How to play Sudoku
Sudoku is a number puzzle played on a 9 by 9 grid. The grid is split into nine boxes of 3 by 3 squares, outlined with thick lines. Some squares start with a number. Your job is to fill in the rest.
The rules
- Every row must contain the numbers 1 to 9, each exactly once.
- Every column must contain the numbers 1 to 9, each exactly once.
- Every 3 by 3 box must contain the numbers 1 to 9, each exactly once.
That is all. There is no math involved; the numbers could just as well be letters or colors. Every puzzle here has exactly one solution, and you can reach it by logic alone.
How to use this page
- Pick a puzzle. Choose Random puzzle for a new grid any time, or Daily puzzle for the one everyone gets today. Then pick Easy, Medium, Hard or Expert.
- Select a square by tapping or clicking it. Its row, column and box light up, and every copy of the same number is highlighted.
- Enter a number with the number pad or your keyboard. The small number under each key shows how many of that digit are still missing. Tap the same number again or press Erase to clear a square.
- Use Notes to pencil in small candidate numbers while you think. When you place a number, it is removed from the notes in the same row, column and box.
- Get unstuck with Undo, Check (shows any wrong squares) or Hint (fills in one square and adds to your hint count).
The clock pauses when you press Pause or switch tabs, and your game is saved, so you can close the page and pick it up later. When you finish, press Share to copy your time and send it to a friend or post it for your class.
Tips for beginners
- Look for the busiest areas first. A row, column or box with many numbers already filled has the fewest choices left.
- Scan for one number at a time. Pick a digit, say 7, and check each box that is missing it. If the other 7s rule out every square but one, that is where it goes.
- Find the only number that fits. If a square already sees eight different digits in its row, column and box, the ninth digit is the answer.
- Use notes for pairs. If two squares in a box can only be 3 or 8, those two numbers are taken, and you can cross 3 and 8 off everywhere else in that box.
- Never guess. If you are unsure, add notes and look elsewhere. A wrong guess can spread through the whole grid.
Questions
Is every puzzle solvable?
Yes. Each puzzle is made fresh in your browser and checked by a solver before you see it, so it has exactly one correct answer and never needs guessing between two finished grids.
What makes Hard and Expert harder?
They start with fewer numbers, and they need more advanced reasoning. Easy and Medium can be solved by finding singles. Hard needs pairs and lines like the tips above, and Expert may need longer chains of what-if thinking.
How does the daily streak work?
Solve any of the four Daily puzzles to count the day. Solve one again tomorrow and your streak grows by one. Miss a day and it starts over. The streak is saved in this browser only.
Do hints or mistakes stop the game?
No. Hints fill in one square and mistakes are only counted, so you can always finish. Turn off Count mistakes if you would rather not see them.
Is Sudoku good for students?
It is a quick, screen-friendly brain break that practices logic, patience and checking your work. A five to ten minute Easy puzzle between study sessions is a good way to rest without losing focus.