Sudoku

Fill a 9×9 grid so every row, column, and 3×3 box holds the digits 1–9 once. Easy, Medium, and Hard puzzles from a fixed library — notes, check, and undo included.

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Rules and help

Sudoku is a placement puzzle. You never need arithmetic — only logic. Each puzzle on Play Solo comes from a preset library at Easy, Medium, or Hard.

How to play

  • Goal. Complete the grid so each row, each column, and each of the nine 3×3 boxes contains the digits 1 through 9 with no repeats.
  • Given digits. Clues start filled and locked. You enter the rest in empty cells.
  • Notes (candidates). Use notes mode to pencil possible digits in a cell. Clear or replace them as you narrow options.
  • Check. Duplicates in a row, column, or box highlight as you type. Check compares filled cells to the solution and marks any that do not belong; it does not reveal the correct digit.
  • Undo. Step back mistaken entries without restarting the puzzle.
  • Win. The puzzle is complete when every cell is filled correctly with no conflicts.
  • Timer & notes. A timer starts on your first entry; Pause covers the grid. Notes mode pencils candidates; placing a digit clears that candidate from the row, column, and box. Previous / Next step through the library at the same difficulty; progress stays on this device.

Tips

  • Scan for singles: a digit that can go in only one cell of a row, column, or box — place it before deep candidate work.
  • Keep notes tidy. When you place a digit, erase that candidate from the rest of its row, column, and box.
  • On Hard, look for naked pairs and locked candidates before guessing; this build is meant to be solved by logic.
  • Use Check sparingly as a safety net, not as a substitute for scanning — you learn more by finding the conflict yourself.
  • If two candidates look symmetric, pick a fresh empty region with more givens nearby; progress there often unlocks the stalemate.
  • When a digit is placed nine times, its button quietens so you can see what is left.

Playing on a phone or tablet

Tap a digit, then tap each cell that should hold it. Turn on Notes and do the same to pencil candidates. Pause covers the grid and stops the timer if you need to step away.

Frequently asked questions

Are puzzles randomly generated?
No. Easy, Medium, and Hard each draw from a prepared library so difficulty stays consistent.
Do I need to guess?
These puzzles are designed to be finished with logic. If you feel stuck, add notes and re-scan for singles and pairs.
Does every puzzle have a solution?
Yes. Each library puzzle has one solution. Digits that conflict in a row, column, or box highlight as you enter them.
Are my notes removed automatically?
When you place a digit, that candidate is cleared from the same row, column, and box. Other notes stay until you change them.
Can I pause the timer?
Yes. Pause covers the grid so you can step away without seeing the board. The timer stops until you resume.

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