Sudoku

How to play Sudoku

1. The rule. Each row, each column and each of the nine 3×3 boxes must contain the digits 1 to 9 exactly once. That’s the only rule; no maths needed.
2. Pick a cell. Click or tap an empty cell, or move with the arrow keys. Its row, column and box are shaded so you can see what it must not repeat.
3. Fill it. Type a digit or press a button below the grid. A digit that breaks the solution is underlined in red, so you can learn as you go.
4. Take notes. Turn on Pencil (or press P) to jot small candidate digits in a cell. When you place a digit, it’s cleared from the notes of the cells around it.

Where to start on any puzzle

• Scan for the busiest digit. Find the digit that’s already placed most often, then look at each box that’s missing it. Often only one cell in that box can take it.
• Find the cell with one option. When a cell’s row, column and box already hold eight different digits between them, the ninth is the answer.
• Use pencil marks on hard puzzles. Write every candidate in a box or row, then look for two cells that share the same two candidates: those two digits can be removed from every other cell in that unit.
• Don’t guess. Every puzzle here can be solved by logic alone. If you’re stuck, pencil in the candidates for one box and look again.

Learn the five techniques that solve most puzzles in Sudoku for beginners on the Hunt blog.

Levels

Easy starts with about 40 digits and can be finished with simple scanning. Medium has about 32 and usually needs a few notes. Hard has about 27 and rewards careful candidate work. Each new puzzle is made in your browser, and your fastest time for each level is saved on your device only.