About Sudoku Online

Sudoku Online is a free place to play Sudoku in your browser. You open the page and a puzzle is waiting. No account, no app, no download.

Why I made it

Hi, I'm David. When I was growing up, my mom was always playing the games that came with Microsoft Windows. Solitaire, Minesweeper, FreeCell, a quick round in between other things. What stuck with me is how simple they were. You clicked the icon and you were playing. Nothing to sign up for, nothing to install, nothing getting in the way.

Most free game sites today are not like that. The game is small, the adverts are big, and you wait for things to load. I wanted to build the opposite: a site where the board fills the screen, the puzzle is ready the moment the page opens, and it works as well on a phone as on a computer.

Sudoku Online is one of a small group of free game sites I run with that idea in mind. Sudoku is a good fit for it. It needs nothing but a grid and a bit of quiet, and a good puzzle can be solved with reasoning alone.

Who runs the site

Sudoku Online is run by Lunar Interactive Arts Ltd, a company registered in England and Wales. We also make mobile games.

How the puzzles are made

Every puzzle is made in your browser when you ask for it. The program first builds a complete, valid grid, then removes numbers one at a time. After each removal it runs a solver to check that the puzzle still has exactly one answer. If taking a number away would allow a second answer, that number stays. The givens are removed in mirrored pairs where possible, which is where the balanced look of the starting grid comes from.

The level you choose sets how many numbers are left at the start, from about 42 on Easy down to 22 on Extreme. You can read more in why every puzzle here has exactly one answer.

Why it is free

The site may show a small number of adverts, kept away from the board so they do not get in the way of play. That pays for hosting and for new puzzles and games. Your progress and settings are saved in your own browser, not on our servers. The privacy policy has the details.

Get in touch

Found a bug, have an idea, or want to tell us about a puzzle that drove you mad? Write to support@sudoko-online.com or use the contact page.