Sudoku

How to play Sudoku

The board is a 9×9 grid split into nine 3×3 boxes. Some cells start with a number. Your goal is to fill every empty cell so that:

• each row contains the numbers 1 to 9 once,
• each column contains the numbers 1 to 9 once,
• each 3×3 box contains the numbers 1 to 9 once.

There's no math involved: the numbers are just nine different symbols. Every puzzle here has a single solution that you can reach by logic alone, without guessing.

Using the controls

1. Tap a cell (or move with the arrow keys) to select it. Its row, column and box light up, along with every copy of the same number.
2. Tap a number on the pad, or type it, to fill the cell.
3. Turn on Notes to jot small candidate numbers in a cell instead. Placing a number clears that number from the notes in the same row, column and box.
4. Use Undo to step back, Erase to clear a cell, and Hint to reveal one correct number (three per game).
5. Switch on Highlight mistakes if you want wrong numbers marked in red as you go, or leave it off for a purer challenge.

Your game saves itself after every move. Close the page and it will be waiting for you, timer included.

Strategies that solve most puzzles

• Scan for singles. Pick a number and look at where it already sits. Often the rows and columns it blocks leave only one free cell for it in a box.
• Find the only number that fits. Look at one empty cell and rule out every number already in its row, column and box. If one candidate remains, that's the answer.
• Use notes on hard grids. When scanning stops working, note the candidates in a box or row. Patterns appear: two cells that can only hold the same two numbers, for example, rule those numbers out everywhere else in that unit.
• Work where it's crowded. Rows, columns and boxes that are nearly full have the fewest options and usually give way first.
• Never guess. If you're stuck, there is always a logical step somewhere. Take a fresh look at a different number.

Difficulty levels and the daily puzzle

Easy puzzles have many starting numbers and can be solved by simple scanning. Medium asks for more careful elimination. Hard and Expert grids start with far fewer clues and usually need notes and pairs to crack.

The daily puzzle is the same for everyone on a given day, so you can compare times with friends. It changes at midnight, your local time.

Questions and answers