Quick Walkthrough
1 — Goal
Fill every row, column and 2×2 box with numbers 1–4 without repeats.
2 — Notes
Use pencil marks (if available) or trial-and-error for candidates.
3 — Strategy
Scan for forced numbers, then look for single-candidate cells.
4 — Hints
Use the "Hint" or "Check" buttons on the Play screen when stuck.
Interactive Example
Open the Play screen and try filling a 4×4 grid; use Undo or Reset as needed.