How to Play

The basic rule

Fill each empty cell with a digit from 1 to 9. In every 9x9 grid, each row, each column and each 3x3 box must contain every digit exactly once. The starting numbers are fixed, and a well made puzzle has exactly one solution, so you never need to guess.

Beginner techniques

Scanning. Pick a digit and look across rows and columns where it already appears. Often only one cell in a box is left where it can go.

Last free cell. When a row, column or box has only one empty cell, the missing digit goes there.

Only possible digit. For one cell, rule out every digit already in its row, column and box. If one digit remains, you have found it.

Intermediate techniques

Pencil marks. Turn on Notes and write the possible digits in each cell. Patterns become much easier to see.

Pairs. If two cells in a unit can only hold the same two digits, those digits can be removed from every other cell in that unit.

Pointing. If a digit inside a box can only sit in one row or column, it can be removed from that row or column outside the box.

Advanced techniques

X-Wing. When a digit appears as a candidate in exactly two cells of two different rows, and those cells share the same two columns, it can be removed from the rest of those columns.

Chains. Follow "if this cell is 4, then that one must be 7" through the grid. If a chain leads to a contradiction, the starting guess is wrong.

Puzzle types

Classic Sudoku

  • Fill every empty cell with a digit from 1 to 9.
  • Each row, column and 3×3 box must contain each digit exactly once.

Twin Sudoku

  • Solve two 9×9 grids that share a middle column of three boxes.
  • Each grid has its own nine-cell rows and columns. A row does not extend across all 15 cells.
  • Every shared cell must obey the rules of both grids.

Double Sudoku

  • Solve two 9×9 grids sharing one corner 3×3 box.
  • Every row, column and 3×3 box in each grid contains 1 to 9 exactly once.
  • Both diagonals of the lower-right grid also contain 1 to 9 exactly once.
  • Shared cells obey both grids; empty gaps are not playable.

Samurai Sudoku

  • Samurai Sudoku uses a central 9×9 grid and four outer 9×9 grids.
  • Each outer grid shares a corner 3×3 box with the central grid.
  • Rows, columns and boxes in every grid contain 1 to 9 once; shared cells must satisfy both grids.

Jigsaw Sudoku

  • Fill each row and column with the digits 1 to 9 exactly once.
  • Instead of square 3×3 boxes, use the nine outlined irregular regions.
  • Each irregular region contains nine cells and must also contain 1 to 9 once.

Diagonal Sudoku

  • Follow the standard row, column and 3×3 box rules.
  • Both main diagonals must also contain the digits 1 to 9 exactly once.
  • The centre cell belongs to both diagonals and must satisfy both.

Expert Sudoku

  • Expert describes a difficulty level, not a separate grid shape.
  • Follow the rules of the individual puzzle, including any overlapping regions or diagonals.
  • Use logical deductions to fill every active cell without repeating digits in a required group.

Controls

Tap a cell, then tap a number. Turn on Notes to pencil in candidates. Undo, Redo, Clear, Hint and Reset sit above the number pad, and Check shows any wrong entries. Progress is saved automatically in this browser.

On a keyboard: 1 to 9 to enter, arrow keys to move, N to toggle notes, Backspace to clear, Ctrl+Z and Ctrl+Y to undo and redo.