How to Play Sudoku

That is it. One rule. Everything else — every technique, every strategy, every puzzle — is a consequence of that single constraint applied across 81 cells. You do not need to memorise anything else to play Sudoku. You just need to practice seeing how the rule limits where each number can go.

A Sudoku puzzle is a 9×9 grid — 81 cells arranged in 9 rows and 9 columns. The grid is further divided into nine 3×3 boxes (sometimes called regions or blocks). These are the thick-bordered squares you see: three across and three down.

Every cell belongs to exactly three groups simultaneously:

• One row (horizontal, numbered 1–9 from top to bottom)
• One column (vertical, numbered 1–9 from left to right)
• One 3×3 box (the thick-bordered region it sits inside)

When you place a number in a cell, that number is instantly forbidden in the other 8 cells of its row, the other 8 cells of its column, and the other 8 cells of its box — up to 20 cells affected by a single placement. That cascading effect is what makes Sudoku solvable.

When you open a Sudoku puzzle, some cells are already filled with numbers. These are called givens (or clues). You cannot change them. Your job is to fill in the remaining empty cells.

For any empty cell, the candidates are the digits 1–9 that are not yet forbidden by the cell's row, column, or box. A cell might have 7 candidates early in the puzzle; as the puzzle fills in, that list narrows until only one digit remains — and then you know the answer.

In this 3×3 box the given numbers are 1, 3, 4, 5, 6, 8. The missing numbers are 2, 7, and 9. Each of the three empty cells must hold one of these — but which cell gets which number depends on the row and column constraints from the rest of the grid.

1. 1

   Scan the grid for obvious moves

   Look for rows, columns, or boxes that are nearly complete — 7 or 8 cells already filled. The fewer candidates left, the easier the deduction. Nearly-complete groups often have a "last remaining cell" where only one digit can go.

2. 2

   Apply cross-hatching for each digit

   Pick one digit — say, 5. Find every row and column that already has a 5. Those rows and columns are "blocked" in every box they pass through. If a box does not yet have a 5, and the blocked rows and columns leave only one empty cell in that box, that cell is a 5. Repeat for all nine boxes, then move to the next digit.

3. 3

   Look for naked singles

   A naked single is a cell where only one digit is possible after checking its row, column, and box constraints. If 8 of the 9 digits are already represented across those three groups, the ninth digit is the answer. Fill it with confidence.

4. 4

   Use pencil marks when unsure

   Tap the ✏️ icon (or press N on desktop) to switch to notes mode. In notes mode, tapping a digit writes a small candidate number inside the cell without committing to it. As you solve other cells, candidates automatically become ineligible — your list shrinks until one remains.

5. 5

   Re-scan after every placement

   Each digit you place removes a candidate from up to 20 other cells. Always re-check the row, column, and box of your latest placement — a new naked single or obvious move may have just appeared. The puzzle accelerates as it fills in.

Suppose a row contains the givens: 1, 4, 5, 6, 8. Three cells are empty and the missing digits are 2, 3, 7. Now check the columns those empty cells belong to:

• Empty cell in column 2: column 2 already has a 3 and a 7 → the only candidate is 2. Fill it.
• Empty cell in column 6: column 6 already has a 2 → candidates are 3 or 7. Not yet determined.
• Empty cell in column 9: column 9 already has a 2 and a 3 → the only candidate is 7. Fill it.

Now the row has 1, 2, 4, 5, 6, 7, 8 — and column 6's empty cell must be 3 (the only digit left for the row). Three moves triggered by a column check on one cell.

Think of pencil marks as a working memory aid. When a cell has, say, 4 candidates and you cannot determine which is correct yet, write all four. As you solve other cells in the same row, column, or box, cross off candidates that are no longer valid.

Pencil marks shine in two situations:

• Medium and harder puzzles where naked singles are rare and you need to track multiple possibilities at once.
• When you feel stuck — writing out all candidates often reveals a naked single you missed visually.

On easy puzzles, you may rarely need pencil marks at all. On expert puzzles, they are essential — the whole solution strategy depends on tracking which candidates remain in each cell and spotting patterns across multiple cells simultaneously.

Guessing. Every Sudoku puzzle with a valid solution can be solved by pure logic — no guessing required. If you feel you need to guess, slow down. You are missing a constraint. Guessing wrong creates a chain of errors that can propagate dozens of cells before you notice. Use the undo button, not trial-and-error.

Forgetting the box constraint. New players tend to check only rows and columns. The 3×3 box is an equally powerful constraint. Always verify all three groups before concluding a cell has multiple candidates.

Not re-checking after placements. Every number you enter changes the board. The row, column, and box it touches may now have a naked single or a last-remaining-cell that did not exist a moment ago. Re-scan after every move.

Writing pencil marks incorrectly. If you forget to remove a candidate after placing a digit elsewhere, your pencil marks become misleading. Update candidate lists immediately after each placement, or use the game's notes mode which does this automatically.

Going too fast. One wrong placement early in the puzzle can create a cascade of forced errors that makes the puzzle unsolvable without starting over. Accuracy beats speed, especially while learning.

Given (clue)

A pre-filled cell in the starting puzzle. Givens cannot be changed.

Candidate

A digit that is still legally possible for an empty cell, based on current row, column, and box constraints.

Naked single

A cell with exactly one remaining candidate — the safest and most common beginner deduction.

Hidden single

A digit that can go in only one cell within a row, column, or box, even though that cell has multiple candidates. The digit is "hidden" among others.

Cross-hatching

Scanning rows and columns for a single digit to determine where it can go in each 3×3 box. A fundamental technique for easy and medium puzzles.

Pencil marks (notes)

Small candidate numbers written inside a cell as a memory aid. Essential for medium and harder difficulty.

Naked pair

Two cells in the same group that both contain exactly the same two candidates. Those two values can be removed from all other cells in the group.

Pointing pair

When a candidate in a 3×3 box is restricted to cells that all lie in one row or column, allowing elimination outside the box.

Sudoku Rise offers four difficulty levels, and each one is genuinely different — not just in how many clues are given, but in which techniques you need:

• Easy (38+ clues): Cross-hatching and naked singles are sufficient. Pencil marks are rarely needed. Ideal for learning the constraint system.
• Medium (30–37 clues): Hidden singles and locked candidates become necessary. Pencil marks are strongly recommended.
• Hard (25–29 clues): Naked and hidden pairs and triples are required. Singles alone will not get you far. Accurate candidate tracking is critical.
• Expert (20–24 clues): Advanced techniques — X-Wing, XY-Wing, Swordfish, unique rectangles — become necessary. These puzzles can take 30–60 minutes even for experienced solvers.

Start at Easy and move up only when Easy feels completely comfortable. Jumping to Hard without mastering the easy techniques creates frustration, not learning.

You now know the rule, the grid structure, the core techniques, and the terminology. The best way to learn Sudoku is to play — start with Easy and trust the logic. Work your way up through the Easy, Medium, Hard, and Expert technique guides as you grow more comfortable with each level.