Sudoku

How to Play Sudoku

The Rules

Sudoku is a logic-based number placement puzzle played on a 9x9 grid divided into nine 3x3 boxes. The objective is to fill every cell with a digit from 1 to 9 so that each row, each column, and each 3x3 box contains all nine digits exactly once. No digit may repeat within any row, column, or box. The puzzle begins with some cells pre-filled as clues, and the difficulty depends on how many clues are given and which solving techniques are required.

1. Select an empty cell by clicking or tapping it. The cell, its row, its column, and its 3x3 box will highlight to help you see which numbers are already placed.
2. Enter a digit from 1 to 9 using your keyboard or the on-screen number pad. If the number violates a constraint (duplicate in row, column, or box), the conflicting cells will flash to alert you.
3. Use pencil marks to note possible candidates in cells where you are uncertain. Toggle pencil mode with the pencil icon or press P.
4. Continue filling cells using logic. Never guess randomly. Every properly constructed Sudoku puzzle has exactly one valid solution that can be reached through deduction alone.
5. The puzzle is complete when all 81 cells are correctly filled with no constraint violations.

Difficulty Levels

OfficeGames.io generates Sudoku puzzles at four difficulty levels, each verified to have exactly one unique solution. Easy puzzles provide more pre-filled cells (typically 36 to 45) and can be solved using basic techniques like naked singles and hidden singles. Medium puzzles reduce the clue count and may require naked pairs or pointing pairs. Hard puzzles demand techniques like box-line reduction and hidden triples. Expert puzzles are the most challenging, with fewer than 25 clues and requiring advanced strategies such as X-Wing, Swordfish, or chains. The daily Competitive puzzle rotates through difficulty levels throughout the week, so every player faces the same challenge regardless of skill preference.

Tips to Play Better

• Start by scanning the grid for rows, columns, or boxes that are nearly complete. Cells with only one possible candidate are the easiest to fill first.
• Use pencil marks liberally, especially on harder puzzles. Writing down all candidates for each cell helps reveal hidden patterns and eliminates guesswork.
• Look for naked singles: a cell where only one digit is possible because all other digits already appear in its row, column, or box.
• Look for hidden singles: a digit that can only go in one cell within a particular row, column, or box, even if that cell has other candidates.
• Practice the pointing pairs technique. When a candidate in a box is restricted to a single row or column, that candidate can be eliminated from other cells in that row or column outside the box.
• Work systematically through numbers 1 to 9, checking where each can be placed across the grid. This methodical approach prevents you from overlooking easy placements.
• Never guess. If you feel stuck, revisit your pencil marks and look for new eliminations. A well-constructed puzzle always has a logical next step.

Playing Sudoku at OfficeGames.io

OfficeGames.io is designed for professionals who want a focused mental break during the workday. The clean, dark interface makes Sudoku look like a data dashboard from across the room. The timer starts only when you interact with the grid, and pauses automatically when you switch tabs, so your time reflects actual solving effort. Your progress saves automatically, and with a free account your stats sync across devices so you can start on your work laptop and finish on your phone.

Frequently Asked Questions