Exterminator is a game in which you are chased by robots. The robots are relentless but stupid. Your job is to escape the robots by destroying them.

The game is played on a grid. Each turn, you may move one square in any direction (including diagonally) or stay put. After you make your move, the robots will all move. The robots will always move directly toward you. If two (or more) robots to crash into each other, they will be destroyed and leave a heap of toxic wreckage behind. If a robot runs into a toxic heap, it will be destroyed also. If you run into a robot or a toxic heap, or if a robot catches you, you're dead.

Since the robots always move directly toward you and are oblivious to any other part of their surroundings, you can try to lure the robots into each other or into the toxic wreckage, thereby destroying them. You earn a point for each robot you destroy; when all the robots on a level are destroyed, you advance to the next level where there will be more robots.

There are two additional moves you can make besides moving from one square to another. Once per level, you can "zap" any and all robots in any of the eight squares adjacent to you, destroying them. You may also choose to "teleport" to a random new location on the playfield. (Note, however, that there is a very small chance that the new location you teleport to will be the same place you teleport from.) The availability of the "teleport" option depends upon the mode of play.

When playing in "Limited Safe" mode, you may only use the "teleport" move twice per level (and only once starting with level 25). However, these teleports are guaranteed to be "safe" teleports -- that is, you will never be teleported into a robot, on a toxic heap, or to a place next to a robot where it will catch you when it moves. After your safe teleports are used up, you can't make a teleport move again until the next level.

When playing in "Limited Safe; Unlimited Unsafe" mode, the first two times you teleport will be "safe" teleports, as described above. (Starting with level 25, only the first is guaranteed to be safe.) Thereafter, you may continue to teleport for as many times as you like, but the teleports are not guaranteed to be safe. You still won't be teleported on top of robots or toxic heaps, but you might be teleported next to a robot, in which case it will catch you when it moves.

When playing in "Unlimited Unsafe Teleports" mode, there is no limit to the number of teleport moves you can make per level, but none of them are guaranteed to be safe teleports.

You can save your game by bookmarking the page in the game you want to come back to later. This isn't always safe; if you bookmark a game immediately after a new level appears, the level will be generated again, differently, when you return to the bookmark. Also, if you bookmark immediately after a teleport move, the move will be redone when you return, and you probably won't end up in the same place. Bookmarking the game at any other time is guaranteed to preserve the state of the game accurately.

Cheating at this game is possible but discouraged as a general rule. However, on occasion it can be fun to play around with the game engine. The simplest way to cheat is to hit the "back" button on your browser when something happens that you don't like. You can also cheat by modifying the URL at a particular point in the game. Notice that the URL is comprised of name=value pairs, separated by ampersands. The letter(s) or number(s) before the equals sign is the name, and what comes after it is the value. If you modify some of the values you can change the state of the game. You can experiment if you like. Below are some specific things you can do.

Immediately after the generation of a new level, change the value of l to jump to a different level. (The value of l should be one less than the level number you'd like to go to; also, if this value is changed in the middle of a level, the change won't take effect until the current level is finished.) Change the value of t to some high number to receive that many safe teleports for that level, regardless of the game mode you're in. Change the value of p to set the number of points you have. After you have made a "zap" move, change the value of z to 0 to be able to "zap" again on that level.