How to play sudoku

Sudoku is a logic puzzle played on a 9×9 grid. The goal is to fill every row, column, and 3×3 box with the numbers 1 through 9, each used exactly once. This guide walks you through the rules, the core techniques, and how to keep improving, from your first puzzle to your hundredth.

Scanned this from a Mindful Sudoku book? Skip to hints by puzzle number.

Choose your path:

• New to sudoku? Start at the top.
• Already know the rules? Jump to Scanning.
• Stuck on a puzzle from your book? Find hints by puzzle number.

What is sudoku?

Sudoku is a logic-based number puzzle played on a 9×9 grid. The grid has three kinds of regions: nine rows, nine columns, and nine 3×3 boxes (also called blocks, or as we like to call them, mini grids). When we say "region," we mean any one of those three.

The rules are simple:

• Every row must contain the numbers 1 through 9, each used exactly once
• Every column must contain the numbers 1 through 9, each used exactly once
• Every 3×3 box must contain the numbers 1 through 9, each used exactly once

Each puzzle begins with some numbers already filled in. These are called the givens. Your job is to use logic to figure out where every other number belongs.

Two cells see each other when they share a row, column, or box. Cells that see each other can't hold the same number.

A candidate is any number that could still legally go in a cell. As you solve, you narrow each cell's candidates down until only one remains.

A well-constructed sudoku has exactly one solution, reachable through logic alone. If you're stuck, there's always a next step to find.

Notation

Throughout this guide, we use row-column notation to refer to specific cells: r for row, c for column. r7c2 means row 7, column 2. r3c7 means row 3, column 7. It's the standard used across the online sudoku community.

You may also see letter-number notation in print books, including ours. B7 means column B, row 7. Both systems describe the same cell. Use whichever feels natural.

Scanning

The first technique every solver learns is scanning. Scanning means looking across a row or down a column to check which numbers are already placed, and which are still missing.

Start by picking a single number, say, the 9s. Scan the entire grid to see where 9s already appear. Notice which rows, columns, and boxes still need a 9. This alone helps you spot cells where a number has nowhere else to go.

Scanning works two ways. Cell-first asks: what number fits in this cell? You look at one empty cell and check what its row, column, and box already contain. Digit-first asks the reverse: where does this number go in this region? You pick a number and search the region for its only possible home. Same scan, opposite question. You'll use both throughout solving.

Scanning is the foundation of every technique that follows. Most beginners spend 70% of their solving time here, which is exactly right.

Crosshatching

Crosshatching is the most-used scanning technique in sudoku. It combines row and column scans to narrow down where a specific number must go inside a 3×3 box.

The method:

1. Pick a box and a number you want to place in it.
2. Scan each row that passes through the box. If any row already contains that number, eliminate the box cells in that row.
3. Scan each column that passes through the box. Same elimination.
4. Whatever cells remain are your candidates. If only one remains, that's your answer.

Worked example

Let's place the 9 in the bottom-left box of this grid.

The bottom-left box already contains 7, 1, and 8. We need to place 2, 3, 4, 5, 6, and 9. Let's focus on the 9.

Scan the three rows passing through the box (rows 7, 8, 9):

• Row 7 has a 9 at r7c6. Eliminate all cells of the box in row 7.
• Row 8 has no 9 yet.
• Row 9 has a 9 at r9c9. Eliminate all cells of the box in row 9.

Scan the three columns passing through the box (columns 1, 2, 3):

• Column 1 has a 9 at r3c1. Eliminate all cells of the box in column 1.
• Column 2 has a 9 at r6c2. Eliminate all cells of the box in column 2.
• Column 3 has no 9 yet.

After those eliminations, only one empty cell remains in the box: r8c3. The 9 must go there.

That's crosshatching. Systematic elimination until only one option survives. Repeat the same process for every missing number, one at a time, across every box.

Singles: naked and hidden

Once you've used scanning and crosshatching, the next techniques are naked singles and hidden singles. Both find a cell where only one number is possible. The logic comes from two different angles.

Naked single. A cell that can only hold one number, because every other number already appears somewhere in its row, column, or box. You usually find naked singles by writing small notes (candidates) in each empty cell. When a cell ends up with only one candidate left, that's a naked single.

Hidden single. The reverse approach. Instead of looking at one cell, you look at an entire row, column, or box and ask: is there a number that can only go in one cell within this unit? For example, if a row needs a 4, and five of its empty cells are blocked from holding a 4 (because their column or box already has one), the 4 must go in the remaining cell, even if that cell has other candidates.

Hidden singles are the most common "breakthrough" move in sudoku. Notice them in rows, columns, and boxes that are already mostly filled.

Pairs: naked and hidden

When scanning and singles stop making progress, pairs are your next tool.

Naked pair. Two cells in the same row, column, or box that both contain the exact same two candidates and nothing else. If two cells must each be either 3 or 7, then no other cell in that unit can be a 3 or 7. You can safely remove 3 and 7 from every other cell's candidates in that shared row, column, or box.

Hidden pair. Two numbers that can only go in two specific cells within a row, column, or box, even if those cells have other candidates. Once you notice a hidden pair, you can strip away all the other candidates from those two cells, because only the two "hidden" numbers can actually live there.

Pairs work by eliminating candidates. Once those candidates are gone, more singles often appear. Applying one technique often creates the conditions for the next.

Beyond the basics

Once you're comfortable with scanning, singles, and pairs, sudoku opens up. Techniques beyond the basics fall into several families:

• Locked candidates: a digit's possible cells in one region are confined to where that region overlaps another. Two flavors: pointing (box → line: a digit's cells in a box lie along one row or column, so eliminate it from the rest of that line outside the box) and claiming (line → box: a digit's cells in a row or column lie inside one box, so eliminate it from the rest of that box). One catch: the technique only works when all of the digit's possible cells lie in the intersection.
• Single-digit patterns: patterns built from where a single digit can go across the grid (Skyscraper, 2-String Kite, Empty Rectangle)
• Fish: patterns across multiple rows and columns (X-Wing, Swordfish, Jellyfish)
• Wings: chained logic across three or more cells, each with two candidates (XY-Wing, XYZ-Wing, W-Wing, WXYZ-Wing)
• Coloring and chains: connecting cells through "if-this-then-that" reasoning across the grid (Simple Coloring, AIC, Forcing Chains)
• Uniqueness-based: using the fact that a valid sudoku has exactly one solution to eliminate candidates that would create a second one (Unique Rectangle, BUG)

A few specific techniques you'll encounter as you progress:

• X-Wing: a fish pattern across two rows and two columns that eliminates candidates along the intersecting lines
• Skyscraper: a single-digit pattern across two columns where the digit has two possible cells in each, with one pair sharing a row and the other pair rising above it
• Swordfish: an extension of the X-Wing, across three rows and three columns
• Jellyfish: the four-fish, extending Swordfish across four rows and four columns. Rare; usually only appears at Expert or higher difficulty.
• XY-Wing (also called Y-Wing): chained logic across three cells, each with two candidates

Advanced techniques look complex at first, but each one is just a pattern. Learn them one at a time. You'll know you're ready for the next when the current one feels familiar.

How difficulty works

Sudoku difficulty is determined by the hardest technique required to solve the puzzle. This is the same standard used by the World Puzzle Federation and the leading sudoku engines. The number of givens is a less reliable indicator. A puzzle with 30 givens can be harder than one with 26, if the 26-given puzzle only needs scanning while the 30-given puzzle requires an X-Wing.

Typical difficulty tiers:

These tier classifications aggregate the conventions used across the online sudoku community. Where sources diverge on which tier a technique belongs to, we follow the consensus among the majority of sources. The principle is consistent everywhere: harder techniques mean harder puzzles.

Every Mindful Sudoku puzzle is classified using this standard. Our books are intentionally skewed to the easier side of the scale. The hardest technique required for each Mindful Sudoku difficulty level is published with each volume, so you always know what to expect.

Tips for new players

Take notes. Small candidate numbers written in the corners of empty cells. (You may also see these called pencil marks or candidates on other sites; we call them notes.) For Very Easy and Easy puzzles, you can usually solve without them. Once you start needing pairs, triples, or any technique beyond singles, notes become essential. Those patterns are only visible when you can see every candidate. A common recommendation: hold off on notes until basic scanning and singles stop yielding new placements. Adding them earlier tends to clutter the grid without revealing anything you couldn't already see. Top solvers use notes on nearly every puzzle harder than Easy. Notes are technique.

Trust the logic. A well-constructed sudoku can always be solved by logic alone. If you find yourself guessing, there's likely a move you haven't noticed yet. Return to the grid and scan again for hidden singles or pairs. Guesses tend to create contradictions down the line that require starting the puzzle over.

Take breaks. Sudoku rewards a clear mind. If you're stuck for more than a few minutes, step away. Coming back with fresh eyes almost always reveals the move you missed.

Start easy. Technique grows through repetition. Solving ten easy puzzles will teach you more than working through a single expert grid.

The Mindful Sudoku Method

At Mindful Sudoku, we treat sudoku as a practice.

We teach a two-step approach we call Play → Reflect. It draws on the long tradition of active-modality mindfulness, like walking meditation or art-making, where presence emerges through engagement.

1. Play. Solve the puzzle. As you work, the mind moves from scattered to focused. The noise softens. Play is the practice itself. The logic of sudoku asks for just enough attention to settle the mind, without creating new stress.

2. Reflect. From that grounded state, turn to a journaling prompt. Insight lands more easily when the noise has settled. This is where the real self-work happens. Just you, present and paying attention.

Every puzzle in our books is paired with a guided reflection prompt designed for exactly this moment.

Keep learning

Three ways to go deeper.

Frequently asked questions