Standard Sudoku rules#
A completed 9×9 grid contains the digits 1–9 exactly once in every row, column, and 3×3 box. Starting digits are called givens and cannot be changed during normal play.
Validity and solutions#
Lab Sudoku rejects starting grids that already duplicate a digit in a row, column, or box, and grids with no valid solution. A manually entered puzzle with multiple solutions can be accepted as a beta case, but solution-dependent mistake checking and Guided Hints are limited.
Difficulty#
Lab Sudoku groups built-in puzzles into Simple, Easy, Intermediate, Expert, and Diabolical levels. Difficulty is a guide to the expected solving challenge, not a guaranteed completion time. Your familiarity with candidates and techniques can make two puzzles at the same level feel different.
Supported entry methods#
You can start a built-in puzzle, enter givens manually, or use camera import to scan a printed or on-screen grid. Lab Sudoku does not currently advertise a public link or text-file import format; use manual entry when moving a puzzle from plain text.
Text notation for support#
When reporting a puzzle, an 81-character row-by-row string is compact and unambiguous. Use digits 1–9 for givens and . for empty cells. For example:
..6.1........4.2....8.....61....34..5......693...2.8.1..1..4..3.2...81.....3..52.This notation is useful in a support request; it is not a promise that the app can paste or import the string directly.
Sharing a puzzle#
If the current app version does not show a Share action, send the 81-character notation or a clear, tightly cropped screenshot. Never include unrelated personal information around a photographed puzzle.