Medium Sudoku — Learn Candidate Eliminations

Medium Sudoku: inspect an intersection

When medium Sudoku has no single, select one digit and compare its possible positions within a box and a line. If every position in the source lies in their intersection, the crossing unit cannot place that digit outside it. Medium Sudoku asks you to prove where a digit is confined, without guessing its exact cell.

Medium Sudoku: reserve two candidates

A medium Sudoku pair uses two cells in one unit with only the same two digits between them. Those digits occupy both cells, so remove them from the rest of the unit. Keep the pair undecided, then scan again for a single. An extra candidate in either cell breaks this argument.

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.

Use complete candidates, locked candidates and naked pairs when singles stop. A deduction may remove a note before it fills a cell.

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.