Fog of War Sudoku: Rules and Solving Strategy

Understand what the fog conceals

Fog of War Sudoku begins with part of the grid hidden. The fog may conceal cells, given digits, region borders, lines, cages, dots, or other variant clues. Entering a correct digit reveals more of the board according to the puzzle's stated reveal rule. A common version clears nearby cells around the placement, but some puzzles reveal information elsewhere or use a custom pattern. Read the instructions before solving and treat unrevealed content as unknown. Standard row, column, and box rules still apply to the visible grid unless the puzzle says otherwise. Good Fog of War puzzles are intended to progress logically without blind guessing. You should never assume that an unseen cell is empty, that a hidden line ends at the fog boundary, or that a partially visible cage contains only the cells you can currently see. Shapedoku does not currently use a fog mode, but its clear Notes, four difficulty levels, and first free Hint are useful for practicing the logical discipline that fog puzzles demand.

Solve from the visible frontier

The frontier is the boundary between revealed and hidden information. Start with ordinary singles and direct consequences in the visible area. Prioritize placements that are fully proven, not placements that merely seem likely to uncover a useful region. When several forced moves are available, a move near the frontier often reveals more clues and may be strategically helpful, but logical certainty comes first. Keep Notes only for candidates supported by visible information. If a hidden clue might later remove a candidate, that does not make the current note wrong; it simply means the note is provisional. After each correct entry, stop and inspect everything newly revealed before making another move. A new given digit may alter several candidate lists, while a newly exposed line or cage may change the interpretation of cells you had already considered. Fog puzzles punish momentum when momentum becomes an excuse not to reread the board.

Avoid assumptions about partial clues

Partial geometry is the main source of errors. A colored line disappearing into fog may continue, turn, branch, or end, depending on the puzzle. A visible cage border may hide additional cells. An outside clue may point along a diagonal whose later cells are still concealed. Apply only the portion of a rule that is completely visible and defined. If two revealed cells are clearly adjacent on one continuous line, their relationship can be used. If the line's endpoint is hidden, do not apply endpoint-specific logic yet. The same restraint applies to negative constraints. You cannot conclude that an unseen border lacks a dot or marker. Keep a small mental distinction between confirmed facts and pending structure. When stuck, rescan revealed rows, columns, boxes, and clue fragments rather than testing digits. A logically forced placement somewhere in the visible area is usually the key that lifts the next section of fog. Once the full board is revealed, the puzzle becomes an ordinary variant Sudoku, so return to its standard techniques and clean any provisional Notes.

1. Read the exact reveal rule before entering the first digit.
2. Use only visible clues and standard Sudoku restrictions to prove placements.
3. Prefer a frontier placement only when it is already logically forced.
4. Pause after every reveal and inspect all new digits, borders, and line segments.
5. Do not assume that a partial cage, line, or outside clue ends at the fog.
6. Separate provisional candidates from confirmed structural facts and never guess to reveal more.