Sudoku
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Guide

How to Play Sudoku

Sudoku is a 9×9 logic puzzle. Fill every row, column, and 3×3 box with the digits 1–9, using scanning, pencil marks, and pattern spotting — no arithmetic and no guessing.

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The objective

Fill the grid. One of each digit, everywhere.

A Sudoku is a 9×9 grid divided into nine 3×3 boxes. Some cells start with digits — the givens. Your job is to fill the rest so that every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once, with no repeats.

There is no arithmetic and no timer pressure. Every proper Sudoku has exactly one solution, and it can always be reached by logic alone: at any point in a solvable grid, there is a digit that must be true somewhere.

The game is free, runs in the browser, and needs no account. Open play Sudoku when you want the board; use this guide for the rules, the difficulty levels, and the techniques that finish a hard puzzle.

Controls

Click, type, or tap

Select a cell, then enter a digit. Everything else — notes, undo, hints, pause — has a keyboard shortcut on desktop and a button on the tool row for touch.

  • Desktop

    Click + number keys

    Click a cell to select it, then press 1–9 to enter a digit. Press the same digit again, 0, Backspace, or Delete to clear it. Arrow keys move the selection around the grid.

  • Keyboard shortcuts

    Notes, undo, hint

    Press N or the space bar to toggle pencil-mark mode, U or Ctrl+Z to undo, H for a hint, P to pause, and M to mute. Notes mode enters small candidate digits instead of a final answer.

  • Phone & tablet

    Tap + on-screen pad

    Tap a cell, then tap a number on the pad below the board. The tool row gives you Undo, Erase, a Notes toggle, and Hint without a keyboard. The whole layout fits above the fold in portrait.

The loop

Four steps, repeated until it is solved

Every Sudoku is the same loop: read the grid, find a digit that is forced, place it, repeat. Getting good is getting faster at spotting the forced digit.

  1. 1

    Read the grid

    A Sudoku is a 9×9 grid split into nine 3×3 boxes. Some cells already hold digits — the givens. The rest are yours to fill.

  2. 2

    One of each, everywhere

    Every row, every column, and every 3×3 box must contain the digits 1 to 9 exactly once. No digit may repeat in any row, column, or box.

  3. 3

    Place what must be true

    Look for a cell where only one digit can legally go, or a digit that fits only one cell in a row, column, or box. Enter it and move on.

  4. 4

    Finish with no repeats

    Keep going until all 81 cells are filled. There is exactly one valid solution, so a correct grid is the finished puzzle.

Rules & scoring

How this Sudoku is actually scored

The rules never change between levels. A timer runs while you play, three wrong digits end the game, and notes, hints, and undo are always available.

  • The objective

    Fill the 9×9 grid so that every row, every column, and every 3×3 box contains each digit from 1 to 9 exactly once. The givens can never be changed, and there is always exactly one solution.

  • Mistakes

    Entering a digit that does not match the unique solution is a mistake. The cell turns red and the mistake counter climbs. Three mistakes ends the game — a light guardrail that keeps every puzzle honest without a real penalty for stopping to think.

  • Notes

    Pencil-mark mode lets you write small candidate digits into a cell. Placing a confirmed digit automatically clears that candidate from every cell in the same row, column, and box, so your notes stay tidy.

  • Hints and undo

    A hint reveals the correct digit for the selected empty cell and locks it. Undo steps back through your entries and note changes one at a time. Neither counts against you beyond the on-screen tally.

Use New game from the in-game footer to start a fresh puzzle at any time. Details on local saves and resets live in the Sudoku FAQ.

Difficulty

Easy, Medium, Hard, and Expert

Difficulty is a generation setting, not a different game. The 9×9 grid and the rules are identical at every level — only the number of givens and the solving techniques required change.

  1. 01 · ~40 givens

    Easy

    Around 40 given numbers. Every cell can be solved by simple scanning — a relaxed warm-up.

  2. 02 · ~32 givens

    Medium

    Around 32 givens. Expect to lean on pencil marks and spot the odd hidden single.

  3. 03 · ~27 givens

    Hard

    Around 27 givens. Naked and hidden pairs come into play; careful notes pay off.

  4. 04 · ~24 givens

    Expert

    Around 24 givens. A genuine challenge that rewards pointing pairs, box/line reduction, and patience.

Common mistakes

Why a grid stalls

Most Sudoku errors are process errors, not bad luck. These are the habits that end a promising grid early.

  • Filling cells out of order

    Jumping to an interesting-looking empty cell before the easy forced digits are in wastes moves. Clear every naked and hidden single first — they cascade, and the puzzle often opens up on its own.

  • Ignoring pencil marks on harder boards

    On Hard and Expert puzzles, trying to hold every candidate in your head leads to mistakes. Pencil in candidates for a whole box or row and let the pairs and triples reveal themselves.

  • Guessing when stuck

    A single guess can send you deep into an unsolvable branch that only shows itself moves later. Every valid Sudoku has a logical next step; if you cannot see it, re-scan the most-placed digits.

  • Forgetting to prune candidates

    After placing a digit, remove it from the notes of its row, column, and box. Stale candidates are the most common reason a "naked single" gets missed.

Strategy habits

Tips to solve faster

Treat these as habits, not shortcuts. For a technique-by-technique walkthrough, see the full tips page.

  • Scan rows, columns, and boxes for a digit that already appears three or four times — it is often forced into one remaining cell.
  • Turn on notes and pencil in every candidate for a cell. A cell with a single candidate is a "naked single" you can place immediately.
  • A digit that can only go in one cell of a box, row, or line is a "hidden single", even if that cell has several candidates.
  • When two cells in a unit share the same two candidates, those digits are locked to that pair — erase them from the rest of the unit.
  • If a box’s candidates for a digit all sit in one row or column, that digit cannot appear elsewhere in that row or column (pointing pair).
  • Fill the boxes and rows with the most givens first; each digit you place removes candidates elsewhere and unlocks the next step.
  • Never guess. Every solvable position has a logical next move — if you cannot find one, look again at the digits you have placed most.

Where you can play

Same puzzle on phone and desktop

sudokupuzzles.games runs in any modern browser with no app to install. Your current puzzle and stats stay in the browser you played in.

  • Desktop browsers

    Chrome, Edge, Firefox, and Safari all run sudokupuzzles.games with no plugin. Use the mouse to select and the number row to fill; keyboard shortcuts cover notes, undo, hints, and pause.

  • Phones and tablets

    The board and number pad are touch-first and sized to fit a portrait screen without scrolling. Tap a cell, tap a digit, and use the tool row for notes, erase, undo, and hints.

  • Progress on this device

    Your current puzzle, best times, win counts, and streaks per difficulty live in local browser storage. Close the tab and your game is waiting when you come back — on that device and browser only.

Still stuck on a rule? Read the Sudoku FAQ, see who makes sudokupuzzles.games, or jump in and play.

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