Wiki
19 Puzzle Sudoku: the complete wiki
Classic 9×9 Sudoku: fill the grid so every row, every column and every 3×3 box holds the numbers 1 to 9 with no repeats. There’s no arithmetic involved; it’s pure logic, and every Vexply puzzle has exactly one solution, so it can always be solved by reasoning, never by guessing.
How to play
The four levels aren’t just about how many numbers are given: each puzzle is solved internally with the same techniques a person would use, and graded by the hardest one it needs. So an Easy puzzle will never ask you for an X-Wing, and an Expert one can’t be finished just by spotting obvious cells.
Alongside free play there’s a daily Sudoku: the same puzzle for everyone each day, in any language, with its own streak.
Controls
- Pick a cell
- Click or tap; arrow keys
- Enter a number
- On-screen number pad, or 1–9 on the keyboard (numpad too)
- Pencil in candidates
- Notes button or N; Shift + number notes it without switching mode
- Erase
- Erase button, Backspace, Delete or 0
- Undo
- Undo button or Ctrl+Z
- Hint
- Hint button or H: fills the selected cell (or the first empty or wrong one)
Modes and options
- Easy
- Solved with obvious cells only: the one number a cell can hold, or the one place a number can go in a row, column or box. Comes with 36 to 42 givens.
- Normal
- Fewer givens (27 to 35) and more searching, but single candidates are still enough.
- Hard
- Needs intermediate techniques: locked candidates in a box and naked or hidden pairs. This is where notes become essential.
- Expert
- Asks for triples, X-Wing or, in the toughest ones, reasoning by cases. Can come with very few givens.
- Daily
- One puzzle a day, the same for everyone. Its difficulty follows the week: Easy on Mondays, Hard on Thursdays and Fridays, Expert on Saturdays. You can share your result (time, mistakes, hints) without revealing the grid.
Rules
- The grid has 81 cells in 9 rows, 9 columns and 9 boxes of 3×3. Some cells start with a fixed number.
- Every row, column and box must end up with the numbers 1 to 9, each exactly once.
- Given numbers can’t be changed. You fill in the rest, in any order you like.
- Notes are helper marks: they record which numbers could go in a cell, but don’t count as an answer.
- The game ends when all 81 cells hold the right number. Your time, mistakes and hints used go into your stats.
Strategy
The golden rule is: don’t guess. If you feel you have to try a number “to see what happens”, there’s almost always a deduction you haven’t spotted yet: look at the notes in the fullest box, or hunt for a pair.
When you place a correct number, the game removes it from the notes around it. Use that: after each new number, check its row, column and box, because that’s where the next solved cells appear.
Go deeper
Tips
- Start with the number that appears most on the grid: with eight of nine already placed, the missing one usually has a single spot.
- Go box by box asking “where can the 1 go?”, then the 2, and so on. It finds more cells than looking cell by cell.
- Tap a number on the grid to highlight all the matching ones: seeing where the 7s are makes it obvious where they can’t go.
- On Hard and Expert, pencil in every candidate in an area before deciding. Advanced techniques show up in the notes, not on the empty grid.
- If “Mark mistakes instantly” is off, double-check before moving on: one wrong number spreads to its whole row, column and box.
Common mistakes
- Guessing a number “to see what happens”. Every puzzle has one solution you can reach by reasoning; if you’re about to guess, look for a pair or a hidden single.
- Looking cell by cell only. Going through each box asking where each number can go finds far more answers.
- Filling the whole grid with notes from the start: scan first, and only take notes once obvious cells stop appearing.
- Carrying on after a wrong number without checking: the error spreads to its row, column and box, and everything you deduce from it is wrong too.
Mechanics
The tags that describe Sudoku. Those with a page lead to similar games.
Glossary
- Candidate (note)
- A number that could still go in an empty Sudoku cell. Candidates are pencilled in small inside the cell and crossed off as numbers are placed in its row, column and box.
- Hidden single
- A number that, within a row, column or box, can only go in one cell, even if that cell could still take other numbers. It’s the technique that solves easy and normal Sudokus.
- Naked pair
- Two cells in the same row, column or box with exactly the same two candidates. Those two numbers are shared between them and can be removed from the rest of the line.
- X-Wing
- An advanced Sudoku technique: if in two rows a number can only go in the same two columns, it takes two opposite corners of that rectangle and can be removed from the other cells of both columns.
- Seed
- A number that decides everything random in a game. With the same seed the dungeon (or the deal) is identical: that’s how the Daily Dungeon and challenge codes work.
FAQ
- Does every puzzle have exactly one solution?
- Yes. Each puzzle is checked by a solver before you see it: if it had two solutions, it’s thrown away.
- How is the difficulty decided?
- The puzzle is solved with human techniques in order (obvious cells, hidden singles, locked candidates, pairs, triples, X-Wing) and graded by the hardest one it needed. The number of givens is also kept within a range for each level.
- Is the daily Sudoku the same in every language?
- Yes: it depends only on the date. Two people playing on the same day get the same puzzle even if they use different languages.
- What counts as a mistake?
- Entering a number that doesn’t match the solution. With mistake marking on, the cell is struck through at once; with it off, only numbers repeated in their row, column or box are marked. Either way the mistake is counted.
- Where is my progress stored?
- In your browser: the game in progress, the day’s puzzle, your times per level, the daily streak and achievements. Nothing is sent to any server.