Prodrugs have the potential for improving therapeutic index and expanding drug targets, but current prodrug activation strategies that are responsive to endogenous stimuli can result in unintended drug release and systemic toxicity. Here, the authors report 3-vinyl−6-oxymethyltetrazine (voTz) as an all-in-one reagent for modular preparation of tetrazine-caged prodrugs and chemoselective labeling of peptides to produce bioorthogonal activable peptide-prodrug conjugates.