Sudoku Step Solver
learn while you solve

Sudoku Solver — Step by Step, Every Technique Explained

The only solver that teaches you how — not just what the answer is

Enter any Sudoku puzzle and watch it get solved one step at a time, with every move explained in plain English. Covers all 16 standard techniques: Naked Single, Hidden Single, Naked Pair, Hidden Pair, Naked Triple, Pointing Pair, X-Wing, Swordfish, XY-Wing, XYZ-Wing, Unique Rectangle, BUG+1, W-Wing, Nishio, and Forcing Chains.

▸ About the techniques & how the solver works

Tier 1 — Basic techniques

Naked Single: Only one digit can go in a cell — everything else is blocked by its row, column, or box. Hidden Single: A digit can only go in one cell within a row, column, or box, even if that cell has other candidates.

Tier 2 — Intermediate techniques

Naked Pair/Triple: Two or three cells sharing the same candidates lock those digits within a unit. Hidden Pair: Two digits that can only go in two cells force out all other candidates from those cells. Pointing Pair: If a digit in a box is confined to one row or column, it can be eliminated from that line outside the box.

Tier 3 — Advanced techniques

X-Wing: A digit confined to the same two columns across two rows can be eliminated from all other cells in those columns. Swordfish: The same principle across three rows and three columns. XY-Wing: A three-cell chain where both wings must contain the same digit — eliminating it from cells that see both wings. XYZ-Wing: A four-candidate variation of XY-Wing.

Tier 4 — Expert techniques

Unique Rectangle (Gordonian Rectangle): Uses the uniqueness constraint — a pattern that would give two solutions is impossible, so the digit breaking it is forced. BUG+1: When every cell has two candidates except one with three, logic forces the answer. W-Wing: Two bivalue cells connected by a strong link force eliminations in cells that see both.

Tier 5 — Diabolical techniques

Nishio: Assume a candidate is placed; if it causes a contradiction after propagation, eliminate it. Forcing Chains: Test both options of a bivalue cell — if both branches agree on an outcome, that outcome is certain. Bifurcation: A guided guess on the cell with fewest options, used only when all logic is exhausted.

Sudoku Solver: rules, how to use it, tips

Fill the grid so every row, column and box contains each digit exactly once.

The rules

  1. A standard grid is 9×9, split into nine 3×3 boxes. Here you can also play 4×4, 6×6 and 12×12.
  2. Write one digit in every empty cell — 1 to 9 on a 9×9 grid (1 to N on an N×N grid).
  3. No digit may repeat in any row, any column or any box.
  4. The digits already printed (the givens) cannot be changed. A good puzzle has exactly one solution.

Using the solver

  1. Type or paste the puzzle — use Import puzzle string for an 81-character line of digits and dots.
  2. Press Solve step by step. Each move names its technique (Naked Single, Pointing Pair, X-Wing …) and highlights the cells involved.
  3. Use the arrows to move one step at a time, or Solve all remaining.
  4. Every technique is explained on the Sudoku techniques page.

Tips

The full guide, with a worked example and common mistakes: How to play Sudoku.

Questions

How many givens does a Sudoku need?

A standard 9×9 Sudoku needs at least 17 givens to have a unique solution. Most newspaper puzzles give 25 to 30.

Is Sudoku a maths puzzle?

No arithmetic is involved — the digits are just symbols. It is a logic puzzle about placement; letters or colours would work the same way.

What does Devilish mean here?

The hardest level. Devilish puzzles need intermediate and advanced techniques such as pairs, X-Wings and chains, not just singles.

Can I check a puzzle from a newspaper?

Yes. Type it into the Sudoku Solver and it solves it one step at a time, naming the technique for every move.

Why do 6×6 and 12×12 grids have rectangular boxes?

Their boxes are 2×3 and 3×4, because 6 and 12 are not square numbers. The rule is the same: each box holds each digit once.

Related