The precise interplay between the mRNA codon and the tRNA anticodon is crucial for ensuring efficient and accurate translation by the ribosome. The insertion of RNA nucleobase derivatives in the mRNA allowed us to modulate the stability of the codon-anticodon interaction in the decoding site of bacterial and eukaryotic ribosomes, allowing an in-depth analysis of codon recognition. In addition to a quantitative analysis of the protein products that are formed in dependence of the modified codons, the interpretation of these RNA nucleobase derivatives by the ribosomal decoding site was also determined. For each modification, the translated peptides from the bacterial and eukaryotic systems were purified and analyzed by mass spectrometry.