Endosulfatase involved in the degradation of the glycosaminoglycans (GAGs) chondroitin sulfate (CS) and dermatan sulfate (DS). Efficiently hydrolyzes sulfate groups from a broad range of substrate size, including disaccharide to high molecular weight CS and DS polymers. Has a strict specificity for the 4-O-sulfate groups of galactosamine (PubMed:25002587). GAG-specific sulfatases play a key role in the persistence of the major human gut symbiont B.thetaiotaomicron in the host gastrointestinal tract (PubMed:25002587). The conversion to 3-oxoalanine (also known as C-formylglycine, FGly), of a serine or cysteine residue in prokaryotes and of a cysteine residue in eukaryotes, is critical for catalytic activity. Belongs to the sulfatase family.