Sudoku

Yes, Sudoku is completely free. Free Play offers unlimited puzzles at every difficulty level without an account. Creating a free account unlocks Competitive mode where you earn points and climb the monthly leaderboard.

OfficeGames.io offers four difficulty levels: Easy, Medium, Hard, and Expert. Easy puzzles have more pre-filled cells and can be solved with basic techniques. Expert puzzles require advanced strategies like X-Wing, Swordfish, and hidden pairs. The daily Competitive puzzle rotates difficulty throughout the week.

Yes. The pencil mark feature lets you annotate cells with possible candidate numbers. Toggle pencil mode with the pencil icon or press P on your keyboard. Pencil marks are automatically cleared when you place a final number in that cell or when the number is eliminated by a placement in the same row, column, or box.

The timer starts when you fill your first cell and is visible in the game header. It pauses automatically when you switch tabs or minimize the browser. In Competitive mode, faster completion times earn bonus points and serve as the tiebreaker when players have equal monthly point totals.

Easy gives you the most starting clues and can be finished with scanning alone. Medium is the balanced option and the one most players settle on. Hard and Expert strip out clues until you need real techniques — hidden singles and candidate pairs rather than just spotting the obvious cell. All four are available in Free Play with no account, so you can move up whenever you want to.