How to Play — Gridmark

Gridmark is a calm, free sudoku you play in your browser — no account, no app, nothing to install. Fill the 9×9 grid so every row, column, and 3×3 box contains the digits 1 to 9 exactly once.

The rules

A sudoku grid is 81 cells arranged as nine rows, nine columns, and nine 3×3 boxes. Each row, each column, and each box must contain the digits 1 through 9 exactly once — no repeats, no omissions. A handful of cells are already filled when you start (the givens); your job is to complete the rest using logic alone. There is always exactly one correct solution, and every puzzle here is generated to guarantee that.

How to play

Tap an empty cell to select it, then tap a digit on the number pad (or press the number key on a keyboard). The digit settles into the cell and the timer starts on your first move. The selected cell highlights, and the cells in its row, column, and box dim so you can read the neighborhood at a glance.

Unsure? Turn on Notes to pencil small candidate digits into a cell instead of committing one. Hint reveals one correct digit, and Check flags any digit that is legal but wrong without telling you the answer. When the last correct digit lands, the timer stops and your result appears.

Tips

• Start with the boxes, rows, or columns that already have the most givens — they offer the fewest possibilities.
• Scan for hidden singles first: a digit that can go in only one cell of a unit, even if other candidates clutter that cell.
• Use notes sparingly. Two or three candidates per cell beats a wall of pencil marks you have to read through.
• If you are stuck, switch between scanning rows, columns, and boxes — the same elimination looks different from each angle.
• Resist guessing. A Gridmark puzzle never requires it on Easy or Medium; Hard leans on box-line logic, and even Expert asks only for a forcing chain — a deduction, not a coin flip — at the very end.
• Play the daily puzzle to build your streak — a one-a-day habit beats a long binge for getting faster.

FAQ

Is Gridmark free? Yes. It is ad-supported, with no account and no payment to play.

Do I need an account? No. Your best times and streak are saved locally in your browser, never uploaded.

What do the difficulty levels mean? They describe the hardest technique a puzzle requires — Easy uses only singles, Medium adds pairs, Hard reaches box-line reduction and triples, and Expert always demands a fish (X-wing or swordfish) or a forcing chain. See the Techniques page for the full ladder.

Is every puzzle unique? Yes. Our generator proves each one has exactly one solution before you ever see it.

Does the daily puzzle change? Yes — it is generated from today’s date, so everyone gets the same puzzle on the same day.