InvisiClues were hint booklets sold by Infocom to help players solve puzzles in their interactive fiction computer games. Before Infocom's games exploded in popularity, players could request hints by mail and receive a type-written sheet in response. When the number of requests proved unmanageable, Infocom began the Zork Users Group pay-per-hint telephone system. The invention of InvisiClues replaced this system and was revolutionary: a player could often buy a hint book at the same time and at the same location as the game itself.

Questions relating to the game were printed in the book, for example, the InvisiClues for Zork I contained the question "How can I kill the songbird?" An "empty" box was located below or following the text. The answer to each question was revealed by using a special highlighter-like marker that came with the book; this marker contained a special solution that made the previously hidden answers visible. Over time, the ink degraded and the text reverted to invisibility.

To discourage players from accidentally learning what awaited by reading all the questions, each booklet contained a number of plausible-sounding "fake" questions. Revealing these answers usually resulted in a mild scolding. Several "non-puzzles" also had questions, such as the songbird example used above. The answer to these was usually a tersely-worded statement saying "You can't do that", often followed by one or more items reading "This space intentionally left blank."

Some books also contained maps and other supplements that aided in solving the games.

Though InvisiClues, like the games themselves, are no longer available, a few Internet sites have recreated the booklets. Typically, either all the answers are printed normally on the site or the user must "highlight" a section by clicking and dragging the mouse to reveal the hints.

External link

• Site with InvisiClues to some Infocom games