Post-translational modifications (PTMs) are critical to protein function, yet the function of most known modification sites remains uncharacterized. CRISPR-mediated phenotypic screens using base editors offer a powerful approach to dissecting PTM function at scale. However, existing sgRNA design tools for base editing applications are DNA-centric and lack the throughput required to integrate seamlessly with mass-spectrometry-based proteomics experimental outputs. We introduce protein editing in R, PrEditR, an open-source, protein-centric tool for high-throughput sgRNA design for custom base editor screens. PrEditR enables users to designate specific amino acid residues in proteins and design protospacer sequences to target the endogenous gene to install missense mutations via base editors.