Black Box Puzzle Online

Black Box is one of the classic one-player logic games in Simon Tatham's Portable Puzzle Collection. Find the hidden balls in the box by bouncing laser beams off them.

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Preparing the game board and controls.

Game Objective

Find every hidden ball inside the box. You cannot see the balls directly; you click edge squares to fire rays into the box, then use the returned edge markers to deduce where the balls must be.

Find the hidden balls in the box by bouncing laser beams off them.

How to Play

Click an edge square to fire a ray from that side.
H means the ray hit a ball head-on and stopped.
R means the ray came back out of the same edge square, either because it was reflected inside the box or because a ball beside the entry point reflected it immediately.
Matching numbers mark a ray's entry and exit: the same number on two edge squares means the ray entered one of them and emerged from the other.
Click inside the box to mark a suspected ball; click again to remove it.
When you have marked the required number of balls, use the green check button to submit.
These puzzles reward careful deduction more than speed. Start with the most constrained clues, eliminate impossible choices step by step, and avoid guessing unless the puzzle specifically calls for it.

Beginner Tips

Ball directly ahead: H, and the ray stops.
Ball on one diagonal-ahead side: the ray turns away to the other side.
Balls on both diagonal-ahead sides: the ray turns back, producing R.
Ball beside the entry point: the ray can reflect immediately and produce R.
If a ray returns to its original entry after several turns, that is also R.
Use H results first: they tell you that some square on that straight line contains a ball. Fire crossing rays from another side to narrow down which square it is.
Use numbered pairs next: trace a possible path from one number to the matching number, bending the path away from any candidate balls. If a candidate ball would send the ray to the wrong exit, rule it out.
Do not guess all balls at once. Build a map of impossible squares, place balls only when several ray results agree, then submit after the required number of balls is marked.