Hard Sudoku — Prove the Next Deduction

Hard Sudoku: keep the premises complete

Hard Sudoku can require a hidden pair, a triple or an X-Wing. Inspect full candidates and the whole relevant unit before deleting anything. Hard Sudoku is not a promise that every advanced technique appears in each puzzle; the example below demonstrates one pattern you may encounter.

Hard Sudoku: return to simple moves

After a candidate elimination in hard Sudoku, look for singles again. The next useful deduction can be simpler than the previous one. Hints show observations and reasons before application, while the full replay explains the fixed original route. An incorrect entry must be corrected before treating later deductions as trustworthy.

Find your next challenge

Difficulty describes the logic in the verified walkthrough, rather than the number of empty cells. Start with certain placements, then learn to remove candidates before taking on a longer sequence.

Work with hidden pairs, triples or X-Wing as needed by the puzzle. Hard has a complete logical walkthrough; its label does not promise every advanced pattern appears in every puzzle.

Learn one move. Find the next.

Each guide tackles a specific problem with an original grid, a reason for the move, a counterexample and exercises. Choose the task that matches the place you have stopped.

• How to Solve Sudoku: A Practical Beginner’s Guide

  Learn the three constraints, a safe first move, and the difference between a single candidate and a single position.

• How to Use Pencil Marks Without Filling the Board with Clutter

  Write complete candidates, clean notes after a move, and avoid treating a missing note as proof.

• Naked Single vs. Hidden Single: Find the Difference on a Real Grid

  Compare two kinds of certain moves with original diagrams and exercises.

• Sudoku X-Wing Explained: Spot the Pattern, Prove the Elimination

  Check the exact row and column conditions, prove a deletion, and reject a misleading rectangle.

• Stuck on Hard Sudoku? A Logical Routine Before You Guess

  Check your entries and candidates, inspect singles and pairs, and use a staged hint to continue.

• Your Daily Sudoku: Saved Progress, Walkthroughs and Clear Prints

  Keep the same daily puzzle, review its steps, and print a clean original with a separate answer.

Sudoku rules: three constraints, one certain move

Fill every row, column and 3×3 box with the digits 1 through 9 once each. Arithmetic is not required. A candidate is a possibility; a full-size entry is a number you have decided. Before placing a digit, check all three constraints.

Sudoku controls leave room for reasoning

Select a cell, then enter 1–9 or use the number pad. Notes keeps small candidates separate from entries. Erase removes an entry or note; Undo restores the previous action and the notes cleaned by that action. Check compares entered digits with the solution. A hint first shows where to look, then why the move works, before you apply it.

Continue on this device

Progress is saved locally in this browser. Free and daily puzzles keep separate progress for each difficulty. Pausing or leaving the active page stops the timer. Changing language does not create a different puzzle. Clearing browser data or using another device does not transfer your save.

Take a Sudoku puzzle to paper

Choose a verified original puzzle and keep its ID with your printout. The original shows only the givens; current progress includes your entered digits. Answers are separate so you can decide when to look.