Just thinking of the failure of XSD, WSDL, and other XML formats back in the day. It’s amusing to think that many of the difficulties that came from working in these formats were waved away with sayings like “ah, tooling will help you there,” or “of course there’s going to be a GUI editor for it.”

Compare that to a format like Protobuf. Sure, there are tools to generate the code, but it assumes the source will be written by humans using nothing more than a text editor.

That might be why formats like RSS and XML-RPC survived. They’re super simple to understand as they are. For all the others, it might be that if you feel your text format depends on tools to author it, it’s too complicated.