Feed-forward networks are a major source of nonlinear transformation in modern language models, yet their internal representation dynamics are often summarized only through loss or activation statistics. NerVE introduces an eigenspectrum-based framework for analyzing how nonlinearities reshape representation geometry across transformer feed-forward layers. By tracking spectral entropy, participation ratio, effective rank, and divergence-based measures before and after nonlinear transformations, the framework reveals how representation capacity is amplified, compressed, or reorganized across layers and scales.