Classic Sudoku 9X9
blackplotan
Please rotate your device
How it's different
Classic Sudoku 9x9 is the original format, and the one every other puzzle on zagzook builds from. Fill the 9x9 grid so every row, every column, and every 3x3 box contains the numbers 1 through 9 exactly once - no repeats, no shortcuts. It's the same set of rules whether you're playing with numbers, letters, icons, or colors from the picker above; only the symbols change, never the logic. If you're new to Sudoku, this is the board to learn on before trying the variants (Sudoku X adds diagonals, Hyper adds extra regions, and 6x6/8x8 shrink or stretch the grid itself).
How to play
Use your keyboard or the number buttons to fill in the blanks. There are three modes for entering numbers:
Cell First mode: click the cell you want to fill in first, then select the number you want to enter.
Number First mode: select the number you want to enter first, then click the cell you want to fill it into.
Memo mode: this button lets you pencil in a memo of candidate numbers in a blank cell, instead of committing to one right away.
- Made a mistake? Undo steps back through your moves.
- Stuck? The hint button reveals one correct cell for you.
- Pick your difficulty (Easy, Medium, Hard, Very Hard) from the tabs above - each one is a genuinely different puzzle, not the same board made easier.
- Solve the board completely and it submits automatically - no button to press, no confirmation needed.
Rules
Fill in the blanks with numbers from 1 to 9. Each row, column, or 3x3 block must contain the numbers 1 through 9 exactly once.
Strategy tips
- Start with the fullest rows, columns, and boxes. Fewer empty cells means fewer possibilities to check, so you'll find sure answers faster there than on a nearly-empty box.
- Look for cells with only one option left. If a cell's row, column, and box already rule out every number except one, that's your answer - no guessing required.
- Turn on notes once scanning alone stalls. Pencil in every candidate for the cells you're unsure about; patterns become much easier to spot once they're written down.
- Watch for a number confined to one row or column within a box. If a number can only go in one row of a box, it can be ruled out from that same row in every other box.
FAQ
Is there only one solution to each puzzle?
Yes. Every puzzle on zagzook is generated with exactly one valid solution - no guessing between multiple right answers.
Can I play the same difficulty more than once in a day?
You can, just for fun - but only your first correct solve of the day counts toward today's leaderboard. Once you've completed a difficulty, that tab locks for the rest of the day.
When does a new puzzle appear?
Every day at midnight UTC, across every difficulty. It's the same puzzle for everyone playing that day, wherever you are.
Do Easy, Medium, Hard, and Very Hard use the same board?
No - each difficulty is a genuinely different puzzle with its own solution, not the same board with numbers hidden or revealed to fake an easier version.
Does switching between numbers, letters, icons, and colors change the puzzle?
No. It's purely how the values are displayed - the logic underneath stays exactly the same no matter which symbol style you pick.