The Gamemaster rule checker is a special "configuration" of the Sierra Interactive Development Environment. It allows users to edit and apply game rules written in GDL2. Using the rule checker to check new game rules is highly recommended before using those rules in playing games.

The rule checker can be found here .

The Sierra splash page is at the top in the middle and contains controls for customizing the system. The command bar across the top provides access to menus concerning files, tools, and worksheets. For checking game descriptions, there is no need to use these capabilities. If you want to learn more about Sierra, click here.

The game rules appear in the window immediately below the splash page. The current state of the game is shown in the window on the upper left (labeled Lambda). The initial state of the game is shown in the window immediately below Lambda. Below that is an Execute window, which allows you to perform game actions. The window on the upper right shows legal moves in the current state. The window below that shows rewards for the various players. The window on the lower right indicates whether or not the game is terminal.

When you open the rule checker, you will see a collection of interlinked windows. To help newcomers, the rule checker is pre-populated with the rules of Tic Tac Toe. To use the rule checker, simply replace these rules with your own and press Update. The other windows (except for Lambda) will update automatically. Copy the initial state and paste into Lambda and press Update in that window. Once again, the windows will update automatically. To make a move in the game, select a legal move from the window in the upper right, paste into the Action field of the Execute window and press Execute. Once again, the windows will update automatically. To restart a game, simply copy the initial state into the Lambda window and press Update. If you do not like the behavior you see, edit your rules, press Update, and repeat.