Sudoku

Sudoku is a number-placement puzzle with nine rows, nine columns and nine smaller boxes. Every row, column and 3 × 3 box must contain the digits 1 to 9 exactly once. You do not need arithmetic: use the placement rules to identify missing positions. The darker numbers supplied at the start are fixed clues and cannot be changed.

This TOFTI edition generates a valid completed grid, then removes some digits. After each removal, it checks that the puzzle still has exactly one solution. Around 39 starting clues remain, though a board may retain more to preserve uniqueness. That count is not a promise of a specific difficulty level; different arrangements can require different deductions.

Selecting a cell highlights its row and column. A repeated digit in its row, column or box is marked red. A digit that is not red is not necessarily correct: a wrong choice may obey the local rules for now. Check compares your current entries with the solution. Hint places one correct digit and increases the hint counter.

Start with a nearly complete row or box. List the missing digits and compare where each one could go. There is no time limit, so you can work from certain placements rather than rushing into guesses. The code and interface were created for TOFTI without advertising, an outside game portal or a required account. Refreshing the page does not preserve the current puzzle.

How to play

Select an empty cell, then choose an on-screen digit or press a number key from 1 to 9. Erase, Delete, Backspace or 0 clears the selected cell. Fixed starting clues cannot be erased.

Use the arrow keys to move between cells. Check highlights incorrect entries. Hint fills the selected cell correctly; if it is already correct, another missing or incorrect cell is chosen.

Completing all 81 cells correctly shows the solved message. New game opens a different puzzle. Before using a hint, check which digits already appear in the selected cell's row, column and box.