Home › Fun & Games › Sudoku Solver
Sudoku Solver
Type or paste the numbers from your puzzle and press Solve for the full answer in milliseconds. Prefer to solve it yourself? Ask for the next step and the solver explains which technique finds it.
Solving steps
Advertisement
Advertisement
How to use the Sudoku Solver
- Enter the puzzle: click a cell and type its number. Use the arrow keys to move and Backspace to clear. Or paste an 81-character line (use 0 or . for blanks) and press Load.
- Press Solve to fill in the complete solution. Your clues stay black; solved digits appear in blue.
- Want only a nudge? Press Hint: the solver highlights one cell and explains why its number is forced. Press Apply hint to place it.
- Check uniqueness to see whether the puzzle has exactly one solution, none, or several.
- Show all steps lists the whole logical solving path, and Show candidates adds pencil marks to every empty cell.
Sudoku solving techniques used by the hints
The hint button works the way a person solves on paper: it lists the candidates (digits still possible) for every empty cell, then looks for the simplest technique that places a digit. Cells are named by row and column, so R3C5 is row 3, column 5. Boxes are numbered 1–9 from top left to bottom right.
| Technique | What it means |
|---|---|
| Naked single | A cell has only one candidate left because the other eight digits already appear in its row, column or box. |
| Hidden single | Within a row, column or box, a digit fits in only one cell, even if that cell has other candidates. |
| Pointing | Inside a box, all candidates for a digit lie in one row or column. That digit can be removed from the rest of that row or column outside the box. |
| Claiming (box/line reduction) | Inside a row or column, all candidates for a digit lie in one box. That digit can be removed from the other cells of the box. |
| Naked pair / triple | Two cells in a unit share the same two candidates (or three cells share three). Those digits must go in those cells, so they are removed from the other cells of the unit. |
| Advanced | When none of the above helps, the puzzle needs harder techniques such as X-Wing, Swordfish or chains. The hint then reveals the correct digit for the cell with the fewest candidates. |
How to enter a puzzle quickly
- Type row by row: click the top-left cell, type a digit or press Space/0 for an empty cell, then use the right arrow. The arrows wrap at the edges.
- Paste a line: many puzzle sites and books use an 81-character format such as
53..7....6..195.... Paste it into the box and press Load puzzle, or paste straight onto the grid. - Share a puzzle: add
?p=followed by the 81 characters to this page's address to open it with that puzzle loaded. - Double-check clues: if the solver reports no solution, a single mistyped digit is the usual cause. The red highlight only catches duplicates in the same row, column or box.
Mathematically, a valid Sudoku needs at least 17 clues to have a unique solution; this was proved by an exhaustive computer search in 2012. Most newspaper puzzles give between 22 and 36 clues.
Frequently asked questions
How does the Sudoku solver work?
It uses backtracking search with bitmask candidate tracking: it always fills the empty cell with the fewest possible digits first, and backs up when a choice leads to a contradiction. This finds the solution of any valid 9×9 puzzle, even the hardest ones, in a few milliseconds.
What techniques do the hints use?
Hints look for naked singles, hidden singles, locked candidates (pointing and claiming) and naked pairs and triples, the same techniques people use on paper. If a puzzle needs something more advanced, the hint takes the next digit from the computed solution and says so.
What does it mean if a Sudoku has more than one solution?
A proper Sudoku has exactly one solution. If the uniqueness check finds two or more, a clue is missing or was entered wrongly, and you can't solve it by logic alone. Puzzles with fewer than 17 clues never have a unique solution.
Why does it say my puzzle has no solution?
Either two equal digits share a row, column or 3×3 box (these are highlighted in red), or the clues are consistent at first glance but contradict each other deeper down. Compare your entries with the printed puzzle; a single mistyped digit is the usual cause.
Can I paste a puzzle?
Yes. Paste 81 characters, reading left to right and top to bottom, using digits 1–9 for clues and 0, a dot or a dash for empty cells. Spaces, line breaks and grid characters like | and + are ignored.
Is the solver free and private?
Yes. It is free with no sign-up and runs entirely in your browser; your puzzle is never sent anywhere.
Related tools
Sudoku OnlinePlay free Sudoku with 4 difficulty levels, notes, hints and a timer.Maze GeneratorCreate random mazes in any size, solve them with the arrow keys, then print or save as PNG.MinesweeperPlay classic Minesweeper: 3 difficulties, flags, timer and a safe first click.Word UnscramblerUnscramble letters into every possible word, with blank tiles, length filters and Scrabble scores.SolitairePlay classic Klondike Solitaire with Draw 1 or Draw 3 and undo.Spider SolitairePlay Spider Solitaire online with 1, 2 or 4 suits, hints, unlimited undo and a timer.Play Chess vs ComputerPlay chess online against the computer at 8 difficulty levels.Connect FourPlay Connect 4 online against the computer or a friend.Snake GamePlay classic Snake online with speeds, wall modes and high scores.Tic Tac ToePlay tic tac toe against an unbeatable AI or a friend.Block Puzzle GameClassic falling blocks puzzle game with levels and high score.2048 GamePlay 2048 online with swipe controls, undo and best score.Coin FlipFlip a coin online: heads or tails, multiple coins and stats.Yes or No WheelSpin the wheel for a yes or no answer to any question.Random Name GeneratorGenerate random first and last names by gender and origin.Random Team GeneratorSplit a list of names into random, balanced teams.Zodiac Sign CalculatorFind your zodiac sign, element and best matches from your birthday.Zodiac CompatibilityCheck love compatibility between two zodiac signs.Love CalculatorEnter two names and get a fun love compatibility score.Dice RollerRoll a D6 or any RPG dice (D4 to D100) with totals and history.Random Number GeneratorPick random numbers in any range, unique or lottery-style.Random Letter GeneratorPick random letters from the alphabet, with vowel, case and no-repeat options.Random Country GeneratorPick random countries with flags, capitals, population and area.Random Date GeneratorGenerate random dates between two dates, with weekday and format options.Numerology CalculatorFind your life path, expression and soul urge numbers from name and birthday.Birth Flower & Birthstone FinderLook up the birthstones and birth flowers for any month, with meanings.Picker WheelSpin a wheel to pick a random name or choice.Random Dog PicturesRandom dog photos and fun dog facts.Random Cat PicturesRandom cat photos and fun cat facts.Random Parrot PicturesRandom parrot photos and bird trivia.Dog Web StumbleJump to a random dog website.Cat Web StumbleJump to a random cat website.Parrot Web StumbleJump to a random parrot website.Random Animal GeneratorGet a random animal with its class, habitat and a fun fact, with filters.Word Guess GameGuess the hidden five-letter word in six tries. Unlimited games, stats and hard mode.Rising Sign CalculatorFind your ascendant sign and degree from birth date, time and place.Random Movie PickerCan't decide what to watch? Pick a random film by genre, decade and runtime.HangmanClassic friendly hangman word game with categories, hints and difficulty levels.Tarot Card ReadingDraw a free tarot spread from a full 78-card deck with upright and reversed meanings.Random Food PickerCan't decide what to eat? Spin a cuisine wheel and get a dish that fits your diet.Memory Card GameFlip cards and match emoji pairs on 4×3 to 6×6 grids, with moves, timer and best scores.Fortune Cookie GeneratorCrack a virtual fortune cookie for an original fortune, lucky numbers and a daily pick.Truth or Dare GeneratorDraw clean truth or dare questions for family, teens or parties, with player turns.Flappy GameTap to flap a round chick through bamboo gaps and beat your high score.Baby Name GeneratorDiscover 1,700+ baby names filtered by gender, origin and letter, and save favorites.Would You Rather QuestionsRandom would you rather dilemmas in five categories. Vote and see your A/B split.Dino Runner GameJump cacti and duck buzzing beetles in an original endless desert runner.Pet Name GeneratorFind the perfect name for a dog, cat, bird or bunny by species, style and coat color.Never Have I Ever QuestionsClean and party never have I ever questions with a built-in point counter for players.Typing GameType the falling words before they land; level up and track your WPM and accuracy.Fantasy Name GeneratorCreate elf, dwarf, orc, dragon and other fantasy names from race-specific syllable rules.Chinese Zodiac CalculatorFind your Chinese zodiac animal, element and yin or yang from your exact birth date.Random Question GeneratorRandom conversation starters: icebreakers, deep, funny, work-friendly and kids questions.Math Quiz GameTimed mental math rounds with four operations, five levels, streaks and high scores.Username GeneratorGenerate cool usernames and gamertags by style, fitted to each platform's rules.Magic 8 BallAsk a yes-or-no question, shake the ball and get one of the 20 classic answers.Flag QuizGuess the flags of all 196 countries in four modes, from multiple choice to timed.Band Name GeneratorInvent band names for 14 music genres, or blend two genres, with album titles too.Writing Prompt GeneratorRandom story starters, first lines, characters, settings, twists and poem prompts in 11 genres.Map QuizFind countries on a clickable world map or name the highlighted one, by continent.Drag Name GeneratorFind your drag queen or drag king name: puns built from your own name in seven styles.Fantasy Creature GeneratorInvent original fantasy creatures with a name, body, powers, habits, weakness and danger level.Periodic Table QuizLearn all 118 elements: quiz symbols, names and atomic numbers or click them on the table.Rapper Name GeneratorTurn your name into a rap name in seven styles, from Lil and MC to trap, drill and emo rap.Lottery Number GeneratorSecure random quick picks for Powerball, Mega Millions, EuroMillions, Lotto and custom games.Spelling Bee GameMake words from 7 honeycomb letters, always using the center letter. New daily puzzle.Superhero Name GeneratorInvent original superhero names with powers, an origin story and a weakness.Secret Santa GeneratorDraw Secret Santa names with exclusions and send everyone a private reveal link, no sign-up.Jigsaw PuzzleTurn a sample picture or your own photo into a 12 to 150 piece jigsaw puzzle and solve it.Pirate Name GeneratorGet swashbuckling pirate names from your first name, plus ship names, in four styles.Raffle DrawPaste names, add extra tickets and draw one or many random raffle winners with confetti.Sliding PuzzlePlay the 15 puzzle and 3×3 to 6×6 sliding tile puzzles with numbers or your own photo.Couple Name GeneratorBlend two names into ranked ship names and couple names, from Brangelina-style to overlaps.Random Card DrawShuffle a 52-card deck and draw one or more random playing cards, with jokers and history.Mahjong SolitaireMatch pairs of free tiles to clear the Turtle and two smaller layouts, with hints, shuffle and undo.Age on Other PlanetsSee how old you are on Mars, Jupiter and every other planet, plus your next birthdays.Anagram SolverFind every anagram of a word or phrase: single words, multi-word anagrams and all sub-words.Scrabble Word FinderFind the highest-scoring words from your rack, with blank tiles, patterns and bingo bonus.Wordle SolverEnter your guesses and colours to see every possible answer and the best next guess.Crossword SolverFind words that fit a crossword pattern like c?t from the length and the letters you know.Word Search GeneratorMake a word search puzzle from your words, play it online or print it with an answer key.Pong GamePlay classic Pong online against the computer on 3 levels or with a friend, first to 11.Breakout GameClassic brick breaker game with levels, power-ups and lives. Play with mouse, touch or keyboard.Whack-a-MoleWhack the moles before they hide in 30 or 60 second rounds. Speed increases, best score saved.Simon Says GameRepeat the growing color and sound sequence. Classic memory game with strict mode and high score.Rock Paper ScissorsPlay rock paper scissors vs the computer in best-of matches, with stats and a lizard-Spock mode.CheckersPlay checkers online against the computer or a friend, with kings, undo and hints.ReversiPlay Reversi (Othello rules) online vs a 3-level computer or a friend, with move hints.GomokuGet five in a row on a 15×15 board against a smart computer or a friend.Battleship GamePlace your fleet and sink the computer's ships in this classic naval guessing game.FreeCellPlay FreeCell solitaire online with the classic numbered deals, undo, hints and auto-move.Mastermind GameCrack the secret 4-color code in 10 tries using black and white feedback pegs.Tower of HanoiPlay the Tower of Hanoi puzzle with 3 to 8 disks, or watch it solve itself in the fewest moves.Bingo Card GeneratorMake printable 75-ball or custom word bingo cards, from 1 to 200 unique cards, as PDF or print.Bingo Number GeneratorFree bingo caller for 75 or 90 balls with a live board, auto-call timer and spoken numbers.Online ScoreboardKeep score for any game: big team scores, game clock, periods, fullscreen and sport presets.Tournament Bracket GeneratorMake single or double elimination brackets for 2-64 players, click winners to advance, print.Trivia Quiz300+ general knowledge trivia questions in 10 categories. 10-question rounds with a timer and score.Random Fact GeneratorGet random fun facts about animals, space, the body, history, science, food and more.Random Joke Generator200+ clean, family-friendly jokes: dad jokes, puns, knock-knock jokes and more. Tap to reveal.Random Riddle Generator150+ riddles with hidden answers in easy, hard and kids levels. Guess, get a hint or reveal.Team Name GeneratorGenerate catchy team names for sports, work, trivia nights and gaming, with your own keyword.Business Name GeneratorTurn a keyword and industry into brandable business name ideas, with a .com check link.Charades GeneratorRandom charades words by category and difficulty, with a round timer, team scores and kids mode.