Enzymatic degradation of cellulosic biomass to the composite monosaccharides requires the combined and synergistic action of an array of enzymes, including enzymes that target the glycosidic linkages of cellulose and arabinoxylan. Complete hydrolysis of cellulose requires exoglucanases, endoglucanases, and glucosidases, while complete hydrolysis of arabinoxylans requires endo-xylanases which hydrolyze the xylan backbone main chain to release xylooligomers, and β-xylosidases which catalyze hydrolysis of xylooligomers to D-xylose residues. In addition, there are also numerous enzyme activities that release less common or biomass-specific side chains, as well as debranching activities, both of which also play a crucial role in complete cellulosic biomass depolymerization. Often, the native enzymes are deficient in one or more process-specific parameters, and efforts are currently underway in our group and others to engineer these enzymes using various techniques including random mutagenesis. Concerning the latter, while a high degree of mutagenesis may uncover beneficial mutations, these libraries usually require a primary active/inactive purification screen. We present here the validation of such a screen using suitable methylumbelliferyl artificial substrates and a β-xylosidase random mutagenesis library expressed in E. coli, and the extension of the same general technique to several other glycosylhydrolase activities.