🔢 Sudoku

How to play

A 9 by 9 grid is generated complete and then around fifty cells are emptied, leaving the given numbers in grey. Fill every blank so that each row, each column and each of the nine three by three boxes contains the digits 1 to 9 exactly once. Select a blank cell first, then enter a digit. The puzzle is finished when every cell matches the solution the generator started from.

• Click a cell — select it. Given cells cannot be selected or changed.
• Number keys 1 to 9 — place that digit in the selected cell.
• Numpad buttons — the same nine digits below the grid, plus a cross that clears the cell.
• Delete or Backspace — clear the selected cell.
• Hint button — fills the selected cell with its correct value.
• New Game button — generates a fresh puzzle.

Scoring

There is no score, no timer and no penalty for a wrong entry. The grid checks each digit against the solution as you type it and shows a wrong one in red immediately, so this plays as a guided puzzle rather than a test. Completing the grid replaces the prompt below it with a congratulation message. Hints cost nothing but are not counted either.

Tips

• Start with the row, column or box that has the fewest blanks. One cell with a single possible digit usually unlocks several more.
• Because wrong digits turn red at once, you can test a candidate rather than working it out on paper, then clear it if it is rejected.
• Scan for a digit rather than for a cell. Ask where the 7 can go in this box, not what can go in this cell.
• Save the Hint button for a genuine dead end. It fills the selected cell, so select the cell you are actually stuck on first.

Frequently asked questions