A
Standard Rules Apply
Classic rules still apply: 1–9 appears once in every row, column, and 3×3 block.
How to Solve Sudoku
Learn how to solve Sudoku step by step using row, column, and 3×3 box rules, then practice the logic on a free online puzzle.
Classic Sudoku
1
The Grid Structure
The board is a 9×9 grid divided into nine 3×3 blocks (regions). Every empty cell belongs to exactly one row, one column, and one block.
2
The Goal
Fill every empty cell with digits 1–9. You start from a partially completed puzzle with one unique solution—no guessing required when you use sound logic.
3
The Golden Rule
Digits 1–9 cannot repeat in any row, column, or 3×3 block — each must appear exactly once. If a digit already exists in a unit, it cannot appear again there.
Killer Sudoku
Killer Sudoku adds cage sums to classic Sudoku rules. The steps below summarize the extra constraints; open the full Killer guide for examples, cage combinations, and Hell Mode practice.
B
The Cages
Cells grouped by dotted outlines are “cages”.
C
The Sum Constraint
Digits in a cage must sum to the small number shown in its top-left corner.
D
No Repeating Digits in Cages
Digits cannot repeat within a single cage, even if the cage spans multiple blocks.
Beginner solving tips
Scan for singles first
Look for a digit that can only fit in one cell of a row, column, or box. These “naked singles” and “hidden singles” clear the easiest placements without notes.
Use pencil marks sparingly
Candidate notes help on medium and harder puzzles, but marking every empty cell too early creates noise. Prefer scanning first, then note only contested cells.
Never guess
A well-formed Sudoku puzzle has a unique solution reachable by logic. If you feel stuck, revisit rows and boxes you have not scanned since the last placement.
Sudoku FAQ
How do you play Sudoku?
Fill a 9×9 grid so every row, column, and 3×3 box contains each digit from 1 to 9 exactly once. Use the given clues and eliminate impossibilities until only one digit remains for each empty cell.
What is the difference between easy and hard Sudoku?
Easy Sudoku puzzles start with more given digits and leave fewer cells to solve. Hard puzzles have fewer clues and usually require techniques such as hidden singles, pairs, and longer elimination chains.
Do I need to download an app to play on Sudoku Hot?
No. Sudoku Hot runs in your browser on phone, tablet, or desktop. Progress and preferences can stay on your device without creating an account.
What are pencil marks (notes)?
Notes are small candidate digits you write in a cell while you still have more than one possibility. They help track options until logic proves which digit belongs there.
Is guessing allowed?
You can enter any digit, but high-quality Sudoku puzzles are designed to be solved by pure logic. Guessing often creates contradictions later and trains weaker habits.
How is Killer Sudoku different?
Killer Sudoku keeps classic row, column, and box rules, then adds cages with sum clues. Digits inside a cage must add to the clue and cannot repeat inside that cage.