Sudoku

How to Play Sudoku

Sudoku is a logic puzzle on a 9x9 grid split into nine 3x3 boxes. Some cells arrive pre-filled as givens; your job is to complete the grid so every row, every column, and every 3x3 box contains each digit from 1 to 9 exactly once. No math is involved - only pure deduction, and every puzzle generated here has exactly one solution.

Click a cell (or move with the arrow keys) and type a digit or tap the number pad. The board checks your work live: a wrong entry turns red and counts as a mistake, and three mistakes end the run - though you can keep playing casually. Toggle pencil mode to jot small candidate digits in a cell while you reason, and watch the highlighting: selecting a cell lights up its row, column, box, and every matching digit on the board. Beat the clock across four difficulties, from a gentle Easy to a brutal Expert with barely two dozen clues.

Strategy Tips

• Start with the most crowded digits - pick the number that already appears six or seven times on the board and chase its remaining placements. Rows and boxes it can't enter narrow the options fast.
• Scan boxes in bands of three - if a digit sits in two of three horizontally adjacent boxes, its position in the third box is confined to one row. This "cross-hatching" solves most Easy and Medium cells without any notes.
• Hunt naked singles after every entry - each digit you place changes what its 20 peer cells can hold. Re-check those cells immediately; chains of forced entries often cascade from a single placement.
• Use pencil marks for pairs, not everything - noting every candidate buries the signal. Mark cells that are down to two or three options; when two cells in a unit share the exact same pair, that pair is eliminated everywhere else in the unit.
• On Expert, look for pointing candidates - when all of a box's candidates for a digit fall in one row or column, that digit is banned from the rest of that line. It's the key that unlocks most low-clue puzzles.