Welcome to SudokuEvil.io, your ultimate destination for free Sudoku online. We offer thousands of Sudoku puzzles across 6 difficulty levels: easy, medium, hard, evil, expert, and insane. Every day we generate fresh free Sudoku games so you never run out of challenges. Our Sudoku game works perfectly on mobile, tablet, and desktop with no downloads or registration required.
Sudoku games aren't math despite using numbers 1-9. Pure logical deduction. Mental exercise that's actually fun. Fill every row, column, and 3x3 box with unique digits.
Simple rules. Brutal execution.
Most players get hooked after their first puzzle game. Fair warning: Sudoku Evil will eat entire weekends.
Choose Your Difficulty Level
Easy Sudoku - Perfect for Beginners
Easy Sudoku gives you 35-40 starting numbers. Perfect for beginners who want to learn the fundamentals without frustration. These puzzles solve using basic techniques like scanning and naked singles.
Medium Sudoku - The Next Step
Medium Sudoku removes more clues, requiring you to think several moves ahead and use hidden singles techniques.
Hard Sudoku - For Experienced Players
Hard puzzles demand advanced techniques like pointing pairs and box-line reduction strategies.
Evil Sudoku - The Ultimate Challenge
Evil Sudoku starts with only 17 numbers - the mathematical minimum. Requires advanced techniques like X-Wing, Swordfish, and forcing chains that 99% of players never master.
Expert Sudoku - Masters Only
Expert level puzzles are the ultimate challenge, requiring multiple advanced techniques in combination.
How to Play Sudoku Online
Basic Sudoku Rules
Sudoku games aren't math despite using numbers 1-9. Pure logical deduction. Fill every row, column, and 3x3 box with unique digits. Each puzzle has exactly one solution reachable through logic alone - never guess!
Sudoku Solving Techniques
Start with basic scanning and elimination. Learn naked singles and hidden singles. Advanced players use X-wings, swordfish, and forcing chains. Master the fundamentals before attempting evil Sudoku puzzles.
Available Sudoku Variants
Classic 9x9 Sudoku
Traditional Sudoku puzzles with numbers 1-9 on a 9x9 grid. Master this format first before trying variants. Available at all difficulty levels from easy to evil.
Killer Sudoku
Killer Sudoku adds arithmetic constraints with cage sums. More challenging than classic Sudoku, requiring both logical and mathematical skills. Start with easy Killer Sudoku to learn the rules.
Samurai Sudoku
Five overlapping 9x9 grids form one massive puzzle. Samurai Sudoku demands advanced planning and pattern recognition across multiple interconnected grids. Explore all Sudoku variants or discover the fascinating history of Sudoku.
Why Play Sudoku at SudokuEvil.io?
Sudoku Brain Benefits
Research shows a 15-20% improvement in working memory with regular Sudoku practice. Better concentration, faster pattern recognition, and improved logical reasoning are real benefits, not marketing claims. Learn more about Sudoku brain benefits.
Game Features
Unlimited free puzzles, no ads, no registration required. Works perfectly on phone, tablet, and desktop. Auto-save protects your progress. Daily challenges and multiple difficulty levels keep you engaged.
🎨 Eight Visual Themes
Forest Green for daytime. Dark Mode for evening marathons. Find what works during those 4-hour evil sessions. Visual comfort matters when you're tracking dozens of candidates.
Progress tracking records everything. Solving times, accuracy rates, difficulty preferences. Good for monitoring improvement.
Less good for ego when you're stuck on medium puzzles for weeks.
⚔️ Master Advanced Techniques
Basic scanning and elimination? Kid stuff. Advanced techniques like X-wings and swordfish separate weekend players from serious solvers.
Build foundations first. Master crosshatching and naked singles before attempting forcing chains. Those scary names become second nature.
Skip steps? You'll struggle forever.
🔧 Professional-Grade Engine
Every puzzle guarantees exactly one solution. Fast loading, responsive design, bulletproof auto-save. Use the step-by-step solver when you're completely stuck.
Supports 15+ languages, full accessibility, zero tracking. Play anonymously or track stats.
Your choice entirely.
No ads, no subscriptions, no BS.
🚀 Start Playing Now
Choose your difficulty. New players must start with easy puzzles to learn fundamentals. Advance when you're solving under 20 minutes consistently.
No time pressure. No registration. No subscriptions. Just logical thinking and pattern recognition.
That's what makes Sudoku addictive.
Choose Your Challenge Level
Start easy to build confidence, or jump straight to expert puzzles if you're experienced
❓ Frequently Asked Questions
How long does it take to learn Sudoku?
Basic rules? 5-10 minutes. Getting decent at easy puzzles takes 1-2 weeks. Advanced techniques for expert stuff? Months.
Evil level? Most people never get there.
Do I need math skills for Sudoku?
Zero math required. Despite using numbers 1-9, it's pure logic and pattern recognition. No arithmetic—could use letters instead.
Pure reasoning.
What's the difference between easy and evil difficulty?
Easy gives you 35-40 starting numbers. Evil gives you 17. That's the mathematical minimum. Requires advanced techniques like forcing chains that 99% of people never learn.
Does Sudoku actually improve brain function?
Studies show 15-20% improvement in working memory. Better concentration, faster pattern recognition. Real benefits, not marketing fluff like other brain training apps.
Should I guess when I'm stuck?
Never guess. Ever. Every proper Sudoku has exactly one solution reachable through logic. Guessing means you're missing a technique. Learn it instead.
What techniques should beginners learn first?
Start with scanning and basic elimination. Then naked singles and hidden singles. These four methods solve most easy and medium puzzles. Master these before advancing.
When should I move to harder levels?
When you solve current level under 20 minutes consistently. No getting stuck, no frustration. Speed isn't everything—master fundamentals first or you'll struggle later.
Are there variants beyond standard 9x9?
Killer Sudoku adds arithmetic. 16x16 grids use hexadecimal. Diagonal Sudoku includes main diagonal rules. Master classic 9x9 first—variants build on fundamentals.
Why do some puzzles seem impossible?
You've hit your skill ceiling. Evil-difficulty puzzles require X-wings, swordfish, and forcing chains. Techniques that aren't intuitive without training. Time to level up.
Paper versus digital—which is better?
Digital tracks candidates automatically. Paper strengthens memory. For evil-level stuff, paper wins—easier to draw constraint lines and track complex eliminations. Both have merit.
Your Brain Challenge Awaits
Start training your mind with scientifically-proven puzzles. No registration, no cost, no commitment.