Genetically-encoded peptide screening platforms, such as phage display, mRNA display and the related random non-standard peptides integrated discovery (RaPID) system, provide powerful approaches to identify peptide hits from enormous libraries of cyclic peptides (up to 10 13 sequences). These platforms have been used successfully to identify potent reversible chemical tools and drug candidates to a wide range of targets. Recently these screening approaches have been modified to promote bias towards the discovery of irreversible covalent inhibitors; reactive moieties have been introduced into the peptide libraries alongside denaturing guanidine washes during the peptide selection step. For example, a modified phage display protocol has been used to identify de novo covalent peptide inhibitors through post-translational modification of peptide libraries with warheads into a fixed position -either within the cyclisation linker or at reduced disulphide bonds. Other methods to introduce unnatural chemistry into peptides have also been developed, including through use of modified aminoacyl tRNA synthetases, chemical aminoacylation of tRNA or use of aminoacylating ribozymes, known as flexizymes. The RaPID system offers a route to identify chemically diverse peptide binders through encoding non-canonical amino acids in displayed peptides using the flexizyme-mediated flexible in vitro translation (FIT) system. This enables both facile peptide cyclisation and the potential for direct warhead incorporation. Unlike in the phage display approaches this allows incorporation of the covalent warhead at variable positions in the peptide macrocycle. Recently, this strategy has been used to incorporate phenylselenocysteine into RaPID libraries, which was then post-translationally modified to yield a dehydroalanine warhead. Photoreactive covalent peptides have also been identified through incorporation of a benzophenone moiety. However, the ability to directly encode an unmasked electrophilic warhead within displayed libraries, rather than relying on post-translational modification, has not yet been exploited.