Catalyzes the specific dephosphorylation of phosphoarginine residues in proteins. Probably counteracts the protein arginine kinase McsB in vivo. Exhibits almost no activity against pTyr peptides. Protein arginine phosphorylation has a physiologically important role and is involved in the regulation of many critical cellular processes, such as protein homeostasis, motility, competence, and stringent and stress responses, by regulating gene expression and protein activity. H2O + N(omega)-phospho-L-arginyl-[protein] = L-arginyl-[protein] + phosphate Irreversibly inhibited by the synthetic inhibitor cyc-SeCN-amidine, which inactivates the enzyme by inducing disulfide bond formation between the two active site cysteine residues Cys-9 and Cys-14. kcat is 1.12 sec(-1) with pNPP as substrate (at 25 degrees Celsius and pH 7.6) (PubMed:23838530) and 3.2 sec(-1) with pNPP as substrate (at 40 degrees Celsius and pH 8.0) (PubMed:23770242). pNPP is a phospho-tyrosine mimicking compound. Is present in solution as a mixture of monomers, dimers and higher order oligomers (trimers and tetramers). An engineered YwlE Ala-9 mutant can be used as a phosphatase trap that efficiently captures arginine-phosphorylated proteins but cannot hydrolyze the captured substrates, thus facilitating identification of phosphoarginine sites in the large pool of cellular protein modifications. Therefore, this novel tool for the selective enrichment and subsequent MS analysis of arginine phosphorylation should facilitate the investigation of this highly overlooked protein modification, in particular in eukaryotic samples. Belongs to the low molecular weight phosphotyrosine protein phosphatase family.