How to Play Sudoku

Basic Rules

The objective of Sudoku is to fill the 9x9 grid with digits from 1 to 9. Each number can only appear once in each row, column, and 3x3 box.

  • Each row must contain the numbers 1-9 with no duplicates
  • Each column must contain the numbers 1-9 with no duplicates
  • Each 3x3 box must contain the numbers 1-9 with no duplicates

Sudoku Terms

Understanding these basic terms will help you learn Sudoku strategies:

Grid
The complete puzzle layout consisting of rows, columns, and boxes.
Cell
An individual square in the grid that can contain a number or notes.
Row
A horizontal line of cells across the grid that goes through multiple boxes.
Column
A vertical line of cells down the grid that goes through multiple boxes.
Box
A sub-section of the grid (also called block or region).
House
Any row, column, or box. Cells share houses if they are in the same row, column, or box.
Candidate
Also known as notes, represents possible values that can still legally occupy a cell.
Fixed Cell
Initial clues that are fixed numbers and can never change.

Using the Play Toolbar

The toolbar below the Sudoku board provides all the tools you need to play. Here's how to use each feature:

Selecting a Cell

Click or tap on any cell in the grid to select it. The selected cell will be highlighted, and toolbar actions will apply to it.

Entering a Number

1. Select the target cell on the board.
2. Click the desired digit on the number pad.
3. The number will be entered in the cell, replacing any notes if "Remove notes" is enabled in preferences.

Clearing a Cell

1. Select the cell you want to empty.
2. Click the Clear button (eraser icon).
3. The cell will be cleared of its value and any note styling.

Entering Notes

1. Activate Note mode by clicking the Notes button (it will glow when active).
2. With a cell selected, click digits on the number pad to add or remove candidate notes.
3. Click the Notes button again to return to normal entry mode.

Starting a New Game

1. Select a difficulty level from the dropdown (Easy to Extreme).
2. Click the New Game button to generate a fresh puzzle at the chosen difficulty.

Lock Mode (Advanced)

Double-click any digit on the number pad to lock it. Then, selecting cells will automatically enter that digit (or toggle notes if in Note mode) until you double-click again or select a different digit.

Solving Tips

Here are some practical tips to help you solve Sudoku puzzles more effectively:

  • Start with singles: Look for cells with only one possible number (naked singles) or numbers that can only go in one cell in a row/column/box (hidden singles).
  • Use elimination techniques: Apply box/line interactions to eliminate candidates from boxes and lines.
  • Look for pairs and sets: Find naked or hidden pairs/triples that limit where certain numbers can go.
  • Progress systematically: Work through techniques in order: singles → interactions → sets → fish → wings → advanced methods.
  • Take notes: Use the notes feature to track possible candidates for each cell.
  • Don't guess: Each move should be logically derived; guessing usually leads to dead ends.

For detailed explanations of advanced solving techniques like X-Wing, Swordfish, and XY-Wing, visit our Algorithms Guide.