Peptide and protein bioconjugation sees ever-growing applications in the pharmaceutical sector. Novel strategies and reagents that can address the chemo- and regioselectivity issues inherent to these biomolecules, while delivering stable and functionalizable conjugates, are therefore needed. Herein, we introduce the crosslinking ethynylbenziodazolone (EBZ) reagent JW-AM-005 for the conjugation of peptides and proteins through the selective linkage of cysteine residues. This easily accessed compound gives access to peptide dimers or stapled peptides under mild and tuneable conditions. Applied to the antibody fragment of antigen binding (Fab) species, JW-AM-005 delivered rebridged proteins in a one-pot three-reaction process with high regioselectivity, outperforming the standard reagents commonly used for this transformation.|Easily accessible crosslinking ethynylbenziodazolone (EBZ) JW-AM-005 enables the conjugation of peptides and proteins through the selective linkage of cysteine residues. Peptide dimers or stapled peptides were obtained under mild and tuneable conditions. The rebridging of antibody fragments was also performed in a one-pot three-reaction process with high regioselectivity, outperforming the standard reagents commonly used for this transformation.+image