Free online sudoku
Sudoku is the number puzzle everyone knows: complete the board so that each number appears once in every row, every column and every box. Play right on this page, on a phone or a computer, free and with no sign-up. Pick a level and start.
Every kind of sudoku
How to play sudoku
- The board has 9 rows, 9 columns and 9 boxes of 3×3. Some cells are already filled in.
- Fill every empty cell with a number from 1 to 9.
- The only rule: each number appears exactly once in every row, every column and every bold box.
- No math and no guessing. Every board here has exactly one solution, and you can reach it with logic.
On the board: tap a cell, then a number. ✏️ Notes writes small possibilities, ↩️ undoes a move, and 💡 fills one cell when you are stuck. On a computer you can type numbers, move with the arrow keys, press N for notes and Ctrl+Z to undo.
Tips and strategy
- Scanning: Pick a number, say 5, and check each box for where it can still go. If only one cell is left, that is its place.
- What is missing in a line: Start with a row, column or box that is missing only one or two numbers. Work out which number is missing and where it is allowed.
- Notes (✏️): On the harder levels, write the possible numbers in each cell. When you place a number, it is erased automatically from the notes of its row, column and box.
- Pairs: If two cells in a row can only hold the same two numbers, those numbers belong to them. Remove them from the rest of the row.
- Locked in a box: If a number can go only in one row inside a box, it cannot appear in that row in the other boxes.
- Do not guess: If there is no safe move, look at another number or another area. A wrong guess early on only shows up many moves later.
How is the difficulty decided?
Every board on the site is checked twice. First a computer makes sure it has exactly one solution. Then a solver that works like a person, starting with simple steps and moving to advanced techniques only when it has to, sets the level. Easy and medium need simple steps only (easy has at least 36 clues), hard needs note-based techniques such as pairs, locked candidates or X-wings, and very hard is still stuck after those and needs testing hypotheses.
Stuck on a sudoku from a newspaper or a puzzle book? In the sudoku solver you type in the board and get the solution, plus an answer if the board has no solution or has more than one.
Frequently asked questions
What are the rules of sudoku?
Fill a 9×9 board with the numbers 1 to 9 so that each number appears exactly once in every row, every column and each of the nine 3×3 boxes. That is the only rule. There is nothing to add up or calculate.
Is the sudoku here really free?
Yes, everything is free with no sign-up: online sudoku, the daily sudoku and the sudoku solver.
How is the difficulty set?
Every board is checked by a computer solver that works like a person. Easy and medium are solved with simple steps only (easy has more clues). Hard needs note-based techniques such as pairs and locked candidates. Very hard needs testing hypotheses, because those techniques are not enough.
Does every sudoku have one solution?
Yes. The computer checks each board before it reaches you and makes sure it has exactly one solution, so you can always get there with logic.
Can I play sudoku on a phone?
Yes. The board is made for touch screens: tap a cell, then a number from the row below. On a computer you can type numbers, move with the arrow keys, press N for notes and Ctrl+Z to undo.
Explore more: the sudoku solver, the daily sudoku, and all online games.