Resources

Guides, strategies, comparisons, and everything sudoku.

Guías de sudoku en español

New to sudoku? Start on the Learn page

The rules, a first full solve, then the 13 techniques in learning order, each with a drill.

Learn sudoku step by step

Technique guides

One guide per technique, each with a worked example from a real puzzle.

Full House in Sudoku: The Last Remaining Cell

The full house (last remaining cell) is the simplest sudoku placement. How to spot it instantly and why it matters for your solve times.

Naked Singles in Sudoku: How to Find Them Fast

What a naked single is, how to spot one without counting to nine, and how it differs from a hidden single. With examples and practice tips.

Hidden Singles: The Most Important Sudoku Technique

Hidden singles place more digits than any other technique in most sudoku puzzles. Learn the rule, a worked example and a fast way to scan for them.

Pointing Pairs and Box-Line Reduction Explained

Two related techniques that eliminate candidates by analyzing how boxes and lines interact. Essential for intermediate solvers.

Claiming in Sudoku: Box-Line Reduction Explained

Claiming, also called box-line reduction, removes candidates from a box. Learn the rule, follow a real example, and see how to spot it while solving.

Naked Pairs in Sudoku: How to Spot & Use Them

Master the naked pairs technique, one of the most useful intermediate sudoku strategies, with clear visual examples.

Hidden Pairs in Sudoku: How to Spot and Use Them

A hidden pair is two digits confined to the same two cells. How to find hidden pairs by counting digits, what to eliminate, and a worked example.

Naked Triples in Sudoku: Explained with Examples

How naked triples work, why no cell needs all three digits, how to find them, and how they relate to naked pairs and quads.

Hidden Triples in Sudoku: How to Find Them

A hidden triple is three digits that fit in only three cells of a group. A worked example and the shortcut that makes them easy to find.

X-Wing Strategy in Sudoku: Visual Guide

The X-Wing pattern is a powerful advanced sudoku technique. This visual guide shows you exactly how to find it and how to use it.

Swordfish Technique: Advanced Sudoku Strategy

The Swordfish extends the X-Wing to three rows and three columns. Learn this expert-level technique with a step-by-step example.

XY-Wing (Y-Wing) in Sudoku: Pivot and Pincers Explained

How the XY-Wing works, why one pincer must hold the shared digit, which cells you can clear, and how to search for the pattern.

Simple Coloring in Sudoku: Conjugate Pairs and Chains

How simple coloring (simple colouring) works: build a two-color chain on one digit and use the color wrap and color trap rules to eliminate candidates.

Skyscraper Sudoku Technique: How to Spot It, With Real Examples

A skyscraper is two strong links on one digit that share a base line. See how to spot it, two verified examples from real puzzles, and how it differs from an X-Wing.

Unique Rectangle in Sudoku: Types 1, 2, 3 and 4 Explained

How unique rectangles use the one-solution rule to remove candidates. Every type from 1 to 4, each with a verified diagram from a real puzzle and a way to spot it.

Snyder Notation: The Fast Pencil Mark Method for Sudoku

Snyder notation marks a digit only when it has two spots left in a box. How it works on a real puzzle, why fast solvers use it, and when to switch to full candidates.

BUG+1 in Sudoku: The Bivalue Universal Grave Explained

When every open cell has two candidates except one cell with three, BUG+1 tells you that cell's answer. How to spot it and check it, shown on a real puzzle.

2-String Kite Sudoku Technique, With a Worked Example

A 2-String Kite joins a row link and a column link through one box to remove a candidate. How to find it, why it works, and a verified example from a real puzzle.

Empty Rectangle in Sudoku: How the Box Pattern Works

An empty rectangle is a box where one digit sits in a cross shape. Paired with a strong link, it removes a candidate. Step-by-step example from a real puzzle.

XYZ-Wing in Sudoku: How It Works and How It Differs From XY-Wing

An XYZ-Wing is a three-candidate pivot with two two-candidate pincers. Learn where its eliminations land, how to find one, and see a verified example.

W-Wing Sudoku Technique: Two Matching Pairs and a Strong Link

A W-Wing uses two identical two-candidate cells joined by a strong link on one of their digits. How to spot it and a worked example from a real puzzle.

Jellyfish in Sudoku: The Four-Row Fish, Explained Simply

A jellyfish is the four-line member of the fish family after X-Wing and Swordfish. How it works, how rare it is, and a real example with seven eliminations.

Finned X-Wing in Sudoku: How the Fin Works (With Diagram)

A finned X-Wing is an X-Wing with one extra candidate, the fin. Learn which cells you can still clear, how to spot the pattern, and see a verified example.

X-Chain in Sudoku: Single-Digit Chains for Beginners

An X-Chain alternates strong and weak links on one digit. If both ends see a cell, that cell loses the digit. A beginner-friendly guide with a real example.

XY-Chain in Sudoku: Linking Two-Candidate Cells Step by Step

An XY-Chain links two-candidate cells so one end must hold the same digit. How to build one, read it, and use it, with a verified five-cell example.

3D Medusa Sudoku Technique: Colouring Across Digits

3D Medusa extends simple colouring to several digits at once. The rules, how to colour a grid, and a real example where one cell holds both colours.

Almost Locked Sets (ALS) in Sudoku: ALS-XZ for Beginners

An almost locked set is N cells with N+1 candidates. How two of them combine in the ALS-XZ rule, how to find them, and a verified example from a real puzzle.

Strategy & Tips

Slide to Select: The Fastest Way to Play Sudoku

How slide-to-pick input works in Sudoku Royale: press a cell, slide into the box of the digit you want, and lift. Why box-sized targets beat a small keypad.

How to Play Sudoku: Complete Beginner's Guide

Learn the rules of sudoku and solve your first puzzle step by step. The only guide beginners need.

15 Sudoku Tips Every Beginner Should Know

Practical tips that will immediately improve your sudoku solving, from scanning techniques to common mistake avoidance.

How to Solve Sudoku Faster: Speed Techniques

Speed-solving techniques that actually work: pattern recognition, scanning order, and habits that cut minutes off every puzzle.

Sudoku Pencil Marks and Notes Explained

What sudoku pencil marks (notes) are, when to start writing them, Snyder vs full notation, and how notes work in a phone app, including auto-removal and auto-fill.

Sudoku Difficulty Levels Explained: Easy to Evil

What makes a sudoku puzzle easy, medium, hard, or evil? A breakdown of difficulty ratings and the techniques each level requires.

Advanced Sudoku Strategies for Expert Players

XY-Wing, coloring, unique rectangles, and more. The advanced techniques that separate expert solvers from the rest.

Sudoku Speed Solving: Techniques Used by the Fastest

How the fastest sudoku solvers in the world approach a puzzle: their scanning patterns, decision habits, and practice methods.

How to Solve Sudoku: A Step-by-Step Method

How to solve any sudoku, step by step: the scanning loop for singles, when to add pencil marks, which techniques to try in which order, and what to do when you are stuck.

Sudoku Techniques: The Complete List in Learning Order

Every sudoku technique you need, from full house and hidden singles to X-Wing, XY-Wing, and simple coloring, in the order to learn them, with a guide for each.

Sudoku Hints: How to Use Them Without Spoiling the Puzzle

The three kinds of sudoku hint, which one actually helps you improve, and how technique hints work in Sudoku Royale's Practice mode.

How to Play Sudoku on iPhone, Even One-Handed

How to play sudoku on iPhone: entering digits, notes, mistakes, settings, and how to hold the phone for comfortable one-handed play.

Number First vs Cell First: Fastest Sudoku Input

Cell first or number first? How each sudoku input works, a speed ranking of input methods, faster note entry, and how to combine them on iPhone.

Stuck on a Sudoku? What to Try Next, Step by Step

Stuck on a sudoku? Work down this 7-step ladder, from a rescan for hidden singles to pairs and XY-Wings. A real worked example grid for every step, no guessing.

Sudoku Techniques in Order of Difficulty (With Data)

Every sudoku technique ranked from easiest to hardest, with example grids and data from 457,000 graded puzzles showing what each difficulty level really needs.

Can You Solve Sudoku Without Guessing? Yes, Here's How

A proper sudoku never needs a guess. Why logic always works on a puzzle with one solution, what to do instead of guessing, and when trying a number counts as logic.

How to Solve Sudoku When There Are Two Options Left

A cell with two candidates is not a coin flip. Four logical ways to turn two options into a certain answer, each shown on a real example grid.

Sudoku Stuck With Only Pairs Left? 3 Ways Out

Every empty cell is down to two candidates and nothing works? How BUG+1, the unique rectangle, and the XY-Wing break a board full of pairs, with real examples.

How to Find a Mistake in Sudoku (Without Starting Over)

The two signs that your sudoku has a wrong digit, how to trace it back, and the habits that stop mistakes before they spread. With two example grids.

App Comparisons & Reviews

Best Sudoku Apps in 2026: iPhone, iPad and Android

Best sudoku apps in 2026 for iPhone, iPad and Android, compared: ad-free picks, offline play, iPad tips, and a 10-point checklist for choosing.

Best Multiplayer Sudoku Apps & Sites

The best ways to play sudoku with other people: live 1v1 duels, playing with friends, group races, turn-based apps, and tips for sudoku for two.

Best Apps for Competitive Sudoku Players

Where to play competitive sudoku in 2026: ranked apps, live races, online contests and the World Championship, plus how ratings work and tips to win.

Best Sudoku App for Hard Puzzles and Advanced Players

The best sudoku apps for advanced solvers: Master and Extreme levels, technique drills, a coach that finds your weak spots, and variant puzzles compared.

Best Alternatives to Sudoku.com in 2026

Tired of ads? The best Sudoku.com alternatives ranked: Sudoku Royale, Good Sudoku, Brainium, NYT Sudoku, sudoku.coach, and more.

Best Alternatives to Sudoku Face Off

Sudoku Face Off is turn-based and basic. Here are the best alternatives for real-time competitive multiplayer sudoku, solo puzzle volume, and learning.

Best Free Sudoku Apps With No Ads (2026)

The best free sudoku apps with no ads and no in-app purchases, what free really means, and how to check any app for ads before you download it.

Best Alternatives to NYT Sudoku in 2026

Don't want the NYT subscription? The best free and paid alternatives to NYT Sudoku ranked by puzzle quality, features, and price.

Best Alternatives to Good Sudoku

Looking beyond Good Sudoku? The best alternatives for technique training, free puzzles, and daily play, plus how its hints compare to a coach.

Brainium Sudoku Alternatives, Compared (2026)

Want more than Brainium Sudoku? Calm, ad-free alternatives compared, plus Sudoku Royale vs Brainium and Brainium vs Sudoku.com side by side.

Best-of Lists

Best Puzzle Games With No Ads on iPhone

The best ad-free puzzle games for iPhone, from free options like Sudoku Royale to premium picks like Monument Valley, The Room, and Good Sudoku.

Best Battle Royale Puzzle Games in 2026

The battle royale format meets puzzle games. Tetris 99, Sudoku Royale, and every battle royale puzzle game compared.

Sudoku Knowledge & Culture

Does Sudoku Go Diagonal? The Rule, Explained

No, classic sudoku ignores the diagonals. See a correct grid with repeated digits on its diagonal, plus quick answers to other sudoku rule questions.

How Many Sudoku Puzzles Are There?

6,670,903,752,021,072,936,960 valid grids, 5.47 billion essentially different ones, and a 17-clue minimum. Where each number comes from, with sources.

Sudoku World Records: Fastest Times and Titles

The fastest reported 9x9 sudoku solve, the Guinness records, and every World Sudoku Championship winner from 2006 to 2025, each with its source.

The Hardest Sudoku Ever, Graded

Arto Inkala's famous 21-clue puzzle, why it stumps pattern-based solvers, what our grader made of it, and whether it is really the hardest.

How Long Does a Sudoku Take? Real Solve Times

Median solve times by difficulty from 4,000+ real solves, plus which techniques each level needs, from a graded library of 457,048 puzzles.

Is Sudoku NP-Complete? A Plain-English Answer

Generalised sudoku is NP-complete (Yato and Seta, 2003), yet computers solve any 9x9 grid in milliseconds. What the result means and why both are true.

Is Sudoku Math or Logic? (And Why It Is 9×9)

Sudoku needs no arithmetic: the digits are just symbols. How the puzzle uses logic, where real mathematics comes in, and why the grid is 9 by 9.

History of Sudoku: Who Invented It and When

Sudoku was invented in the US in 1979, named in Japan in 1984 and made famous by The Times in 2004. The full, sourced timeline, including its French ancestors.

Sudoku Rules: The Only 3 Rules You Need to Know

The complete rules of sudoku explained in plain language. Every row, column, and 3x3 box must contain 1-9 exactly once.

Sudoku Variants: Killer, Diagonal, Samurai & More

A guide to every major sudoku variant, including Killer, Diagonal, Samurai, and Jigsaw, with rules and examples for each.

Is Sudoku Good for Your Brain? What Studies Show

An honest look at the research on sudoku, memory and dementia: what the big studies found, what they cannot show, and which popular claims are wrong.

Sudoku World Championship: History & How to Qualify

The World Sudoku Championship has run since 2006. Learn about its history, format, past winners, and how to qualify.

Which Sudoku Techniques Slow Players Down? Data from 243,104 Moves

Original data from 212 players: how long it takes to find naked singles, hidden singles and pointing pairs, how practice changes it, and which techniques 457,048 graded puzzles need. Free CSV.

The Mathematics Behind Sudoku

From constraint satisfaction to graph coloring: the fascinating mathematics that make sudoku puzzles work.

Sudoku vs Crossword: Which Is Better for Your Brain?

Both puzzles exercise your brain differently. Here's what the research says about sudoku vs crossword cognitive benefits.

Can a Sudoku Have More Than One Solution?

A proper sudoku has exactly one solution. What a puzzle with two looks like, the four-cell pattern that causes it, and how solvers use uniqueness as a technique.

Game Mode Guides

The Dojo: Sudoku Technique Drills in Sudoku Royale

How the Dojo in Sudoku Royale trains 13 sudoku techniques with lessons and Streak Rush drills, from Full House to XY-Wing, and how to use it to improve.

Sensei Royale: The Sudoku Coach in Sudoku Royale

How Sensei Royale finds the technique costing you the most time, gives you one assignment to fix it, and reviews your games move by move.

Unlimited Sudoku Puzzles: Six Levels From Easy to Extreme

How Classic works in Sudoku Royale: unlimited puzzles at six levels, how each level unlocks, hints that name the technique, offline play, and how long a puzzle takes.

The All-in-One Sudoku App: Every Way to Play in One Place

What an all-in-one sudoku app should include, and how Sudoku Royale covers it: six difficulty levels, a Daily Challenge, an 88-level Journey, technique lessons, a weekly belt league, and no ads.

Daily Sudoku: How It Works and How to Make It a Habit

How the daily sudoku works: weekly difficulty ramp, 30-second penalties, streaks and archive, plus how to make one puzzle a day a lasting habit.

Sudoku With Levels: How the 88-Level Journey Works

A sudoku level map with 88 levels in 10 chapters, from first steps to XY-Wing. How puzzles, lessons, drills, and gates work, how to skip ahead, and the Meijin title.

Sudoku Belts Explained: How the Weekly Belt League Works

The eight belts from White to Black, how every solved cell earns shurikens, and how weekly promotion and relegation work in Sudoku Royale.

Live Matches & Competitive Play

Battle Royale Sudoku: How It Works and How It Scores

Battle royale sudoku explained: one shared grid, claim cells before rivals do. How scoring, matchmaking, Battle Royale and Tournament rounds work.