About Sudoku Online
Sudoku Online is a free Sudoku site run by Sudoku Online Editorial Team. It offers classic 9×9 Sudoku at five levels and ten other boards, hints that name the technique you need, and a library of lessons, guides and history pages. Every puzzle has exactly one solution and is graded by the techniques it requires.
This page explains what the site is, how its puzzles and pages are made, and how to reach us.
What is Sudoku Online?
The site has two parts. The first is a game: a Sudoku board that runs in your browser on a phone, tablet or computer, with notes, undo, hints, a daily puzzle and a no-help expert mode. The games hub lists every board. The second part is teaching material: twelve technique lessons in the techniques hub, ten tutorials in the guides hub, and four pages in the history hub about where Sudoku came from and the mathematics behind it.
You do not need an account to play, and there is nothing to sign up for.
Who runs it?
The site is operated by Sudoku Online Editorial Team. You can reach us at [email protected] or through the contact page.
How are the puzzles made?
Puzzles are generated by the site’s own program and not copied from other sites, books or apps. The program builds a grid, removes clues while the puzzle stays uniquely solvable, and then grades the result by the techniques a solver needs. A check that runs before every release re-solves every stored puzzle and confirms it has exactly one solution and matches its level. The details are in how puzzles are generated and verified unique and how difficulty is graded. The levels are this site’s own grading and not an industry standard, and the guides say so.
How is the content written and checked?
Numbers on the site come from the site’s own data and scripts, walkthroughs use real stored puzzles, and history pages list their sources and say where those sources disagree. The editorial policy describes the process, including how content is drafted and reviewed, and how corrections are handled.
How is the site paid for?
Playing is free. The site is intended to be supported by display advertising, shown through Google AdSense once an account is approved. Advertising does not change how puzzles are chosen, how hints work or how difficulty is graded, and the site does not sell your personal information. How advertising and measurement interact with your privacy choices is explained in the privacy policy and the cookie policy.
What should you do if something is wrong?
If you find a wrong puzzle, an error in a lesson, an accessibility problem or a bug, please tell us through the contact page. Say which board and level you were playing, or which page you were reading, and what you expected to see. The FAQ answers common questions, and the glossary explains the terms used on the site.