OK Sudoku

Play Sudoku online for free and without ads

OK Sudoku is a browser-based web sudoku puzzle game created for the love of it. Play it for free in your browser on phone or computer. No downloads, no sign-up, no ads. Please excuse the sales pitch and the waffling - gotta get some keywords onto the page so we'll show up in search results.

There are hundreds of boards. Each board is graded as one of easy, medium, hard, or advanced, depending the sophistication of the techniques needed to solve it.

Press New Board to try a different board.

Press Check to see if you've made any mistakes. Correct entries will be highlighted green. Incorrect entries will be highlighted red and crossed out.

Press a cell, and use the on-screen keyboard to enter a value, or use your device's physical keyboard.

What is Sudoku?

Sudoku is a popular logic-based puzzle game played on a 9x9 grid. Despite all the numbers, it's not about math. The numbers could be subsituted for letters or emojis and game would still work the same way. The goal is to fill each row, column, and 3x3 box with the numbers 1 through 9, without repeating any numbers in the same row, column, or box.

It's a simple concept, but it can be quite tricky and require the use of some logical thinking.

Tips for solving Sudoku puzzles

Start with the obvious numbers

Start by scanning the entire grid, looking for:

Rows, columns, or boxes that already contain many numbers - these will be easier to complete.
Number that already appear frequently on the board. Try to find where the rest of that number could go.

Use "pencil marks"

For all the but the easy puzzles (and maybe for the easy ones too), you'll need to keep track of possible numbers in empty cells.

Use the ✎ button to toggle on pencil marks. Pressing a number after turning on pencil marks will lightly mark the selected cell with that number.
Use pencil marks to annotate which values a cell can be
As you find numbers that go in cells, see if any of the pencil marks you previously added can be removed. This can narrow down the of possible values that cells can be, until it can only be one number.

Look for "naked singles" and "hidden singles"

A naked single is a cell that only has possible number left based on the other numbers in its row, column, or box. It must be that number. Every other number you would put there would cause a dupliate in a row, column or box.

A hidden single is a number that can only go in one spot in a row, column, or box - even if that spot has other candidates. That number can't go in any other spot because it would cause a duplicate.

Don't guess

Sudoku is a logic puzzle, not a guessing game. If you guess and you get it wrong, you'll end up with a mess that's hard to get out of. Maybe you guess right - but that's not very fun - and you'd have to keep guessing right.

Keep practising

Play easy puzzles or puzzles that are just a little bit difficult for you. That way you have fun as you get better, instead of getting frustrated. Master easy and medium, before moving on to hard sudoku.

Well, that's the end of the waffling on this page. The things one must do to appease the search engine gods!

By Joel Plane. Suggestions? Bugs? Contact me