Rules & objective
Mines are placed on the first real open, protecting that cell and all its neighbors. Connected empty areas and their numbered borders open automatically. Flags are guesses, not known mines; right-click or flag tap-mode toggles them and protects marked cells from direct opening. A revealed number can open its remaining unflagged neighbors when adjacent flag count matches; wrong flags may still explode a mine. Open every non-mine to win without flagging all mines; final flags are automatic. A mine hit ends the field and shows mines/wrong flags; Undo permits practice. Hints use only revealed equations and total mine count, ignore guessed flags and never inspect hidden layout; no certainty is reported honestly. Random fields may require guesses, with no no-guess promise. Reset retains the same field and opening; New uses a fresh seed. Assists/mine hits do not decrease on Undo. Timer runs only while visible with rules closed. Zoom, drag or row/column selection reaches large fields; a drag never opens a cell.
Square clues count all eight surrounding cells; edges do not wrap.
Controls
←↑↓→ Cell · Enter Open/Hint · Space Flag · C Chord · H Hint · U Undo · F Fullscreen
Worked example
If a clue of one has one genuinely established neighboring mine, its other neighbors are safe. A flag alone is not proof of a mine.