From the rulebook
Solving guides
Learn how each puzzle works and the techniques that crack the hard ones. Every guide is free and pairs with puzzles you can play right now.
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How to Solve Sudoku
Learn how to solve Sudoku, from the basic rules to scanning, pencil marks, naked pairs and pointing pairs. A clear, step-by-step strategy guide for beginners and improvers.
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How to Solve X-Sudoku
Learn how to solve X-Sudoku, also called diagonal Sudoku. The classic 1 through 9 rules plus both diagonals, with scanning, pencil marks and diagonal-specific tactics.
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How to Solve Killer Sudoku
Learn how to solve Killer Sudoku, also called sum Sudoku. The classic 1 through 9 rules plus cage sums, with the rule of 45, cage combinations and the no-repeat-in-cage tactic.
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How to Solve Calcudoku
Learn how to solve Calcudoku, also called KenKen or Mathdoku. The once-per-row-and-column rule plus arithmetic cages, with cage combinations, the no-box rule and operation-specific tactics.
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How to Solve Crossmath
Learn how to solve Crossmath, the arithmetic crossword puzzle. Place number tiles so every across and down equation is true, with constraint-first tactics, crossing checks and operator shortcuts.
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How to Solve Kakuro
Learn how to solve Kakuro, also called cross sums. The fill-the-runs rules plus magic combinations, the no-repeat-in-a-run tactic, crossing checks and the box-sum trick.
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How to Solve Ripple Effect
Learn how to solve Ripple Effect, also called Hakyuu. Fill each room with 1 up to its size while equal numbers keep their distance, with room-size tactics, the spacing rule and crossing checks.
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How to Solve Star Battle
Learn how to solve Star Battle, also called Two Not Touch. Place stars so every row, column and region has the same count and no two stars touch, with the no-touch rule, region tactics and crossing checks.
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How to Solve Aquarium
Learn how to solve Aquarium. Fill each bold-outlined region with water so every row and column count matches its clue, using the level rule, gravity, and cross-line deduction.
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How to Solve Star Circle
Learn how to solve Star Circle. Fill the grid with stars and circles, keep every row and column balanced, avoid three matching symbols in a row, and use same or different clues between cells.
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How to Solve Number Loop
Learn how to solve Number Loop, also called Slitherlink. Draw one closed loop where every number matches the edges around it, with the zero rule, corner tactics, the two-ends-per-dot check and propagation.
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How to Solve Nonograms
Learn how to solve Nonograms, also called Picross, Hanjie or griddlers. Use the row and column clues to reveal pixel art, with the overlap trick, marking empties, edge anchors and cross-referencing.
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How to Solve Code Grid
Learn how to solve Code Grid. Rearrange the source grid's digits into the hidden solution using exact, misplaced and absent clue counts for every row and column.
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How to Solve Heyawake
Learn how to solve Heyawake. Shade black cells to match every room number, keep blacks apart, keep every white cell connected, and break long white lines.
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How to Solve Standout
Learn how to solve Standout. Shade cells so no number repeats unshaded in any row or column, keep shaded cells apart, and keep every unshaded cell connected.