How to play Black Box: trace the laser and find the hidden balls
Black Box is a deduction puzzle from Simon Tatham’s Portable Puzzle Collection. Fire beams from the edge of a box, read where each beam stops, reflects or emerges, and use those clues to place the hidden balls.
Read the beam results
Choose a square along the outside edge to fire a beam through the grid. H means it hit a ball directly. R means it returned to its entry point after a reflection, including a deflection caused by a ball beside the entry square. A number at the entry and matching number at the exit describe one beam passing through the box.
The board shows the observed path, not the ball itself. Compare results from different edges and trace which placements could explain every beam.
Mark and check your guesses
Tap or click inside the box to place a guessed ball. Tap or click the same square again to remove it. On touch screens, switch on Mark mode above the board to mark a square you know; switch Mark mode off before firing or changing guesses.
When you have placed the required number of guesses, use the green check button in the game. Some different arrangements can have the same complete set of beam results, so the rules allow any arrangement that matches the clues.
Controls and saving
Touch uses tap; a mouse uses left-click to fire or guess and right-click to mark known cells. The upstream menu and status messages remain in English. The localized Mark mode is a Denny Games touch adaptation.
The game runs locally in an isolated frame. Puzzle progress is not saved. Restarting or reloading opens a fresh puzzle; there is no account or online score.