The precision of Twist Bioscience’s technology allows for the sampling of large variant space with predefined base by base composition and ratio control. Other library fabrication methods, such as NNN and NNK, result in redundant codons that lead to poor control over diversity and uneven distribution of amino acids. Advancements in Twist’s silicon-based DNA synthesis platform enables precise synthesis of high diversity domain libraries at uniform ratios. Every Twist library is validated by next-generation sequencing to determine variants that are present, which can confirm both positive and negative hits from screens.