Why every Glowstring level is built backwards

Glowstring is a puzzle about lanterns tied together with strings. Tap one and it flips, along with every lantern tied to it. Light the whole street to finish the level.

None of the levels are designed by hand. A generator builds all of them, which raises a problem: how do you know each one can be solved?

Start from the solution

Each level is built in reverse. The generator draws lanterns and strings with no crossings, picks the taps that will solve it, and undoes those taps starting from the fully lit street. Every level has a solution because it began as one.

Finding par

A solver then works out the exact minimum number of taps, which becomes the level's par. Match par for 3 stars, or stay within 2 taps of it for 2 stars. On scissor levels it also tries every possible cut and only keeps levels where the scissors are actually needed.

New rules every 20 levels

• First Night: tap to flip
• Loose Strings: swipe across a string to cut it
• Embers: lanterns go from off to ember to lit
• Currents: some strings carry the spark one way only
• The Fair: every rule on the same street

After that come Nights that mix rules at random and grow up to 18 lanterns. The first 300 levels ship with the game, and the rest are generated on your phone while you play.

The demo on this page has 5 levels from the first chapter. The full game is on Google Play.