We present a polymerization-based assay for determining the potency of cellulolytic enzyme formulations on pretreated biomass substrates. Our system relies on monitoring the autofluorescence of cellulose and measuring the attenuation of this fluorescent signal as a hydrogel consisting of poly(ethylene glycol) (PEG) polymerizes on top of the cellulose in response to glucose produced during saccharification. The one-pot method we present is label-free, rapid, highly sensitive, and requires only a single pipetting step. Using model enzyme formulations derived from Trichoderma reesei, Trichoderma longibrachiatum, Talaromyces emersonii and recombinant bacterial minicellulosomes from Clostridium thermocellum, we demonstrate the ability to differentiate enzyme performance based on differences in thermostability, cellulose-binding domain targeting, and endo/exoglucanase synergy. On the basis of its ease of use, we expect this cellulase assay platform to be applicable to enzyme screening for improved bioconversion of lignocellulosic biomass.