What is Sudoku?
Sudoku is a logic-based number puzzle played on a 9×9 grid. The grid is divided into nine 3×3 boxes. Your goal is to fill every empty cell with a number from 1 to 9 — following three simple rules.
The word "Sudoku" comes from Japanese and means something like "single number". Although the game uses numbers, no math is required — only logical thinking.
The Three Rules
Rows
Every row must contain the digits 1–9, each appearing exactly once.
Columns
Every column must contain the digits 1–9, each appearing exactly once.
3×3 Boxes
Every 3×3 box must contain the digits 1–9, each appearing exactly once.
Step-by-Step: Solving Your First Puzzle
- Scan for easy cells. Find rows, columns, or boxes that already have 7 or 8 numbers. The missing digit is the only option.
- Use elimination. For each empty cell, eliminate numbers already present in the same row, column, and box. If only one number is left, place it.
- Look for hidden singles. In a group (row, column, or box), find a number that can only fit in one cell. Place it there.
- Use pencil marks (notes). In harder puzzles, write small candidate numbers in empty cells. Cross them off as you make placements.
- Repeat. Each number you place reveals more information. Keep scanning until the board is complete.
Basic Strategies
- Cross-Hatching Pick a digit (say, 5). Draw imaginary lines through every row and column that already contains a 5. The cells where no lines cross — inside each 3×3 box — are your candidates. Often only one cell remains.
- Naked Singles An empty cell where elimination leaves only one possible candidate. This is the simplest and most common move in easy and medium puzzles.
- Naked Pairs Two cells in the same group that both contain only the same two candidates. These two numbers are "locked" in those two cells — you can safely remove them from all other cells in the group.
Tips for Beginners
- Start with the Easy difficulty to learn the basics.
- Never guess — every Sudoku puzzle has a unique logical solution.
- Use the notes feature in SUDOQIO to pencil in candidates (press N or tap the pencil icon).
- The app auto-clears notes when you place a correct digit — keeping your board clean.
- Practice the daily puzzle every day to build speed and pattern recognition.
Difficulty Levels at SUDOQIO
Game Features
6 Visual Themes
Choose from 6 unique visual themes — Cyberpunk, Neon, Dark, Matrix, Classic White, and Warm Paper. Your theme is saved automatically and applies across all game modes.
Smart Notes
Press N (or tap the pencil icon) to switch to note mode. Type candidate numbers into empty cells as small hints. Notes auto-clear when you place a correct digit — keeping your board clean.
Cross-Device Sync
Create a free account to sync your stats, streak, XP and progress across all your devices. No password needed — sign in with a magic link sent to your email.
Conflict Highlighting
Duplicate numbers are highlighted in red instantly. If you place the same digit twice in a row, column, or box, both cells turn red — so you always know where the conflict is without needing to check manually.
Auto-Notes
Tap the Auto-Notes button in the toolbar to fill every empty cell with all valid candidate numbers at once. A great head-start for harder puzzles. Note: using Auto-Notes counts as 3 hints and reduces your score accordingly.
Points & Scoring
Base Score
Determined by difficulty: Easy (1000), Medium (2500), Hard (5000), Expert (10000).
Time Bonus
Earn +5 points for every second you finish under the target time (Easy: 3m, Medium: 8m, Hard: 15m, Expert: 30m).
Combo Bonus
Solve cells quickly and correctly to build a combo. You get +50 points for each combo level.
Hint Penalty
Using a hint permanently reduces your final score by 10%.
Mistake Penalty
Each mistake reduces your final score by 5%. You can make at most 2 mistakes — the third ends the game.
🔥 Daily Streak
What is a Streak?
Your streak counts how many days in a row you have solved the daily puzzle. It is shown in the game header and on the home screen. Your all-time best streak is tracked separately.
How to Keep It Alive
Solve the daily puzzle before midnight (your local time) each day. Every day you solve it, your streak grows by one. Log in to sync your streak across devices — otherwise it is stored locally in your browser.
When Does It Reset?
If you miss a day, your streak resets to 1 the next time you solve the daily puzzle. Your best streak is never lost — it stays as your personal record.
Sync Across Devices
Without an account your streak is saved only in this browser. Log in for free to back it up to the cloud and keep it when you switch devices.
🏆 XP & Player Ranks
How to Earn XP
Every solved puzzle earns you Experience Points (XP). The base amount depends on difficulty: Easy ≈ 100 XP, Medium ≈ 150 XP, Hard ≈ 250 XP, Expert ≈ 400 XP. Solving quickly adds a speed bonus (up to +150 XP), while each hint costs −20 XP. Completing the Daily Puzzle gives an additional +250 XP bonus on top. XP carries over — you always make progress, no matter the result.
The 9 Ranks
There are 9 ranks to climb, from Novice to Zen Master. Each rank unlocks at a specific level — see the table below.
Ready to practice?