Methyltetrazine-PEG3-amine is a short PEG linker featuring a methyltetrazine and a primary amine. The methyltetrazine can be reacted with TCO for a high-yield click reaction while the amine easily reacts with carboxylic acids in the presence of reagents such as HATU or EDC to form amide bonds. Amines are also useful in reductive amination, and heterocyclic chemistry.