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Puzzle / 5–15 min

Black Box

Hidden balls bend or stop light inside a grid. Fire beams from the edges, compare hits, reflections and paired exits, then work out which squares can hold a ball. This calm deduction puzzle has no clock. Denny Games adds a touch mark mode; the original in-game menu remains in English.

Play now ↗
TouchMouse
Black Box — Original Denny Games illustration of a laser beam tracing a path past hidden spheres inside a dark grid
Black Box — actual game board
Actual game board · Chromium

How to play

  1. Tap or click a square around the edge to fire a laser beam into the box.
  2. H means the beam hit a ball. R means it reflected or passed a ball beside its entry square. Matching numbers show where a beam entered and exited.
  3. Tap or click a square inside the box to add or remove a guessed ball. Turn on Mark mode to mark a square as known on touch screens.
  4. When your guesses are ready, use the green check button. Some different ball layouts can produce exactly the same beam results.

Learn the rules

How to play Black Box ↗

Make your move

  • Touch: tap an edge square to fire and a board square to guess. Turn Mark mode on to mark known squares, then turn it off before firing or guessing.
  • Mouse: left-click to fire or guess; right-click a square to mark it as known.
  • The original game menu and status text are in English. Puzzle progress starts fresh after restart or reload.

A small head start

  • A direct hit stops a beam at the first ball in its path.
  • A reflection can come from a ball beside the entry square, so compare beams from nearby edges.
  • An exit number pairs with the matching entry number; reason about the path between both ends.

Compatibility notes

Touch and keyboard controls are implemented. Physical phones, controllers and Tesla browsers await device testing.

Play style: Point and move. This game keeps its own score table only while this play page stays open. Leaving or reloading starts fresh.

Check this game on your device ↗

Compatibility · Input check

Credits & source

Simon Tatham’s Portable Puzzle Collection · Black Box is part of Simon Tatham’s Portable Puzzle Collection. This release pins source commit 616da16f25da428ccda805536209095bd062676e and the official JavaScript/WebAssembly artifacts; hashes and the local lifecycle/touch adaptations are published in the local notices. The upstream menu and status text remain in English. Denny Games translates the host guide and adds touch marking. Puzzle progress is not saved.. MIT notices and source · · Official collection and MIT source · Pinned upstream source and official browser build

Updated: 2026-10-25. Free to play. Pages may contain disclosed affiliate links; Google ads are inactive.

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