How do you play Sudoku?

Fill the 9x9 grid so every row, every column, and each of the nine 3x3 sub-grids contains the digits 1 through 9. No number may repeat in the same row, column, or 3x3 box.

What do the difficulty tiers mean?

GameZipper Sudoku has six tiers: Beginner (50+ givens, 2 min target), Easy (40-49), Medium (32-39), Hard (26-31), Expert (22-25), and Master (17-21). Fewer starting numbers means a harder puzzle.

How does the 3-star rating work?

Three stars: solve under the target time. Two stars: under 1.5x target. One star: under 2x target. If you finish after 2x the target you still complete the level, but get no stars.

What is the daily puzzle?

A fresh, deterministic puzzle is generated from today's date. Everyone playing on the same calendar day sees the same board, so you can race friends for the best time.

What does pencil mode do?

Pencil mode lets you mark candidate numbers in empty cells as small grey digits. Tap a number with pencil mode on to toggle a candidate; tap a number with pencil mode off to place the real value.

Can I undo a wrong number?

Yes. Every move is saved to a 100-step history. Use the Undo button or the Z key to step backwards. Redo with the Redo button or Y key.

A hint finds the empty cell with the fewest legal candidates and fills in the correct answer. It also costs you one star from the rating for that level.

Does progress save automatically?

Yes. Level completion, star ratings, best times, and settings are stored in your browser's localStorage. Clearing browser data will reset progress.

Can I play on my phone?

Yes. The board uses pointer events so it works with touch, mouse, and stylus. Tap a cell, tap a number. The on-screen numpad is sized for thumbs.

Is the Sudoku generator fair?

Every level is verified to have exactly one solution before it ships. The generator removes cells one at a time and aborts any removal that would create a second valid answer.

Sudoku Online Free — 30 Levels, 6 Difficulty Tiers, Daily Puzzle

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