Sudoku
Freshly generated puzzles at four difficulties, with hints and mistake checking.
Play Sudoku with a fresh, uniquely-solvable puzzle generated every time — choose Beginner, Intermediate, Advanced, or Expert, get a hint when stuck, and check your work as you go. Works full-screen on mobile.
Rules
Fill the grid so that every row, every column and every box contains each number exactly once. On the classic 9 × 9 board that means the digits 1–9 in each row, column and 3 × 3 box. You never need to guess — every puzzle here has exactly one solution that can be found by logic.
Difficulty levels
Harder puzzles start with fewer numbers filled in (called clues). On the 9 × 9 board:
| Level | Starting clues |
|---|---|
| Beginner | about 40 |
| Intermediate | about 32 |
| Advanced | about 26 |
| Expert | about 22 |
Mathematicians proved in 2012 that a 9 × 9 Sudoku needs at least 17 clues to have only one solution.
Solving techniques
- Scan for singles: look at one number, say 5, and check each box. If only one empty cell in a box can hold a 5 without repeating one in the same row or column, it goes there.
- Find the last empty cell: when a row, column or box has only one gap, the missing number is obvious.
- Use pencil marks: on harder puzzles, note the possible numbers for each empty cell, then cross them off as you fill in others.
- Look for pairs: if two cells in a row can only be 3 or 8, those two numbers can't go anywhere else in that row.
New to Sudoku? Start with the 4 Box (6 × 6) board to learn the rules, then move up to the classic 9 × 9.
Where Sudoku comes from
Despite its Japanese name, the modern puzzle was created in the United States: Howard Garns published it as "Number Place" in Dell puzzle magazines in 1979. The Japanese company Nikoli popularized it in the 1980s and gave it the name Sudoku, short for a phrase meaning "the digits must remain single." It became a worldwide craze in 2005 after newspapers in Britain and the US started printing it daily.
Frequently asked questions
Is every puzzle guaranteed to have exactly one solution?
Yes — each puzzle is generated fresh and verified to have a unique solution before it's shown to you, using the same technique real Sudoku puzzle generators use. It's never ambiguous or unsolvable.
What do the board sizes mean?
9 Box is the classic 9×9 Sudoku with digits 1-9 and nine 3×3 boxes. 4 Box is a 6×6 version with digits 1-6, using six 2×3 boxes — a gentler way to learn the rules. 1 Box is a 3×3 mini-puzzle with just digits 1-3 and no separate box rule (rows and columns already cover the whole grid), good for very young kids or a quick warm-up.
How are the difficulty levels different?
Difficulty is based on how many starting numbers ("clues") the puzzle has relative to the board size — fewer clues means more deduction is needed. It's a reasonable approximation rather than an exact science, especially on the smaller boards where there's less room to vary.
What does Hint do?
It fills in the correct number for your currently selected empty cell — or a random empty cell if none is selected — using the puzzle's known solution.
What does Check do?
It highlights any cells you've filled in that don't match the puzzle's solution, without revealing what the correct number actually is.
Is my progress uploaded anywhere?
No — the puzzle is generated and solved entirely in your browser using plain JavaScript. Nothing is sent to a server.
Do I need to be good at math to play Sudoku?
No. Sudoku uses numbers only as symbols — there's no adding or multiplying. It's a logic puzzle, and you could play it just as well with letters or colors.