Sudoku: game rules

🎯 Goal: Fill the grid so that every row, every column and each of the nine boxes holds each digit from 1 to 9 exactly once. Every puzzle has exactly one solution.

✏️ Playing: Pick a cell, then tap a digit or press the keys 1–9. With "Notes" (key N) you enter small candidates; they disappear by themselves when the digit is set nearby. "Undo" takes steps back, "Erase" (Backspace) clears the cell. The arrow keys walk the board. Solo you can pause: the clock stops and the board is covered.

💡 Help: Solo, the host can switch on "Mark mistakes at once": a wrong digit then gets a red frame. A hint fills the chosen empty cell correctly. If the board is full but not right, "Check" shows the wrong cells.

🏁 Race: With several players everyone gets the same puzzle. You only see the others' progress, never their digits. The board is only checked when you hand in a full one: wrong cells are marked and cost 30 seconds, and so does a hint. The fastest time including penalties wins; the race runs until everyone has finished or given up. Once somebody has solved it, the others only get the set extra time (5 minutes by default, can be switched off); after that the number of correctly filled cells decides the places.

🏆 Best time: For each level (easy, medium, hard) your account keeps your fastest solve. It only counts without help: no hint, no mistake marking, no submission with mistakes.