Free Online Sudoku

Fill the 9×9 grid so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. Start where the grid is most crowded — a row, column, or box that already has six or seven numbers — and use elimination to work out what fits in each empty cell. MoonDoku highlights related cells as you play.

There are only three rules.

• Each row must contain the numbers 1 to 9, with no repeats.
• Each column must contain the numbers 1 to 9, with no repeats.
• Each 3×3 box must contain the numbers 1 to 9, with no repeats.

Every MoonDoku puzzle has exactly one solution, and you can always reach it with logic alone — no guessing required.

Yes — you can play Sudoku online for free every day, right in your browser, with no download or sign-up required. Everyone gets the daily Nightly challenge — one shared puzzle a day — and a free account saves your scores, streaks, and achievements across devices. A one-time purchase unlocks the full game on moondoku.com — unlimited puzzles across Easy, Medium, Hard, and Expert.

Every puzzle is graded by how much work it takes to solve, not by how many digits are missing. Easy puzzles are perfect for learning the basics, Medium suits a relaxed daily solve, Hard demands deeper deduction, and Expert brings the toughest grids we generate.

Re-scan the rows, columns, and boxes that cross your empty cell — there is always a next logical step, even when it hides well. If you are still stuck, use a hint to reveal a correct number — sometimes one cell is all it takes to get the logic flowing again.

A daily puzzle is a small, satisfying workout for your brain — it sharpens concentration, logical reasoning, and working memory, and many players find it a calming break from a busy day. MoonDoku tracks your daily streak and achievements, so it is easy to make the habit stick.

Yes — MoonDoku is also an app on Steam for Windows, macOS, and Linux (paid once, everything included) and on the App Store for iPhone and iPad (free to download; a one-time purchase opens the full game), with thousands of puzzles that play offline and the same Nightly as everyone else. See where to play. Each edition is bought where it lives, and your free account travels everywhere.