Sudoku9x9.com was launched in 2009. Since then, it has become a place for many loyal users to spend their leisure time every day. Solving a few Sudoku puzzles or completing our daily Sudoku puzzles becomes their daily routine, and this is the motivation for us to make our website better.

What you can do on our website:

1. Learn Sudoku solving techniques and improve your Sudoku solving skills;
2. Play Sudoku games with billions of puzzles of various difficulties from our database on our unique, feature-rich interface;
3. Use our unique, feature-rich interface to play Sudoku puzzles you find elsewhere; and
4. Get help from our smart Sudoku solver to solve any valid Sudoku puzzles in the world with step by step explanations.

Learning Sudoku Solving Techniques

We offer a complete set of Sudoku solving techniques. You can learn various solving techniques and the logic behind them. Also, you will know how to spot the patterns and apply the techniques in real cases.

A unique and very powerful Sudoku solver that can solve any valid Sudoku puzzle is provided on our website. Unlike other common Sudoku solvers, it not only gives the solution to each valid Sudoku puzzle instantly, but also explains the techniques and logic behind each step and how the digit to be filled in each empty cell is determined. This unique Sudoku solver can help you understand and learn Sudoku solving techniques through countless examples. It will effectively improve your Sudoku solving skills, and eventually you can solve all difficult Sudoku puzzles using only logic.

Playing Sudoku Puzzles of Various Difficulties from Our Database

Our website offers billions of Sudoku puzzles, ranging from kindergarten to graduate level, so no matter what Sudoku solving skills you have, you can find Sudoku puzzles with a suitable difficulty level on our website to play with. In addition to the puzzles in our original database, we provide a new puzzle for each difficulty level every day on our "Daily Sudoku" section so that you are guaranteed to have a fresh puzzle to play with on a daily basis.

There is an "Expert Area" on our website. This area is set up for those who have mastered advanced Sudoku solving techniques. The puzzles provided in that area are extremely difficult to solve. So if you have the skills, patience, and time, you can challenge those expert level puzzles.

All puzzles provided by our website have been verified to be valid puzzles (having only one solution) before we put them into our database. So rest assured that you will not encounter a puzzle that has more than one solution or no solution on our website.

In order to help our users focus on solving Sudoku puzzles with logic, our Sudoku game interface is equipped with a variety of user-friendly features, including:

• Pencil marks: This allows you to fill in the empty cells with possible candidate digits. It can also help to observe the patterns for certain Sudoku solving techniques.

• Check mistakes/violations: When solving a Sudoku puzzle, you may sometimes encounter a situation where you cannot continue. It may be caused by a cell filled in with an incorrect digit in a previous step. At this time, our "Check mistakes" function can point out those incorrect cells and let you make the correct decision again.
• Undo/Redo function: If you find that you have entered a step incorrectly, you can use the undo function to return to the step before the error and then continue to solve the puzzle from there. In other cases, you may use the undo function to return to a certain step in the process and then use the redo function to restore each step and confirm the accuracy of each step by yourself.
• Highlight a cell: This allows you to make a note of a cell by highlighting the cell with a choice of color. It is particularly helpful when you try to apply some advanced Sudoku solving techniques such as "coloring", "forcing chain" and "Nishio".
• Save function: Allows you to save a half-finished puzzle and restore the puzzle later within seven days. So you will not lose your work when you have to leave our website in the middle of a game.
• Sometimes you encounter a very difficult puzzle and feel that you cannot solve it, even though every step you have taken looks correct. You want to know what you may have missed or how to use logic to solve this puzzle step by step. There is a "How to solve this puzzle" button on our interface to let you bring up our unique smart Sudoku solver for the current puzzle you are playing. It can solve the current puzzle step by step with explanations and the logic behind it, so that you may learn which step or what skills and logic you may have missed.
• Other functions include one-click to input all candidate digits, one-click to restart the game, one tap on the cell to enter or delete a single candidate digit, and more. Please refer to our manual for all functions in detail.

All these functions combined make it easier for our users to concentrate on applying Sudoku solving techniques and logic to solve Sudoku puzzles, and they also make our Sudoku game interface one of the best choices on the web.

Using Our Interface to Play Your Own Sudoku Puzzles

As our Sudoku game interface has so many features that can make it easier for you to solve Sudoku puzzles, you may ask if you can use our interface to play Sudoku puzzles found in other places, such as newspapers and magazines. The answer is yes. We provide an online Sudoku blank grid. You only need to fill in your own valid Sudoku puzzle, and we will embed your puzzle into our Sudoku game interface. All features on our interface, such as "Check mistakes", "Save" a half-finished puzzle, and others, can be used without any problems. That means you can play any valid Sudoku puzzles found anywhere in the world on our Sudoku game interface, as long as you have a way to find the puzzles.

Getting Help from Our Smart Sudoku Solver

It is not uncommon that you may get stuck in the middle of solving a Sudoku puzzle and want to know the solution or the step by step solution with an explanation for each step. Our smart Sudoku solver can serve this purpose. It not only gives the solution to each valid Sudoku puzzle instantly, but also explains the techniques and logic behind each step and how the digit to be filled in each empty cell is determined. The fact that it can help you understand and learn Sudoku solving techniques through countless examples makes it different from other common Sudoku solvers on the web.

We hope that our website is a good place for you to enjoy the fun of solving Sudoku puzzles and, at the same time, improve your Sudoku solving skills. This is our purpose for building this site. We hope you like it.

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