Sudoku

Fill the grid so every row, column and 3×3 box holds the digits 1 to 9 once. Pick a level, play today's puzzle or generate unlimited new ones.

How to play

1. Tap a cell, then a number. Every row, column and 3×3 box must end up holding 1 through 9 exactly once. The bold black numbers are given and locked; the ones you place are blue.
2. Each number you place is checked against the solution. A wrong one flashes red, does not stay on the board and counts as a mistake, even if it clashes with nothing yet.
3. Mistakes never end the game. Each one costs 100 points and can cost you a star, and the counter next to the timer shows how many you have made. Typing the same wrong number in the same cell again isn't counted twice.
4. Turn on Notes (or press N) to pencil in candidates. When you place a number, that number is crossed out of the notes in its row, column and box.
5. Undo (Ctrl+Z) takes back placements, erases and notes, but never a mistake or a hint. Erase (Backspace) clears a cell.
6. The small number on each key is how many of that digit are still to place. A key greys out once all nine are on the board.
7. On a keyboard: arrows move, 1 to 9 fill, Backspace erases, N toggles notes.

Hints and scoring

You get 3 hints per puzzle. A hint fills the selected cell with its correct number, or, if no empty cell is selected, the empty cell with the fewest possible numbers. Hints are saved with your progress.

Only a solved puzzle scores. Points start at 1000 on Easy, 1500 on Medium, 2000 on Hard and 2500 on Expert, then lose 1 per second, 100 per mistake and 150 per hint, never going below 0. Stars: 3 for a solve with no mistakes and no hints, 2 for at most one mistake and at most one hint, 1 for any other solve.

Levels

Easy starts with about 40 given numbers, Medium about 32, Hard about 27 and Expert 24 to 27. Every puzzle has exactly one solution. Each level has its own daily puzzle and its own statistics, so you can keep an easy streak and a hard streak going at the same time.

Daily or Unlimited?

Daily is the same grid for everyone and counts toward your streak. Unlimited makes a new grid on demand; the link in the address bar reopens that exact puzzle, so you can send a hard one to a friend.

Tips for faster solving

• Start with the number that already appears most often; the pad shows how many of each are left.
• Tap a filled number to highlight every copy of it. Rows and boxes with no highlight are where it still has to go.
• When a cell has only one candidate, fill it. When a number fits only one cell in a box, place it. Most puzzles up to Hard fall to those two moves.
• Expert grids need pairs: two cells in a unit that share the same two candidates lock those digits out of the rest of the unit.