Klax, ™ Atari Games & © Tengen Inc, features a conveyor belt at the top of the screen. It constantly rolls toward the playing area, delivering a steady supply of blocks. The player controls a small device which sits at the interface between the conveyor belt and the playing area, and can be moved left and right to catch the blocks and either deposit them in the playing area or throw them back up the conveyor belt in an attempt to strategically align colored blocks. The device can hold up to five blocks. A block which is not caught and placed in the playing area or pushed back up the belt is considered a drop. The blocks are solid colours, but there is also a flashing block which can be used as a wildcard on any colour.
Klax consists of 100 levels grouped into blocks of five. At the beginning of the game and after each fifth level (levels divisible by five, except for Levels 95 and 100), a player can choose to skip five or ten levels. Skipping levels gives bonus points and more drops.
In the playing area, blocks can be eliminated by getting three or more "Klaxes" (groups) of the same color in a line. The line may be horizontal, vertical, or diagonal. A multiple grouping (i.e., one vertical and horizontal) counts as two Klaxes. In a few early levels, the player may be able to warp ahead 45 levels if he builds a large X with five blocks for each diagonal. Doing so awards a 600,000 point bonus (plus any due warp bonus).
There are 100 levels in Klax, and a score of 250,000 is required to complete the last level. The unreleased Atari 7800 version added three "impossible" levels.
Scoring can vary between versions. A player also earns a multiplier for creating multiple Klaxs and combinations. Multipliers can take effect in two variations. Most commonly, a player receives a bonus multiplier for each Klax created, which continues if he/she creates a combination. For example, if the player makes a vertical-3 and a diagonal-3 at the same time, the score is 50 + 5,000 = 5,050 * 2 = 10,100 points. If the player then combos into a diagonal-3, the player receives 5,000 * 3 = 15,000 points. The second variation is that the player receives a bonus multiplier only if the player creates a combination. This multiplier increases only by one in each combo iteration.