About NineByNine

NineByNine is a free sudoku site. Every day there is a new puzzle in four levels, the same for everyone; you can also play unlimited puzzles, print puzzles with answer keys, and paste any puzzle into a solver that explains each step in plain words.

How the puzzles are made

• Every puzzle comes from our own generator. None are copied from books, newspapers or other websites.
• The bank holds 20,368 puzzles. Each was checked by a computer solver to have exactly one solution, then graded by a second solver that works the way a person does and records the hardest technique needed.
• No puzzle needs guessing or trial and error. If you know the techniques for a level, there is always a logical next step.
• The strategy guides use real positions from the same bank, and their practice puzzles were chosen because they require the technique being taught.

How the site works

• There are no accounts. Saved games, settings, stats and streaks stay in your browser.
• Puzzles are generated and checked ahead of time; your browser downloads small puzzle files only when they are needed. Solutions are downloaded only when you check your work or reveal the answer.
• The site uses Google Tag Manager and Google Analytics to count visits (see the privacy policy).

Who runs this site

NineByNine is operated by [to be provided] (owner / legal entity), [to be provided] (country). “NineByNine” is a working name.

“Sudoku” is a registered trademark of Nikoli Co., Ltd. in Japan. NineByNine is not affiliated with Nikoli.

Advertising

Space is reserved above and below the puzzle on some pages for advertising in the future. Ads will never be placed inside or beside the number pad, will never cover the board, and there will be no pop-up ads during a game.

Corrections

If you find a mistake in a guide or a puzzle, please tell us via the contact page and include the puzzle code.