Learn Sudoku
New to Sudoku? Start with the three rules. Explore rows, columns and boxes on example boards, then find the next number in a practice puzzle.
Sudoku Rules: A 3-Minute Guide
Learn the three rules for rows, columns and 3×3 boxes, and two ways to find your first number on an example board.
BeginnerHow to Use Sudoku Candidate Notes
Learn how to note the possible numbers in each empty cell and use a Naked Pair among those candidates to find your next number on an example board.
BeginnerDo You Need Trial and Error to Solve Sudoku?
Explore trial and error in a cell with two candidates, why testing an assumption is costly in this app, and the logic you can use instead, with an example board.
BeginnerStuck on Sudoku? A 7-Step Checklist
Follow seven checks when you cannot find another number, and learn to scan boxes for a number instead of focusing on a cell, with an example board.
BeginnerUnderstanding Sudoku Hints in 4 Steps
Learn what this app’s hints do and how to work backward from a revealed number to understand it and find it yourself next time, with an example board.
BeginnerWhy Sudoku Difficulty Varies Between Apps
Learn how DailySudoku sets difficulty and why puzzles at the same level can feel different, with measured results and two example boards.
Techniques
Which Candidates Can X-Wing Remove? A Complete Guide to Rows and Columns
Distinguish row-based and column-based X-Wings in rectangles formed by candidates for one number, and use coordinates to check where you can remove candidates.
IntermediateWhere Can You Use a Skyscraper When Locked Candidates Stop Helping?
Explore the difference between locked candidates and Skyscraper through candidate positions, and find candidates you can remove only when the base and top conditions hold.
IntermediateHow Does XY-Wing Differ from X-Wing, and Where Can You Remove Candidates?
Find an XY-Wing by linking the candidates in a pivot and two pincers, and compare its conditions and elimination cells with X-Wing and Skyscraper.
AdvancedColoring: What Can Same-Color Conflicts and Two-Color Traps Remove?
Distinguish wraps and traps in Simple Coloring through original examples, and read colors, symbols and lines together to find the reasons for eliminations.
AdvancedBUG+1: Why Must You Assume a Unique Solution?
Check the candidate counts, unit conditions and uniqueness assumption for BUG+1, and explore why its conclusion fails in a counterexample with multiple solutions.
AdvancedIntroduction to AIC: What Can Alternating Strong and Weak Links Remove?
Learn to read candidates as nodes in an AIC link graph, understand solid and dashed lines, and remove candidates from cells that see both endpoints.