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 the techniques needed to solve it. 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.