A system, a machine-readable storage medium storing instructions, and a computer-implemented method are described herein for a System Tuner for customizing a player's experience. A System Tuner selects a hardness quotient, based on a player skill level, from a hardness quotient range, the player skill level for a player is calculated by a client computing device based at least on a plurality of game moves in a first game level completed by the player. The System Tuner provides the hardness quotient to a level definition file for a second game level. The level definition file modifies at least one feature of the second game level according to the hardness quotient. The System Tuner modifies the hardness quotient range based at least on a performance of the plurality of player's in the second game level and the respective hardness quotients assigned to each of those players for their game play in the second game level.