Visual studio does schema validation for JSON and gives errors inline. There is a big list of supported schemas built in and you can define your own. Never actually looked at the format personally.

Json schema is what vscode uses. It’s a standard nowadays. Just as effective as XMLSchema.

https://jsonschema.net/

http://www.schemastore.org/json/

While I generally agree, I'm not sure maven's pom.xml (aka porn.xml), of all things, is a paragon of good markup design ;) For one, maven actively forbids/rejects use of ordinary XML entity references, and invents its own text expansion instead (so strictly speaking pom.xml isn't even XML proper). Then using XML for a relatively simple EAV format seems like overkill. But yeah, over a decade ago the maven developers had great plans to open up the format for alternative serializations/DSLs; thankfully they didn't, if only because they realized it isn't worth the maintenance effort. I'll add that a format for describing software builds is probably the wrong place to let a thousand blossoms bloom, something that you realize soon enough if you've worked as freelancer in Java-ish project's for any amount of time, and where every other project is feeling the urge to use the oh-so-great gradle as an alternative to pom.xml.

My comment was only aimed at service payload serialization; as to whether markup makes for a good config file format, I'm not entirely sure. It certainly is better than inventing an ad-hoc format IMO, but OTOH there are a couple of not-quite-SGML/XML config formats such as Apache's httpd.conf, or in fact maven's that just give XML/SGML a bad name IMHO, because they generally inherit the downsides of markup without bringing its benefits (such as being able to assemble a configuration from fragments using regular entity expansion).

pom.xml is not a great example of proper XML use. For example maven should utilize additional namespaces for plugin configurations, but it does not.