How to use the no-guess board builder

Choose any grid dimensions up to 100 rows by 100 columns and set the total mine count. Then click a square to cycle it through covered, blank, mine, and clues 1 through 8. Shift-click cycles backward. The translucent result on every covered square shows what could legally be underneath it.

A question mark means the current clues leave many possibilities. When only a few outcomes remain, the square shows all of them. A square displaying both a mine and a 2 could legally be either one in different boards that satisfy the same clues.

What makes a board no-guess

A no-guess position has at least one covered square that every valid completion agrees is safe or every completion agrees is a mine. Revealing or flagging that forced square may create the next deduction.

If the board is valid but every covered square still has several possible contents, the position currently requires a guess. Add a known clue or continue from another part of the board.

How the checker reads numbers

Each numbered square is safe and must touch exactly that many mines in its eight surrounding squares. A blank is a zero clue, so every adjacent square must be safe. A marked mine counts toward every clue it touches.

The total mine field setting is a global clue. It can prove distant squares safe or dangerous even when no numbered square touches them.

Why impossible clues turn orange

The editor deliberately allows contradictions so it can explain them. A clue turns orange when it already touches too many marked mines or cannot possibly reach its number with the covered neighbors left.

For example, an 8 with five surrounding blanks is impossible. The 8 and its neighbors are highlighted, but your entries remain unchanged so you can inspect and repair the position.

Use possible contents, not probabilities

The overlays answer whether an outcome is logically possible, not how likely it is. If a square shows a mine and a 2, both outcomes occur in at least one complete board, but they need not occur equally often.

No-guess play depends on certainty. Act when every valid board agrees; treat all other overlays as reminders of what the clues have not resolved.

A reliable deduction routine

  • Enter every revealed blank and number exactly as it appears.
  • Add only mines you have proved, not tentative flags.
  • Set the total number of mines for the whole board.
  • Repair any orange contradictions before using deductions.
  • Look for a covered square showing only a mine or only one safe value.
  • Update the board after every reveal and repeat.