RNA-binding and decapping enzyme that catalyzes the cleavage of the cap structure of snoRNAs in a metal-dependent manner. Has diphosphatase activity and removes m7G caps from U8 snoRNA (PubMed:18820299). May catalyze the cleavage of the cap structure on mRNAs. May also act as a phosphatase; hydrolyzes the non-canonical purine nucleotides inosine diphosphate (IDP) and deoxyinosine diphosphate (dITP) (By similarity). May bind to the U8 snoRNA. a 5'-end (N(7)-methyl 5'-triphosphoguanosine)-ribonucleoside in mRNA + H2O = a 5'-end phospho-ribonucleoside in mRNA + 2 H(+) + N(7)-methyl-GDP H2O + IDP = H(+) + IMP + phosphate dIDP + H2O = dIMP + H(+) + phosphate Decapping activity is higher in the presence of manganese than in Magnesium or cobalt. Homodimer. Belongs to the Nudix hydrolase family. NUDT16 subfamily.