Sudoku FAQ

Sudoku is a single-player logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. Some cells start filled with digits called givens. Your job is to fill every remaining cell so that each row, each column, and each 3×3 box contains the digits 1 through 9 exactly once. No arithmetic is involved — it is pure deduction. The modern puzzle was popularised in Japan in the 1980s under the name Sudoku ("single number") and became a worldwide fixture after 2004.

Yes. sudokupuzzles.games is completely free and runs entirely in your browser. There is nothing to buy, download, or install, no account, and no ads interrupting a puzzle. Open the page and a board is ready.

No. sudokupuzzles.games is a 100% browser-based game built with HTML and JavaScript. It runs in Chrome, Edge, Firefox, Safari, and other modern browsers on desktop and mobile without a plugin, app store listing, or installer.

The earliest version, "Number Place", appeared in a US puzzle magazine in 1979, designed by Howard Garns. It was picked up by the Japanese publisher Nikoli in 1984 and renamed Sudoku. A New Zealand puzzle enthusiast, Wayne Gould, built a program to generate puzzles and placed them in The Times of London in 2004, which triggered the global boom. The rules have not changed since.

Select an empty cell and enter the digit that must go there. A digit is correct when it does not already appear in that cell’s row, its column, or its 3×3 box. Work through the grid placing forced digits — cells where only one digit fits, or digits that fit only one cell in a unit — until all 81 cells are filled. There is exactly one valid completion.

A proper Sudoku has exactly one solution, and every puzzle on this site is checked for that before it is served. That is what makes the puzzle solvable by logic alone: you never have to guess, because at any point there is a digit that must be true.

Entering a digit that does not match the unique solution counts as a mistake; the cell turns red and the counter goes up. Three mistakes ends that game. It is a light guardrail rather than a harsh penalty — you can start a new puzzle instantly, and taking your time to think never costs anything.

Notes mode lets you write small candidate digits into a cell instead of a final answer — the same thing players do with a pencil on paper. When you later place a confirmed digit, that candidate is automatically erased from every cell in the same row, column, and box so your notes stay accurate.

A hint fills the selected empty cell with its correct digit and locks it, the same as a given. If no cell is selected, the hint reveals the next unsolved cell. Hints are tracked on screen but carry no penalty beyond that tally.

No. The digits 1–9 are just nine distinct symbols; you could play with nine colours or letters instead. Sudoku is entirely about logical constraints — where a symbol can and cannot go — not arithmetic.

That game ends, but a new puzzle is one click away and your difficulty and settings carry over. You can also restart the same puzzle from scratch, or lower the difficulty if a level is consistently ending early.

When all 81 cells match the solution, the puzzle is done: the timer stops, a completion panel shows your time and mistakes, and your stats for that difficulty update — best time, games won, and current streak. From there you can start another puzzle at the same or a different level.

Difficulty is set by how many digits the puzzle starts with and which solving techniques are needed to finish it. Easy boards (around 40 givens) fall to simple scanning. Medium needs pencil marks and hidden singles. Hard brings in naked and hidden pairs. Expert (around 24 givens) rewards pointing pairs, box/line reduction, and patience. The rules and the 9×9 grid never change between levels.

Learn to spot naked singles (a cell with one candidate) and hidden singles (a digit with one home in a unit) quickly, then add naked pairs and pointing pairs. Use notes on anything above Easy. Practising the same difficulty repeatedly trains pattern recognition faster than jumping straight to Expert. Our tips page walks through each technique.

A naked single is an empty cell where, after eliminating every digit that appears in its row, column, or box, only one candidate remains. A hidden single is a digit that can legally go in only one cell of a particular row, column, or box, even though that cell may still have other candidates. Both let you place a digit with certainty; hidden singles are just harder to see.

X-wing is an elimination pattern. If a digit’s candidates in two different rows are confined to the same two columns, then that digit must occupy one cell in each of those rows within those columns — so it can be removed as a candidate from the rest of both columns. The same works with rows and columns swapped. It is an Expert-level tool for breaking a stuck grid.

On Easy puzzles you often will not need them. From Medium upward, pencil marks are the difference between steady progress and repeated mistakes — they turn "I think a 4 goes here" into a visible fact you can act on. Placing a confirmed digit prunes candidates for you automatically.

Yes. Your current in-progress puzzle is saved in your browser, so closing the tab and returning later picks up where you left off. Best times, games won, and streaks are also stored per difficulty. Nothing is sent to a server, and there is no login, so a different device or browser starts fresh.

Yes. The layout is built for phones and tablets: the board and number pad fit a portrait screen without scrolling, and a tool row covers notes, erase, undo, and hints. Tap a cell, then tap a digit.

The page needs a connection to load the first time. After that some browsers keep the tab usable without a network, since all puzzle generation and solving happen on your device. There is no dedicated offline app.

Local saves are cleared if you clear cookies or site data for sudokupuzzles.games, switch browsers or devices, or use a private window that has since closed. Some privacy tools and "lite" browser modes also wipe local storage. Because the save never leaves your browser, it cannot be recovered from our side.

No. There is no sign-up, no email, and no profile. Your puzzle, best times, and streaks stay in this browser on this device. The trade-off is that we cannot restore your history on a new device.

Any current browser with JavaScript enabled: Chrome, Edge, Firefox, and Safari on desktop, plus their mobile versions. If the board does not respond, update the browser, allow scripts for this site, and reload.