Every technique from beginner to expert — when to use it, how it works, and a link to the full guide. Bookmark this page before your next puzzle session.
Full explanation: Sudoku Rules · How to Play
When: A row, column, or box has exactly one empty cell
How: Place the one missing digit — no calculation needed
When: Looking for where a specific number can go in a box
How: Cross out rows/columns that already contain that number; remaining cell is the answer
When: A cell has only one candidate remaining
How: That one candidate must go in the cell — eliminate by row, column, and box
When: A digit can only appear in one cell within a unit (row/column/box)
How: Even if the cell has multiple candidates, place that digit — it has nowhere else to go
When: Two cells in the same unit share exactly the same two candidates
How: Those two numbers must go in those two cells → eliminate both from all other cells in that unit
When: Three cells in a unit collectively contain only three candidates
How: Those three numbers are locked to those three cells → eliminate all three from other cells in the unit
When: A candidate in a box appears only in one row or column within that box
How: Eliminate that candidate from the rest of the same row/column outside the box
When: A candidate in a row/column appears only within one box
How: Eliminate that candidate from other cells in that box (reverse of Pointing Pair)
When: A candidate appears in exactly two cells in each of two rows, and both rows share the same two columns
How: The candidate must go in one of two diagonal pairs → eliminate from all other cells in those two columns
When: Three cells form a Y-shape: a pivot cell sharing candidates with two "wing" cells, all linked by pairs
How: Any cell that "sees" both wings cannot contain their shared candidate — eliminate it
When: A candidate appears in exactly two or three cells in each of three rows, and all those cells fall in only three columns
How: Like X-Wing but across three rows → eliminate the candidate from all other cells in those three columns
When: You have filled in pencil marks and need a systematic approach
How: Systematically remove impossible candidates from each cell using all known placements and constraints
For medium difficulty and above, always fill in candidate numbers in empty cells before applying techniques. Without pencil marks, Naked Pairs and Pointing Pairs are nearly impossible to spot. See the complete Pencil Marks Guide.
The Last Free Cell is the easiest: when a row, column, or box has only one empty cell, the missing number goes there with zero calculation. After that, Crosshatching and Naked Singles are the next simplest — they solve all easy puzzles combined.
Medium puzzles require Naked Pairs and Pointing Pairs in addition to the beginner techniques. Learn to fill in pencil marks (candidate notes) before attempting eliminations — this is essential for intermediate play.
X-Wing is the most commonly applicable advanced technique — it unlocks many hard puzzles. Y-Wing is more complex but very powerful. Swordfish is rarer but useful for expert puzzles. Together these three handle most hard and expert Sudoku puzzles.
No. For easy and medium puzzles, the four beginner techniques are sufficient. Naked Pairs and Pointing Pairs handle most hard puzzles. X-Wing and Y-Wing cover most expert puzzles. Only the hardest computer-generated puzzles require Swordfish or more advanced patterns.
Always work from simple to complex. Start by scanning for Last Free Cells, then Naked Singles, then Hidden Singles. If no singles are found, look for Naked Pairs, then Pointing Pairs, then Box-Line Reduction. Only advance to X-Wing or Y-Wing when simpler techniques are exhausted.