Sudoku 
Games Like Sudoku: Best Logic Puzzles and Number Games to Try
A comprehensive guide to the best games like Sudoku, including number games, math puzzles, brain games, apps, and Sudoku variants.
Sudoku Dark Mode: Play Online in a Low-Glare Theme
Play classic Sudoku in dark mode and learn how the site-wide sun/moon toggle works across all our Sudoku games.
Sudoku Pencil Marks: What They Are and How to Use Them
Learn pencil marks, candidates, manual notes, Auto Notes, and the solving workflow that makes harder Sudoku puzzles manageable.
The Complete Sudoku Variations List — Every Type of Sudoku Explained
From Classic and Killer to Thermo, Arrow, Anti-Knight, and dozens more — rules, tips, and free playable games for 100+ sudoku variants organised by category.
Electronic Sudoku: Handheld Devices vs. Online Puzzles
A complete guide to electronic sudoku — dedicated handheld devices, tablets, apps and free online puzzles. Find the perfect option for any sudoku lover.
Sudoku Techniques: Complete List of Solving Strategies
A comprehensive roundup of Sudoku techniques, from singles and pairs to fish, wings, chains, colouring, uniqueness, ALS, and expert-level solving patterns.
Sudoku Strategies for Beginners: The Step-by-Step Guide
A beginner-friendly Sudoku strategy guide covering scanning, cross-hatching, singles, pencil marks, pairs, common mistakes, and a repeatable solving routine.
Sudoku Terms: Complete Glossary of Definitions & Terminology
A complete Sudoku glossary covering grid terms, candidate notation, solving techniques, fish patterns, chains, uniqueness terms, variants and common abbreviations.
Mathematics of Sudoku: The Logic Behind a 9x9 Grid
How classic Sudoku works mathematically: constraints, combinations, uniqueness, solving logic, exact cover, symmetry, clue counts, and why it is not arithmetic.
Sudoku Difficulty Levels: Easy to Expert Explained
A comprehensive guide to Sudoku difficulty levels: easy, medium, hard, expert and extreme puzzles, rating systems, clue counts and techniques.
Sudoku Mistakes: Common Errors and How to Avoid Them
Learn the mistakes Sudoku players make most often, how to fix a bad grid, and what mistake counters, no-mistake play, and unlimited mistakes mean.
Rules of Killer Sudoku: How to Play
Learn Killer Sudoku rules, cage sums, no-repeat cages, beginner examples, the Rule of 45, and the first solving steps.
Killer Sudoku Tips and Strategies: Complete Roundup Guide
A complete roundup of Killer Sudoku tips: cage sums, combinations, the rule of 45, innies, outies, notes, pairs, and advanced solving habits.
Killer Sudoku Combinations: Complete Chart and Solving Guide
Complete Killer Sudoku combination charts for 2, 3 and 4-cell cages, plus minimum sums, complements, notation tips and worked examples.
Rule of 45 Sudoku: Complete Killer Sudoku Guide
Master the Rule of 45 in Killer Sudoku with innies, outies, cage totals, multi-house examples, and common solving mistakes.
X-Wing Sudoku Technique: How to Find & Use It (With Examples)
Master the X-Wing pattern — the key advanced technique for eliminating candidates and unlocking hard sudoku puzzles. Step-by-step guide with visual examples.
Naked Pairs in Sudoku: How to Find & Use Them (With Examples)
Master the Naked Pairs technique — the essential intermediate strategy for eliminating candidates and simplifying your sudoku grid. Step-by-step guide with diagrams.
Hidden Pairs in Sudoku: How to Find & Use Them (With Examples)
Master the Hidden Pairs technique — the powerful intermediate strategy for stripping extra candidates from cells and unlocking stuck sudoku grids. Step-by-step guide with diagrams.
XY-Wing in Sudoku: How to Find & Use This Technique (With Examples)
Master the XY-Wing pattern — the elegant advanced technique using three bivalue cells to eliminate candidates across the grid. Step-by-step guide with diagrams.
Pointing Pairs in Sudoku: How to Find & Use This Technique (With Examples)
Master the Pointing Pairs technique — exploit box-line interactions to eliminate candidates along rows and columns. Step-by-step guide with before-and-after diagrams.
Box/Line Reduction in Sudoku: How to Master the Claiming Technique (With Examples)
Learn Box/Line Reduction (Claiming) — the inverse of Pointing Pairs. When a candidate in a row or column is confined to one box, eliminate it from the rest of that box.
Swordfish in Sudoku: Strategy & Technique Explained (With Examples)
Master the Swordfish technique — an advanced fish pattern using three rows and three columns to eliminate candidates across a wider area than an X-Wing.
Jellyfish in Sudoku: Strategy & Technique Explained (With Examples)
Master the Jellyfish technique — an expert-level fish pattern using four rows and four columns for powerful candidate eliminations across the grid.
Naked Triples in Sudoku: How to Find & Use Them (With Examples)
Master the Naked Triples technique — an intermediate strategy that uses three cells and three candidates to eliminate possibilities from your Sudoku grid.
Hidden Triples in Sudoku: How to Find & Use Them (With Examples)
Master the Hidden Triples technique — an intermediate strategy that finds three candidates restricted to three cells and strips away the extras.
Hidden Singles in Sudoku: How to Find & Use Them (With Examples)
Master the Hidden Singles technique — the most fundamental Sudoku strategy that finds a candidate appearing in only one cell of a row, column, or box.
Naked Singles in Sudoku: How to Find & Use Them (With Examples)
Master the Naked Singles technique — the simplest Sudoku strategy where a cell has only one candidate remaining, making it the easiest digit to place.
XYZ-Wing in Sudoku: How to Find & Use This Advanced Technique (With Examples)
Master the XYZ-Wing technique — an advanced Sudoku strategy that extends the XY-Wing with a three-candidate pivot to eliminate candidates from cells that see all three.
W-Wing in Sudoku: How to Find & Use This Advanced Technique (With Examples)
Master the W-Wing technique — an advanced chain-based strategy that connects two bi-value cells through a strong link to eliminate candidates at a distance.
Skyscraper Technique in Sudoku: How to Find & Use This Elimination Pattern (With Examples)
Master the Skyscraper technique — a single-digit elimination pattern that uses two conjugate pairs sharing one base endpoint to remove candidates from distant cells.
Simple Colouring in Sudoku: How to Find & Use This Chain-Based Elimination Technique (With Examples)
Master Simple Colouring (Singles Chains) — build alternating colour chains along conjugate pairs for a single digit to eliminate candidates from cells that see both colours.
Unique Rectangles in Sudoku: How to Find & Use This Deadly-Pattern Elimination Technique (With Examples)
Master Unique Rectangles — use uniqueness reasoning to spot deadly patterns and eliminate candidates from the roof cell in four easy steps.
Locked Candidates in Sudoku: How to Use Pointing & Claiming to Eliminate Candidates (With Examples)
Master the Locked Candidates technique — use box–line interactions to eliminate candidates with Pointing (Type 1) and Claiming (Type 2).
Almost Locked Sets (ALS) in Sudoku: The ALS-XZ Rule Explained (With Examples)
Master the ALS-XZ technique — use two Almost Locked Sets connected by a Restricted Common Candidate to eliminate candidates like an expert.
3D Medusa in Sudoku: Multi-Digit Colouring Explained (With Examples)
Master 3D Medusa — extend Simple Colouring across multiple digits via bivalue cells and conjugate pairs for powerful eliminations.
Sue de Coq in Sudoku: Two-Sector Disjoint Subsets Explained (With Examples)
Master Sue de Coq — use Almost Locked Sets at the intersection of a line and box to eliminate candidates from both sectors simultaneously.
Remote Pairs in Sudoku: Chain Bivalue Cells to Eliminate Candidates (With Examples)
Master Remote Pairs — chain bivalue cells sharing the same two candidates across connected houses and eliminate both digits from any cell that sees both ends of the alternating chain.
Finned X-Wing in Sudoku: How the Extra Fin Restricts Eliminations (With Examples)
Master the Finned X-Wing — find an almost-perfect X-Wing, locate the fin cell that breaks the pattern, and eliminate the target digit from cells that see both the fin and the X-Wing column.
Finned Swordfish in Sudoku: How to Find and Apply This Advanced Fish Technique
Master the Finned Swordfish — spot a near-perfect Swordfish pattern, identify the fin cell that breaks it, and eliminate the target digit from cells that see both the fin and the Swordfish column.
Sudoku vs Chess: Which Is Better for Your Brain?
Compare sudoku and chess for logic, memory, focus, mood, learning curve, and everyday brain training.
History of Sudoku: Origins, Timeline and Global Rise
Trace Sudoku from Latin squares and Number Place to Nikoli, Wayne Gould, global newspapers, apps, variants, and modern online play.
New York Times Sudoku Alternatives
A positive comparison of NYT Sudoku alternatives, with our free variants, difficulty levels, 17-clue puzzles, and hardest Sudoku picks first.