Sudoku Tips & Strategies

From First Puzzle to Expert Solver

Beginner Intermediate Advanced General Tips

Sudoku isn't about guessing — it's about logic. Every puzzle has a unique solution that can be found through systematic techniques. Whether you're solving your first puzzle or tackling expert-level grids, these strategies will help you improve.

Beginner

Foundation Techniques

Master these first — they'll solve most easy and medium puzzles.

1. Scanning

The most fundamental technique. Scan each row, column, and 3×3 box to find where a specific number can go.

How to do it:

  1. Pick a number (start with 1)
  2. Look at each 3×3 box — where is that number already placed?
  3. For boxes missing that number, check which cells are blocked by the same number in the row or column
  4. If only one cell remains, that's where the number goes
Pro tip: Scan for numbers that appear most frequently first — they leave fewer possibilities.

2. Naked Singles

When a cell has only one possible candidate, it must be that number. This happens when eight of the nine numbers are already present in the cell's row, column, or box.

How to do it:

  1. Look at an empty cell
  2. Check its row — which numbers are already used?
  3. Check its column — which numbers are already used?
  4. Check its 3×3 box — which numbers are already used?
  5. If only one number (1-9) isn't eliminated, that's your answer

3. Hidden Singles

When a number can only go in one cell within a row, column, or box — even if that cell has other candidates — that's a hidden single.

How to do it:

  1. Focus on one row, column, or 3×3 box
  2. Pick a missing number
  3. Check each empty cell — can this number go here?
  4. If only one cell can hold that number, place it there
Pro tip: Hidden singles are "hidden" because the cell might have multiple candidates, but only one of them is unique to that cell in its group.

4. Using Pencil Marks (Candidates)

Write small numbers in empty cells to track which values are still possible. This is essential for intermediate and advanced techniques.

How to do it:

  1. For each empty cell, determine which numbers (1-9) are still possible
  2. Write these as small numbers in the corners or center of the cell
  3. As you solve, eliminate candidates that become impossible
  4. When a cell has only one candidate left, fill it in
Pro tip: You don't need to pencil mark every cell. Start with cells that have only 2-3 candidates — these are most likely to lead to solutions.
Intermediate

Pattern Recognition

These techniques help you eliminate candidates and break through stuck points.

5. Naked Pairs

When two cells in the same row, column, or box contain only the same two candidates, those numbers can be eliminated from all other cells in that group.

Example: If two cells in a row both contain only {4, 7}, then 4 and 7 must go in those two cells (in some order). You can remove 4 and 7 as candidates from every other cell in that row.

How to do it:

  1. Look for two cells in a row, column, or box with identical candidate pairs
  2. These two numbers are "locked" to those two cells
  3. Remove these candidates from all other cells in the same group
This extends to Naked Triples and Naked Quads — three cells with three candidates, four cells with four candidates, etc.

6. Hidden Pairs

When two candidates appear only in two cells within a row, column, or box, those cells must contain those two numbers — all other candidates in those cells can be eliminated.

Example: In a row, if 3 and 8 only appear as candidates in cells 2 and 5 (even though those cells have other candidates), you can remove all other candidates from cells 2 and 5.
Pro tip: Hidden pairs are the inverse of naked pairs — instead of finding cells with limited candidates, you're finding candidates with limited cells.

7. Pointing Pairs

When a candidate within a 3×3 box is limited to a single row or column, that candidate can be eliminated from that row/column outside the box.

Example: If the number 5 can only appear in the top row of a box, then 5 cannot appear in the rest of that row (outside the box). The 5 is "pointing" along the row.

8. Box/Line Reduction

The reverse of pointing pairs. When a candidate in a row or column is confined to a single box, eliminate that candidate from other cells in that box.

Example: If the number 6 in row 4 can only appear in the middle box, then 6 can be removed from all other cells in that box (rows 5 and 6 of that box).
Advanced

Expert Techniques

For the toughest puzzles. These require careful candidate tracking.

9. X-Wing

When a candidate appears in exactly two cells in two different rows, and these cells line up in the same two columns, you can eliminate that candidate from all other cells in those columns.

Visual: Picture four cells forming a rectangle. If a number can only go in the corners of this rectangle (two options per row), the number must occupy two diagonal corners. Either way, it eliminates that number from the rest of both columns.
Pro tip: X-Wing also works with columns pointing to rows. Look for the 2×2 pattern.

10. Swordfish

An extension of X-Wing using three rows and three columns. When a candidate appears 2-3 times in each of three rows, and these appearances align in exactly three columns, eliminate that candidate from other cells in those columns.

Pro tip: Swordfish is harder to spot. Focus on candidates that appear exactly 2-3 times in multiple rows. It extends further to Jellyfish (4×4).

11. XY-Wing

Uses three cells, each with exactly two candidates. One "pivot" cell sees two "wing" cells. The wings share one candidate with the pivot but share a different candidate with each other. Any cell that sees both wings can't contain the shared candidate.

Pattern: Pivot = {A, B}, Wing 1 = {A, C}, Wing 2 = {B, C}. The candidate C can be eliminated from any cell that sees both wings.

12. Simple Coloring

Track a single candidate through chains of cells where it appears exactly twice in a row, column, or box. Color these cells alternating colors. If two cells of the same color see each other, that color is false — eliminate that candidate from all same-colored cells.

Pro tip: Start coloring with candidates that form long chains. The longer the chain, the more likely you'll find a contradiction or elimination.
General

Best Practices

Habits that make you a better solver.

🎯

Start Easy

Always scan for naked singles and hidden singles first. They're the quickest wins.

📝

Use Pencil Marks

For medium+ puzzles, note candidates. It prevents mistakes and reveals patterns.

🔄

Work Systematically

Scan all rows, then columns, then boxes. Don't jump around randomly.

🚫

Never Guess

Every cell can be solved logically. If you're stuck, you're missing something.

☕

Take Breaks

Stuck for 5+ minutes? Step away. Fresh eyes often spot what you missed.

📈

Progress Gradually

Master easy puzzles before jumping to hard. Build pattern recognition over time.

✅

Verify As You Go

Double-check each placement. One wrong number can make the puzzle unsolvable.

🧠

Practice Daily

Consistency beats intensity. A puzzle a day builds lasting skills.

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