Fill every row, column, and 3x3 box with the digits 1-9. No digit can repeat within a row, column, or box.
Buttons
New — Start a fresh puzzle at the selected difficulty
Check — Highlight all incorrect entries in red
Solve — Reveal the full solution (ends the game)
Hint — Two-step hint: first shows which cell to fill, then reveals the digit with reasoning (Naked Single, Hidden Single, etc.)
Notes (Pencil Marks)
Tap Notes (or press N) to toggle notes mode. While active, tapping a number adds/removes it as a small pencil mark instead of placing a value. Placing a real number auto-clears pencil marks from its row, column, and box.
Highlights
Purple — The cell you selected
Yellow tint — Its row, column, and 3x3 box (what it "sees")
Green tint — Every cell containing the same number
Red — Wrong entries (only shown after Check, or live for errors)
Keyboard shortcuts
1-9 — Place a digit (or add pencil mark if Notes is on)
Backspace / Delete — Erase the cell
↑↓←→ — Move selection
N — Toggle Notes mode
Auto-save
Your progress (board, timer, notes, errors) is saved in your browser. Close the tab and come back to pick up where you left off.