Sudoku

1 click (default): pick a digit on the panel, then tap cells to fill or pencil-mark.
Normal mode: tap 1 click to switch off. Select a cell, then use the digit panel or keyboard. Tap the same cell again to deselect.
Pencil: enter small candidate notes. Fill: enter solved digits. Color: pick a digit and color, then tap pencil notes to frame them in green, red, or purple.
Helper, Hints, and Manual tabs switch between overlays, technique hints, and puzzle loading tools.
Auto Pencil toggles all legal candidates on or off; each click is undoable. Undo reverses your last change; Redo restores it.

Tap an empty cell to select it (green highlight). Its pencil notes appear active on the digit panel.
Tap a filled cell to highlight every cell with that digit. Tap any of those cells again to clear the highlight.
Digit panel taps apply to the selected cell; they do not highlight the whole board.

Expand the Hints tab for Basic and Advanced techniques.
Availability: Disable, Selected number (needs a digit), or All number. Check/X show when enabled.
Helper can overlay bi-value cells or strong links (Row / Col / Box / All number filters).

New starts a random puzzle by difficulty. Reset restores the original givens.
Use the Manual tab to paste a puzzle, load from text, or copy board state (with or without pencil notes).
Paste 81 characters (0 or . for empty) or notation like 12[34][]….

Quick Spotting Tips