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 — MoonDoku is completely free, right in your browser with no download required. Everyone gets the daily Nightly challenge — one shared puzzle a day — and a free account unlocks 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.