The Synthego CRISPR Design Tool sorts the guides by using several heuristics, such as cut site on the gene, common exon, and high activity. The CRISPR Design Tool preferentially chooses sequences that occur in earlier exons as an indel in these regions will improve the chances of knocking out the gene’s function. It then preferentially selects guide sequences in exons that are common to various splice variants. Finally, the CRISPR Design Tool uses on-target score (Doench et. al, 2016) and off-targets as a pass/fail criteria to select guide RNA sequences that we recommend for use to knockout a gene.