?
4 to 5
The 4x4 animal board. Six animals, 16 squares, 7 to fill. Not a bad first record.
6 to 8
Animals 6x6, then easy. This is where scanning replaces guessing.
9 and up
Medium and hard. The board stops falling out in one pass around it.
Grown-ups
Expert. 56 squares to fill, and you already know the rule.
Accessibility
One tap per action, with no dragging and nothing to hold down. On the children's boards the symbols are animals that differ by shape rather than only by colour, so colour blindness does not get in the way. The grid always gets a true square on screen and is never stretched, including on a phone held sideways. Nothing disappears if you wait, there is no countdown and there is no red screen. The clock is a measurement rather than a pressure: stop in the middle, think for a minute, come back.
Playing together
Who spots it first
Pick one symbol and each of you hunt for where it sits in your own box. Whoever can prove it, plays it.
Say why
Before they touch a square, ask for the reason. A child who can say why it has to be a three has understood the game, even if the next one is wrong.
Clock off
Just ignore it. It gives no grade and it does not run out.
Backwards
Solve a board together, then cover two squares and let them put those back. An easy solve with the same moment of getting it.
Common questions
What age can start playing sudoku?
Four, on the 4x4 animal board. There are no digits on it at all, so a child who does not know numbers yet solves it without any trouble.
Is the sudoku free?
Yes. No payment and no in-game purchases. All 21 games on the site are open from the first second.
How many clues does each level give you?
Counted over 60 boards per level: 9 on animals 4x4, 18 on animals 6x6, 42 on easy, 34 on medium, 28 on hard and about 24.7 on expert. Expert is not exactly 24 because the generator refuses to go below the point where the board would have more than one answer.
Does every board have exactly one solution?
Always. The generator checks that for every clue it removes and puts it back if the board would become ambiguous. You will never be stuck needing a guess.
Do I need to download or sign up?
No. It runs in the browser, with no download and no account.
How is the record measured?
By solve time, where faster is better, and separately for each level. An animal board and an expert grid never compete with each other.
Can I play offline?
Yes. After one visit everything is stored on the device, generator included, so new boards keep appearing with no signal.
Are there ads?
None. No banners, and nothing that plays between levels.
What happens if I get one wrong?
Change the symbol in that square as often as you like. There is no penalty, no score going down, and nobody counting your mistakes.