Sudoku Free Online - Ultimate Sudoku

sudoku free online
Play HTML5: Medium | Large

Get ready to play Sudoku free online in your browser. This well-made Sudoku online game is a joy to play.

It has advanced features including cell tagging and row/column highlighting. You can choose from three levels of difficulty.

To begin, click one of the links under the picture of the game. This opens the game in a pop-up window.

Note: The HTML5 version is an HTML5 game. It does not require the Adobe Flash Player.

Sudoku Free Online - Instructions

NOTE: The instructions below were written for the Flash version of this game originally. Most of the explanation still applies.

Choose from Easy, Medium, Hard, and Expert levels of difficulty.

You can even make notes right in the sudoku grid when you need to guess between two or more numbers.

If you like this Sudoku free online game, you might enjoy Kakuro and Math Mountain.

Sudoku is a math game. The goal is to find the missing numbers in a 9 by 9 grid by following a few simple rules. The rules may be simple, but solving a sudoku puzzle is always a challenge.

See below for a summary of the rules of sudoku. For detailed instructions, including advanced techniques, visit the Sudoku Instructions page.

HOW TO PLAY. The first screen that displays in this online sudoku game is the difficulty selection screen. Click on the sudoku difficulty you want to try.

Choose between Easy, Medium, Hard, or Expert depending on your skill level. If you've never played sudoku before, choose Easy mode.

The sudoku board consists of a square 9x9 grid. This grid is itself divided into nine 3x3 subgrids.

When you begin, some numbers are provided, but many of the individual squares in the sudoku grid are blank.

You goal in this free Sudoku online game is the same as standard sudoku. Find the one, and only one, correct numeric entry for each blank square in the grid such that all the rules of sudoku are satisfied.

Here are the rules of Sudoku:

  • Each row must contain the numbers 1 through 9, in any order but exactly once.

  • Each column must contain the numbers 1 through 9 as well.

  • Each 3x3 subgrid must contain the numbers 1 through 9.

So whenever you enter a number on the grid, verify that number does not already appear in that row, that column, or that 3x3 subgrid.

Click the "5" tile to enter it on the grid

To enter a number on the grid in this Sudoku free online game, first click the location in the grid where you want the number to be set. Then click the appropriate number from the number list shown outside the grid.

For instance, to enter the number "5" on the sudoku board, first click the location where you want to 5 to be entered. Next click the "5" tile that you see along the outside the the board. (See the screen image at left.)

NUMBER HIGHLIGHT FEATURE. To quickly determine where all of a certain number are located on the grid, simply click that number on the board. This highlights all instances of that number.

For example, to see where all the 4's are (that have been entered so far), click one of the 4's on the grid. The rest will display a green background.

The highlight feature in this Sudoku free online game is very useful, because it allows you to rapidly determine whether a particular number already exists in the row, column, or subgrid you are trying to complete.

Sudoku Note-Taking Mode

A really cool feature of this Sudoku free online game is Note-Taking mode.

"Pencil in" notes on the Sudoku grid

Especially at higher difficulty levels, you'll often be able to narrow down the correct entry for a particular location in the sudoku grid to two or three possible numbers. But you won't, at first, be able to say exactly which is correct until more numbers are filled into the grid later.

The note-taking feature allows you to "pencil in" your guesses so you don't forget them. That way you can proceed with your sudoku strategy, later removing your notes and filling in the correct numbers as they become clear.

To enter a numerical note in a specific location in the sudoku grid, first click the square where you want the note to appear. This highlights the square.

Next click the pencil icon, which is displayed on the side of the Sudoku free online game board. This puts you in note-taking mode.

You'll know you are in note-taking mode when you see that the borders around the number selection squares have disappeared. Then click one or more numbers from the list outside the grid that you want to add in the note.

You can pencil in up to all nine numbers, although most of the time you'll want to limit a particular sudoku note to maybe two or three numbers at most. More than that tends to clutter the sudoku grid and create confusion.

For example, suppose I've narrowed down the possible correct entries down to "3" or "7". I can use note-taking mode to enter both 3 and 7 in that square temporarily. The noted numbers display in a small font to distinguish them from permanent entries.

To exit note-taking mode, click the pencil icon again. The borders around the number selections reappear.

Want free sudoku printable pages? Go here.

Sudoku Online Free - Game Options

This sudoku free online game includes a few configurable options, accessible from the Options screen, as follows:

  • Board Animations. I think the sudoku number animations are pretty cool, and they are active by default. Each time you correctly place a number on the sudoku grid, the numbers in that row or column twirl around.

    But if you don't want to see them for some reason, you can disable the animations by clicking the OFF button under the Board Animations heading.

  • sudoku instructions
    Sudoku Instructions screen
  • Show Instructions. Once you understand how to play this sudoku game, you might want to turn this feature off.

    A brief one-screen sudoku game features list displays automatically whenever you start a new round of sudoku. You can easily close screen, but it's a little annoying if you really don't need it.

    You can disable the sudoku instructions so they don't show anymore by clicking the OFF button under the Show Instructions heading.

  • Allow Errors. This option requires a little more thought. When playing sudoku on paper, of course any errors you make remain undetected until you finally figure out that a row, column, or 3 by 3 square has duplicate numbers.

    In this online sudoku game, you can cheat a little and make the game easier by not allowing errors. Clicking the OFF button under the Allow Errors heading prevents you from entering an incorrect number in the sudoku grid.

    You don't get off scott free with this feature, though. Even though you won't be able to place an incorrect number, attempting to do so gives you a time penalty.

TIMER. The elapsed time since you began solving the sudoku puzzle displays at the side of the grid automatically.

You can pause the game anytime by clicking the Pause icon (the two vertical lines icon) above the sudoku board.

MUTE. To turn off the sound effects in this Sudoku free online game, simply click the speaker icon in the upper right corner of the game. To re-enable the sound effects, click the speaker icon again.

I really enjoy solving sudoku puzzles, both on paper and online sudoku games. I'm not fantastically good at sudoku, but I do love the challenge of solving number puzzles.

Sudoku trains numerical reasoning skills and concentration. That's what makes it a great brain game.

Play sudoku often to keep your brain sharp!

Kind regards,
Douglas Jobes

Published: 02/07/2015
Last Updated: 06/11/2020

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