Tools are resources that extend the player’s ability take action in a game. They often use meters or currency, like ammunition for a rifle, supplies for a restaurant or possession of the ball for an NFL offense. Some are mobile, such as an object that you can pick up, whereas others are fixed in the game, such as a switch to open a door.
Games with many tool classes tend to suffer robustness issues. As the player experiments with different kinds of tool, he will probably find an exploit (a combination that makes the game easy to win, and thus boring) because the game designer simply can’t balance them all.
Though it may appear that a successful game has lots of tool choices, there are only a few classes. Each has a basic loop that repeats consistently throughout the game, and each has many individual tools that have slightly different meter and currency requirements.