Sudoku needs no math and no luck, just careful thinking and a little patience. You fill a grid with the numbers 1 to 9 so that none repeats, and every puzzle has one answer you can reach by logic alone. Each puzzle here is made fresh when you ask for it, and its level depends on the reasoning it takes to solve, not just on how many numbers it starts with.
Sudoku rules
- The grid has 81 squares, in 9 rows and 9 columns, divided into 9 boxes of 3 by 3.
- Some squares already hold a number. These are fixed and cannot be changed.
- Fill every empty square with a number from 1 to 9.
- Each row, each column and each box must contain every number from 1 to 9 exactly once.
- The puzzle is solved when the grid is full and no number repeats. Every puzzle has exactly one solution.
How to play on this page
- Choose a level. A new puzzle appears right away, and the timer starts.
- Tap or click a square, then tap a number on the pad. On a computer you can type instead, and move around with the arrow keys.
- Not sure yet? Turn on Notes to pencil in the numbers a square could hold. When you write a number, it disappears from the notes of every square it rules out.
- Use Undo and Redo to step through your moves, and Erase to clear a square.
- Stuck? A hint fills in one correct square. You get three for each puzzle.
- The square you pick lights up along with its row, column and box, and so does every copy of its number. Your game, your options and your best times are saved in this browser.
What the levels mean
Every puzzle is solved by a built-in solver that reasons as a person would, using the simplest method that works. The hardest method it cannot do without sets the level. No puzzle at any level needs guessing.
- Easy: only singles. There is always a square with one possible number, or a number with one possible square.
- Medium: adds locked candidates and pairs, where you narrow down a number's place before you can write it.
- Hard: adds triples, quads, X-Wings and XY-Wings, where you have to compare several rows, columns or squares at once.
- Expert: adds Swordfish, Jellyfish, XYZ-Wings, coloring and chains, where you follow a line of reasoning across the whole grid.
Tips for solving
- Start with the number that appears most often. It has the fewest places left, so it is the quickest to pin down.
- Scan one box at a time. For each missing number, use the rows and columns around the box to rule out squares.
- Look for rows, columns and boxes with only one or two gaps. They are the easiest to finish.
- Keep your notes up to date. When two squares in a row can each hold only the same two numbers, those numbers can be crossed off everywhere else in that row.
- Never guess on the harder levels. If you are stuck, there is a pattern you have not spotted yet, so look at a different number.
Frequently asked questions
- Do I need to be good at math to play Sudoku?
- No. There is no adding or multiplying. The numbers could just as well be nine different symbols, because all that matters is that none repeats.
- Does every puzzle have only one solution?
- Yes. Each puzzle is checked by computer before you see it, so there is exactly one correct answer, and you can reach it by logic with no guessing.
- Where do the puzzles come from?
- Your own browser makes them, using the code on this site. It fills a random grid, then removes numbers as long as the puzzle stays solvable at the level you chose. They are not copied from a book or another site, so you are very unlikely to see the same one twice.
- What happens when I use a hint?
- A hint fills in the square you picked with its correct number, or the most useful empty square if you did not pick one. You get three for each puzzle. Undoing a hint takes the number back out but does not return the hint, and a puzzle solved with a hint does not count toward your best time.
- What does "Show mistakes" do?
- With it on, a wrong number turns red as soon as you write it. With it off, nothing is marked, and you are told only when the grid is full but not yet correct. Your best time counts either way.
- Will I lose my game if I close the page?
- No. Your puzzle, notes, undo history, timer, options and best times are saved in this browser, so everything is still there when you come back. They are not sent anywhere, and clearing your browser data removes them.
- Do I need to download anything or sign up?
- No. The game runs in your browser on a computer, tablet or phone. There is nothing to install and no account to create.