Sudoku Assistant — Learn Sudoku Solving Techniques

Enter a Sudoku puzzle and learn step-by-step how to solve it. The assistant analyzes your puzzle, explains the technique needed for each step, and teaches you solving strategies. 100% client-side — your puzzle never leaves your browser.

Analysis & Steps
Enter a puzzle and click "Analyze & Explain" to begin.

How to Use the Sudoku Assistant

  1. Enter your puzzle — click cells and type numbers, or paste an 81-digit string.
  2. Click "Analyze & Explain" — the assistant will explain what it found and the technique needed.
  3. Click "Next Step" — apply the next logical step with a full explanation.
  4. Repeat until the puzzle is solved, learning techniques along the way.

How It Works

The Sudoku Assistant uses a constraint-satisfaction engine to solve puzzles step by step. It maintains a candidate list for every empty cell — the set of numbers that could legally go there based on row, column, and box constraints. The assistant then applies logical techniques in order from simplest to most advanced.

For each step, the assistant identifies which technique is needed and explains the reasoning. This includes naked singles (a cell has one candidate), hidden singles (a number can only go in one place in a row/column/box), and advanced patterns like X-Wing, Swordfish, and XY-Wing. If a puzzle requires a technique not yet implemented, the assistant will indicate that manual solving is needed. Most puzzles up to expert level can be solved with the 17 techniques covered.

Techniques Reference

Technique Difficulty Description
Naked SingleBeginnerA cell has only one possible candidate — that number must go there.
Hidden SingleBeginnerA number can only go in one cell within a row, column, or box.
Naked PairIntermediateTwo cells in a unit share the same two candidates — eliminate them from other cells.
Naked TripleIntermediateThree cells collectively use only three candidates — eliminate from other cells.
Naked QuadIntermediateFour cells collectively use only four candidates — eliminate from other cells.
Hidden PairIntermediateTwo numbers only appear in the same two cells — remove other candidates from those cells.
Hidden TripleIntermediateThree numbers only appear in the same three cells — remove other candidates.
Hidden QuadIntermediateFour numbers only appear in the same four cells — remove other candidates.
Pointing Pair/TripleIntermediateA candidate in a box is restricted to one row or column — eliminate from that line outside the box.
Box/Line ReductionIntermediateA candidate in a row/column is restricted to one box — eliminate from other cells in that box.
X-WingAdvancedA candidate in two rows aligns in two columns — eliminate from those columns elsewhere.
SwordfishAdvancedExtension of X-Wing to three rows and three columns.
XY-WingAdvancedThree cells in a hinge pattern eliminate a shared candidate from cells seeing both pingers.
XYZ-WingAdvancedLike XY-Wing but the pivot has three candidates — eliminates the shared candidate.
Unique RectanglesAdvancedExploits the single-solution guarantee to eliminate candidates that would create multiple solutions.
Turbot FishAdvancedAn incomplete X-Wing pattern that still allows eliminations via strong/weak links.
Simple ColoringAdvancedChains a candidate with alternating colors — contradictory colors can be eliminated.

Tips for Solving Harder Puzzles

  • Always pencil in candidates — before attempting advanced techniques, make sure every empty cell has its full candidate list. Most mistakes come from missing candidates.
  • Work systematically — scan rows, columns, and boxes in order. Don't jump around randomly. Consistency helps you spot patterns.
  • Look for naked pairs first — before trying X-Wing or Swordfish, exhaust all naked and hidden pair/triple/quad possibilities. They're easier to spot and solve more puzzles.
  • Use process of elimination — when stuck, focus on one number at a time. Go through 1–9 and see where each number can and cannot go in every row, column, and box.
  • Coloring helps visualize chains — for advanced techniques, mentally or physically mark cells with alternating colors to trace strong and weak links.
  • Don't guess — guessing leads to contradictions and wasted time. If you're stuck, there's a logical technique you haven't tried yet.
  • Practice daily — pattern recognition improves with repetition. Even 10 minutes a day will noticeably improve your solving speed within weeks.

Solving Techniques Reference

Beginner

Naked Single

When a cell has only one possible candidate remaining, that number must go there.

Example: If a cell can only be 5 (all other numbers 1-9 are present in its row, column, or box), then it must be 5.
Tip: This is the most basic technique. Start by scanning each empty cell to see if only one number fits.
Beginner

Hidden Single

When a number can only go in one cell within a row, column, or box, it must go there — even if that cell has other candidates.

Example: If the number 7 can only appear in one cell of row 3, then that cell must be 7, even if it shows other possibilities.
Tip: Check each row, column, and box to see if any number has only one possible position.
Intermediate

Naked Pair

When two cells in the same unit (row, column, or box) contain the same two candidates, those two numbers are locked to those cells. You can eliminate these candidates from other cells in that unit.

Example: If two cells in a row both have candidates {3, 7}, then no other cell in that row can be 3 or 7.
Tip: Look for pairs of cells with identical candidate lists. This technique removes possibilities from neighboring cells.
Intermediate

Naked Triple

When three cells in the same unit collectively contain only three candidates, those numbers are locked to those cells. Eliminate these candidates from other cells in that unit.

Example: If cells have candidates {1,2}, {2,3}, and {1,3}, together they use only 1, 2, and 3. Remove these from other cells in the unit.
Tip: The three cells don't each need all three candidates — they just need to collectively use exactly three numbers.
Intermediate

Hidden Pair

When two numbers only appear as candidates in the same two cells within a unit, those cells must contain those two numbers. Remove all other candidates from those cells.

Example: If 4 and 8 only appear in cells A and B of a box, then A and B must be {4,8}. Remove any other candidates from A and B.
Tip: Unlike Naked Pairs, Hidden Pairs may be "hidden" among other candidates in the cells.
Intermediate

Naked Quad

When four cells in the same unit collectively contain only four candidates, those numbers are locked to those cells. Eliminate these candidates from other cells in that unit.

Example: If cells have candidates {1,2}, {2,3}, {3,4}, and {1,4}, together they use only 1, 2, 3, and 4. Remove these from other cells in the unit.
Tip: Naked Quads are rare. Before looking for them, try Naked Triples first.
Intermediate

Hidden Triple

When three numbers only appear as candidates in the same three cells within a unit, those cells must contain those three numbers. Remove all other candidates from those cells.

Example: If 2, 5, and 9 only appear in cells A, B, and C of a row, then A, B, and C must be {2,5,9}. Remove any other candidates from these cells.
Tip: Hidden Triples are harder to spot than Naked Triples because the candidates may be hidden among other possibilities.
Intermediate

Hidden Quad

When four numbers only appear as candidates in the same four cells within a unit, those cells must contain those four numbers. Remove all other candidates from those cells.

Example: If 1, 3, 6, and 8 only appear in cells A, B, C, and D of a box, then these cells must be {1,3,6,8}. Remove any other candidates.
Tip: Hidden Quads are very rare. If you're stuck, double-check your candidate lists before looking for this technique.
Intermediate

Pointing Pair / Triple

When a candidate in a box is restricted to a single row or column, it can be eliminated from that row or column outside the box.

Example: If the number 5 in box 1 only appears in row 1, then 5 can be removed from all other cells in row 1 (outside box 1).
Tip: This technique bridges box constraints with row/column constraints.
Intermediate

Box/Line Reduction

When a candidate in a row or column is restricted to a single box, it can be eliminated from other cells in that box.

Example: If the number 3 in column 5 only appears in box 8, then 3 can be removed from all other cells in box 8.
Tip: This is the reverse of Pointing Pairs — look at rows/columns instead of boxes.
Advanced

X-Wing

When a candidate appears in exactly two cells in each of two different rows, and these cells align in the same two columns, the candidate can be eliminated from all other cells in those two columns.

Example: If number 2 only appears in columns 3 and 7 of both row 2 and row 8, then 2 can be removed from all other cells in columns 3 and 7.
Tip: X-Wing creates a rectangle pattern. The same logic applies swapping rows and columns.
Advanced

Swordfish

An extension of X-Wing to three rows and three columns. When a candidate in three rows is restricted to the same three columns, eliminate it from those columns elsewhere.

Example: If number 5 in rows 1, 4, and 7 only appears in columns 2, 5, and 9, remove 5 from other cells in those columns.
Tip: Swordfish is rarer than X-Wing. Look for it when easier techniques stall.
Advanced

XY-Wing

Three cells form a hinge pattern: the pivot has candidates {X,Y}, and two pingers have {X,Z} and {Y,Z}. Any cell seeing all three cannot be Z.

Example: Pivot at R5C5 with {2,3}, pingers at R5C1 with {2,7} and R1C5 with {3,7}. Any cell seeing both pingers cannot be 7.
Tip: The pivot must see both pingers, and the pingers must not see each other directly (except through the pivot).
Advanced

XYZ-Wing

Like XY-Wing, but the pivot has three candidates {X,Y,Z}. One pinger has {X,Z} and the other has {Y,Z}. Any cell seeing all three cannot be Z.

Example: Pivot at R5C5 with {2,3,7}, pinger at R5C1 with {2,7} and pinger at R1C5 with {3,7}. Any cell seeing both pingers cannot be 7.
Tip: The pivot must see both pingers. The "Z" candidate (the one eliminated) is the one shared by all three cells.
Advanced

Unique Rectangles

If four cells in a rectangle formation share two candidates, the puzzle would have multiple solutions. To avoid this, at least one cell must contain a third candidate, which can be eliminated from other cells seeing both corners.

Example: Cells R1C1 and R1C9 have {1,2}, and R9C1 has {1,2,5}. If R9C9 also had only {1,2}, there would be two valid solutions. So R9C9 cannot be 1 or 2 — it must resolve differently.
Tip: Unique Rectangles exploit the guarantee that a valid Sudoku has exactly one solution.
Advanced

Turbot Fish

A Turbot Fish (or Sashimi X-Wing) is an incomplete X-Wing pattern that still allows eliminations. When a candidate in two rows shares columns but one row has an extra position, the extra position can sometimes be eliminated.

Example: Number 4 appears in columns 3 and 7 of row 2, but in row 8 it appears in columns 3, 5, and 7. The cell at R8C5 can be eliminated because it sees both corners of the incomplete rectangle.
Tip: Turbot Fish is essentially a chain of strong/weak links. Look for it when X-Wing doesn't quite fit.
Advanced

Simple Colorings

For a candidate that appears in only two cells per unit, chain them with alternating colors. If two cells of the same color see each other, that color is false and can be eliminated.

Example: Color cells alternately blue/red. If two blue cells are in the same row, all blue cells are wrong — eliminate them.
Tip: Coloring helps visualize strong/weak links between candidate positions.

Technique Difficulty Progression

1

Start Here

Master Naked Singles and Hidden Singles first. These solve most easy puzzles completely.

2

Build Skills

Learn Naked/Hidden Pairs, Triples, and Pointing Pairs. These tackle medium puzzles and build pattern recognition.

3

Level Up

Master Box/Line Reduction and X-Wing. These unlock hard puzzles and improve logical reasoning.

4

Expert Level

Swordfish, XY-Wing, XYZ-Wing, Unique Rectangles, and Coloring. These conquer expert puzzles and complete your technique arsenal.

Frequently Asked Questions

The assistant now implements 17 techniques covering beginner through advanced difficulty. If a puzzle requires a technique not yet implemented (like Jellyfish or Forcing Chains), the assistant will indicate that manual solving is needed. Most puzzles up to expert level can be solved with the covered techniques.

The assistant assumes the puzzle has a unique solution. If you enter an invalid puzzle with multiple solutions, some steps may not work correctly. Use puzzles from trusted sources for best results.

Both! The explanations teach you the techniques. After following several puzzles, you'll recognize patterns and solve independently. The reference section serves as a permanent study guide.

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