What Is This?
Sudoku is a logic puzzle played on a 9x9 grid split into nine smaller 3x3 boxes. Every row, column, and 3x3 box must end up containing each number from 1 to 9 exactly once. The puzzle starts with some cells already filled in, and your job is to fill the rest using deduction rather than guesswork. A well-formed sudoku always has exactly one solution, and that solution can always be reached through logic alone, which is what makes the game satisfying: every move you make can be justified by what is already on the board. This browser version offers three difficulty levels. Easy puzzles open with plenty of clues and fall into place quickly, medium puzzles balance the starting clues so you have to work a little, and hard puzzles give you few clues, so you have to hold candidate numbers in your head or jot them as notes. There is no account, no download, and the timer is optional, so you can solve at your own pace and compare runs whenever you want.
How to Play
- Pick Easy, Medium, or Hard to start a puzzle.
- Tap a cell and choose a number from 1 to 9.
- The number is accepted only if it does not already appear in that row, column, or 3x3 box.
- If a cell has several possible numbers, add them as notes and cross them out as the grid fills in.
- Keep going until every empty cell is filled and the whole grid is complete.
- Use Restart to clear your entries and try the same puzzle again, or start a fresh one.
- Watch the timer if you want to compare your solving speed across puzzles.
How the Score Is Calculated
Your result on this sudoku is the completed grid, with the timer recording how long the solve took. There is no point system, because finishing the puzzle is the win. A clean solve with no wrong entries is a better result than a rushed one, because every wrong number has to be found and undone, and that costs more time than it saves. The best time on your device is saved, so you can chase it on the next puzzle. If you solve the same difficulty several days in a row, the trend in your times tells you more than any single run, since a slow solve after a long day says nothing about your skill. When you move up to Medium or Hard, expect slower first solves; the point of the difficulty levels is to stretch your reading of the grid, not to hand you a fast time.
Tips to Improve
- Start with the row, column, or 3x3 box that already has the most numbers filled in; it has the fewest empty cells to resolve.
- Before anything clever, scan for cells where only one number can fit, and fill those immediately.
- Treat each 3x3 box as a unit. Many beginners solve rows and columns but forget that box logic locks numbers in first.
- Use notes for cells with two or three candidates, and cross candidates off as numbers settle elsewhere in the same unit.
- If a number can only go in one row or column of a box, that number is locked there, which rules it out of the rest of the box.
- When you are stuck, pick the unit with the fewest empty cells and work it cell by cell; the answer is usually in the tightest spot.
- Read the board from a different corner if your scan has gone stale. A fresh starting point reveals candidates you stopped seeing.
- Take a short break when the grid stops talking. Sudoku is a reading game, and a rested read of the board beats staring at the same three cells.
Common Mistakes
The most common mistake is guessing. Because every puzzle here is solvable by logic, a guessed number that happens to be wrong sends you down a chain of contradictions, and undoing a wrong guess takes longer than the correct move took. The second mistake is ignoring the 3x3 boxes and solving only by rows and columns; most beginner logic lives in the boxes. The third is entering a number that is fine in its row but repeats in its column or box. Always check all three units before committing a digit. A fourth mistake is refusing to use notes, which forces your short-term memory to hold too many candidates and leads to avoidable errors. Notes are a normal part of the game at Medium and Hard, not a sign of weakness.