Black Box

from Simon Tatham's Portable Puzzle Collection


If you've been reading this message for more than a second or two, then this WebAssembly puzzle doesn't seem to be working in your web browser. Sorry!

More information

Most modern browsers should support WASM. I've had reports of success from:

If this puzzle isn't working in one of those browsers (or a later version), check to see whether you have any local configuration that might have turned off WebAssembly completely, or some kind of blocking software that might have prevented the WASM code from being downloaded in the first place.

(For example, in Firefox, it's possible to turn off WASM completely by setting javascript.options.wasm to false in the about:config interface. If you've done that, or something analogous in another browser, this puzzle won't run.)

In other browsers, the problem might be that WebAssembly isn't supported at all (for example, Internet Explorer 11), or that a browser update is needed.

If you think that your browser should support WebAssembly, but this puzzle still isn't running, then please report the problem, including as much diagnostic information as you can find.

In particular, try opening your browser's Javascript error console and then reloading this page, and tell me if it reports any error messages.

Also, if your browser has a network diagnostic tab, try the same experiment, to make sure it is successfully loading both of the auxiliary files blackbox.js and blackbox.wasm.


Determine where the hidden balls are in the box, by observing the behaviour of light beams fired into the box from the sides.

Click in a square around the edge of the box to send a beam into the box. Possible results are 'H' (the beam hit a ball dead-on and stopped), 'R' (the beam was either reflected back the way it came or there was a ball just to one side of its entry point) or a number appearing in two squares (indicating that the beam entered one of those squares and emerged from the other).

Click in the middle of the box to place your guessed ball positions. When you have placed enough, a green button will appear in the top left; click that to indicate that you think you have the answer. You can also right-click to mark squares as definitely known.

Full instructions | Back to main puzzles page


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(thanks to chiark for hosting this page)
(last modified on Wed Apr 28 01:47:05 2021)