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Free online Sudoku

Free online Sudoku is a classic logic puzzle game where players fill a 9×9 grid using numbers 1–9 without repeating them in any row, column, or box. At Solitrd, you can play free online Sudoku instantly, choose your preferred difficulty level, and enjoy brain-training puzzles anytime, anywhere—no download required.

How to Play Sudoku ?

  1. The Grid: Standard Sudoku uses a 9×9 grid divided into nine 3×3 subgrids
  2. The Objective: Fill every row, column, and 3×3 box with numbers 1-9
  3. The Rule: No number can repeat in any row, column, or 3×3 box
  4. Starting Point: Puzzles begin with some cells pre-filled as clues

Sudoku Strategy : From Beginner to Advanced

Beginner (Easy Puzzles)

  1. Scan: Check rows/columns for missing numbers
  2. Single Candidate: Only one number fits in a cell
  3. Single Position: A number has only one spot in a row/column/box

Intermediate (Medium Puzzles)

  1. Pencil Marks: Note possible numbers in cells
  2. Pairs/Triples: If 2–3 cells in a unit share the same 2–3 numbers, eliminate those from other cells
  3. Pointing Pairs: Candidates in a box align in one row/column → remove from rest of that row/column

Advanced (Hard Puzzles)

  1. X-Wing: Two rows where a number appears in only two same columns → eliminate from those columns elsewhere
  2. XY-Wing: Three cells with number patterns (pivot and two wings) → eliminate specific candidate
  3. Skyscraper / Two-String Kite: Chain patterns using two rows and two columns

Pro Tips:

  • Start with scanning → use pencil marks when stuck
  • Never guess — every move should have logical proof
  • Practice one technique at a time
  • Take breaks; fresh eyes spot patterns

Quick Process:

Scan → Fill singles → Add pencil marks → Find pairs/triples → Try X-Wing/XY-Wing → Repeat

Advanced Sudoku Techniques and Tips

  1. Notation Systems: Master full notation (pencil marks) for hard puzzles
  2. Pattern Recognition: Train your eye to spot common advanced patterns
  3. Candidate Elimination: Systematically remove possibilities rather than guessing
  4. Time Management: Balance speed with accuracy in tournament settings
  5. Backtracking Strategy: When stuck, make hypothetical placements and track contradictions

Sudoku Tournaments and Competition

  • World Sudoku Championship: Annual international competition
  • Online Tournaments: Regular events on platforms like Logic Masters and Sudoku Cup
  • National Competitions: Most countries have national championships
  • Local Tournaments: Check libraries, game stores, and puzzle conventions

Tournament Preparation

  • Practice with time constraints
  • Master your notation system
  • Learn to recognize patterns quickly
  • Develop mental stamina for multi-hour competitions

Sudoku Solver Step-by-Step Approach

  1. Re-scan the entire grid for obvious placements
  2. Update all pencil marks completely
  3. Apply basic strategies (singles, pairs, triples)
  4. Try intermediate techniques (pointing pairs, box/line reduction)
  5. Apply one advanced technique at a time
  6. If still stuck, take a break - fresh eyes often spot what you missed
  7. As last resort, make a hypothetical placement and follow the logic chain

Printable Resources

  • Difficulty Graded Puzzles: Easy to "evil" levels
  • Specialty Puzzles: Killer, Samurai, Diagonal, and Irregular Sudoku
  • Solution Templates: For tracking your progress
  • Strategy Cheat Sheets: Quick-reference guides for techniques

    Sudoku Online : FAQ

  • What is Sudoku?

    Sudoku is a logic-based number placement puzzle where players fill a 9×9 grid so that each row, column, and 3×3 subgrid contains all digits from 1 to 9 without repetition. No math skills are needed—just pure logical reasoning.

  • What are the basic Sudoku rules?

    • Row Rule: Each horizontal row must contain numbers 1–9 without repetition
    • Column Rule: Each vertical column must contain numbers 1–9 without repetition
    • Box Rule: Each 3×3 subgrid must contain numbers 1–9 without repetition

  • What is Killer Sudoku?

    Killer Sudoku adds “cages” (dotted outlines) with sum targets. Players must:

    • Follow standard Sudoku rules
    • Ensure numbers in cages sum to the given total
    • Avoid repeating numbers within cages

  • What are the benefits of playing Sudoku regularly?

    Cognitive advantages:

    • Improves concentration and focus
    • Enhances logical thinking
    • Develops pattern recognition
    • May support memory retention
    • Provides stress relief through focused activity

  • How do Sudoku tournaments work?

    Typical tournament structure:

    • Multiple rounds of increasing difficulty
    • Timed solving (30–120 minutes per round)
    • Scoring based on accuracy and speed
    • Variants often included (Killer, Diagonal, etc.)
    • World Sudoku Championship held annually

  • What are pencil marks and why are they important in Sudoku?

    Pencil marks (also called “notes” or “candidates”) are small numbers written in empty cells to track possible values. They're essential for medium to hard puzzles and help you spot patterns like pairs, triples, and advanced solving techniques.

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