Simplicity wins again. Much as there are more RESTful APIs than SOAP, XML-RPC or other protocols, JSON is gaining ground on the old favorite, XML. Last fall we said JSON is the developer's choice and therefore it's becoming the API provider's choice, too. XML still wins overall, but more new APIs use JSON than XML. Of APIs we've seen in 2011, 20% only use JSON, meaning 1 in 5 are saying goodbye to XML.
JSON, without opening and closing tags, is lighter weight, which both developers and providers appreciate. There also isn't the overhead of namespaces and schemas
The trend in our API directory is quite apparent: XML is on the decline. But is that a good thing? Enterprises may prefer XML because they have the tools in place to support it. Also, much of the reason XML is complex is that it's trying to solve complex problems of data interchange by providing a meta language to describe the data.
As JSON gains wider adoption, it will face some of the same issues XML tackled over the last decade. The JSON Schema project is one example of standardization happening within JSON. Will developers continue to choose a more complex JSON? Will providers return to XML for the tools it has to support complexity?