Azido-modified analogue of UDP-GlcNAc; serves as a substrate for O-GlcNAc transferase (OGT) and N-acetylglucosaminyltransferases enabling metabolic and chemoenzymatic glycan labeling; the azidoacetyl handle permits bioorthogonal conjugation via copper-catalyzed azide–alkyne cycloaddition (CuAAC) and strain-promoted azide–alkyne cycloaddition (SPAAC); can be epimerized to UDP-GalNAz by UDP-galactose-4-epimerase (GALE); widely used in O-GlcNAc proteomics, glycan imaging, and selective probing of intracellular O-GlcNAcylation