The most precise measurand available to science is the frequency of ultra-stable lasers. With a relative deviation of 4 × 10−17 over a wide range of measuring times between one second and 100 seconds, the smallest effects in nature can thus be made measurable. To enable cutting-edge precision, the laser frequency is stabilized to an external optical cavity. This complex optical device must be manufactured to the highest standards and shielded from environmental influences. Given this assumption, the smallest internal sources of perturbation become dominant, namely the internal noise of the optical components. In this work, we present the optimization of all relevant noise sources from all components of the frequency-stabilized laser. We discuss the correlation between each individual noise source and the different parameters of the system and discover the significance of the mirrors. The optimized laser offers a design stability of 8 × 10−18 for an operation at room temperature for measuring times between one second and 100 seconds.