Abstract: Embodiments disclosed herein provide methods, including computer-implemented methods, for designing guide sequence which may be incorporated into custom, large scale guide sequence libraries. The methods require only a list of target genes as input and utilize on target and off target scores to generate an optimal set of guide sequences for a set of target genes. In certain embodiments, the methods may also utilize multi-tissue RNA-sequencing data and/or protein annotation to design targets to genes that are highly expressed and/or contain a functional protein domain. The invention further comprises guide libraries, cells comprising said guide libraries. Computer-implemented embodiments further improve computer system function by reducing excessive user wait time through the use of data structures that reduce search from linear to logarithmic time.