Sudoku

About Classic Sudoku

Sudoku is a globally popular number-placement puzzle game. It requires no complex mathematics, relying entirely on logical deduction, making it an excellent brain workout and a great way to improve concentration. Whether you want to relax your mind during your free time or push the limits of your logical thinking, playing free online Sudoku offers the ultimate puzzle-solving joy.

Basic Rules & How to Play

A standard Sudoku board consists of a 9x9 grid, divided into nine 3x3 subgrids (blocks). Your objective is to fill the empty cells with digits from 1 to 9, satisfying the following three conditions simultaneously:

• Each Row: Must contain all digits from 1 to 9 exactly once, with no repetitions.
• Each Column: Must contain all digits from 1 to 9 exactly once, with no repetitions.
• Each 3x3 Block: Must contain all digits from 1 to 9 exactly once, with no repetitions.

Advanced Solving Strategies

To become a Sudoku master, basic intuition is often not enough. Here are a few advanced solving techniques you can practice using our in-game \"Notes\" feature:

• Naked Single: If a cell is surrounded by 8 different numbers in its row, column, and block, the only remaining number must be placed in that cell.
• Hidden Single: Within a specific row, column, or block, if a number can only be placed in one specific cell (because all other empty cells are blocked by the same number in intersecting rows/columns), it must be placed there.
• Naked Pairs: If two cells in the same row, column, or block contain exactly the same two candidate numbers, those numbers must occupy those two cells. You can safely remove these two candidates from all other cells in that unit.

Innovative Features on X-Game

We provide more than just the traditional solo training mode (featuring four difficulty levels from Beginner to Expert, all guaranteed to have a unique solution). We have pioneered Real-time Multiplayer PK Modes:

• Speed Mode: Invite friends to a room where everyone faces the exact same puzzle board. Race against time to see whose logic and speed are superior. The first to 100% correctly solve the puzzle wins!
• Steal Mode: All players share the exact same board. You gain points for correct placements, but incorrect placements will result in a time-freeze penalty. It transforms a solitary puzzle into an adrenaline-pumping competitive arena.

Ready for the challenge? Select a difficulty above and let the brainstorming begin!

FAQ

Is Sudoku free to play?

Yes. Puzzle PK offers classic Sudoku free in your browser with no downloads, no installs, and no hidden costs. Every difficulty level and both multiplayer modes are included, whether you practice solo or compete with friends.

Can I play Sudoku on my phone?

Yes. Sudoku is fully optimized for touchscreens: tap a cell to select it, fill it in with the number pad, and switch on Notes to track your candidates. The grid scales on any screen, and you can join multiplayer rooms from phone, tablet, or desktop.

How do I play Sudoku against other people?

Create a room from the multiplayer lobby and invite friends, or join a public one to face players worldwide. In Speed PK, everyone solves the identical puzzle and the first to complete it correctly wins; in Steal PK, all players share one board, scoring points for correct entries and losing seconds to freezes for mistakes. Both modes work across mobile and desktop.

What difficulty should I start with?

If you are new to Sudoku, start with Easy — the most pre-filled numbers make it easy to learn the row, column, and box rules without getting stuck. Move to Medium once solving feels automatic, and leave Expert for players who already use advanced candidate techniques comfortably.

What is a good time for solving a Sudoku?

As a rough guide, 3 to 5 minutes for Easy, 10 to 15 minutes for Medium, and 20 to 30 minutes for Hard are normal for recreational solvers. Competitive players finish expert puzzles in just a few minutes, so treat speed as a goal, not a requirement — accuracy first, speed later.

Why is my Sudoku stuck — is it unsolvable?

Sudoku never requires guessing: every entry is logically forced, so a dead end almost always means an earlier number is wrong. Every Puzzle PK puzzle has exactly one solution, so a contradiction is a clear sign to backtrack and re-check rows, columns, and boxes. Review the last few numbers you placed and use Notes to track candidates — the error is usually quick to find.