I have been using XML for data transmission and for data specification since 2000. What I like most of XML and XSD is that I can define several namespaces for different fields, this way, whenever I get a tag (e.g. ), it has implicity the scope of such tag, there are no doubt whether the belongs to a scope or to another because it comes with its namespace (e.g. can be "books" or "pencils"). If you define good XSD files, the XML will be parsed and be XSD-compliant with any language (C#, Java, Python...), serializing the XML documents into objects and viceversa. [There are other great things of XML that I really like, but it is not the aim of this discussion.] When I have to deal with personal data or some data regarding "money" (bills, business, purchases...) I always use XSD because I want to map the correct data into the correct field. For other, not sensible, data I use JSON. Important note: Beware of namespaces, the most common error when parsing is when namespaces are in-lined. Some XML are produced badly and the receiver launches weird errors that make developers eventually hate XML. I think that it can be the reason for your intolerance this morning :laugh: For data transmission, if the bandwidth is a problem, you can use EXI (Efficient XML Interchange (EXI) Format 1.0 (Second Edition)), which is better than compressing (gzip) JSON. But make sure that sender and receiver can manage EXI. To sum up, JSON is very easy, but I still prefer XML/XSD for important data or data that must be signed, verified or checked.