Yes but once the json has been validated once at runtime, you know it's safe for the rest of your program to use. Whereas in a dynamic language (even an immuta

Yes but once the json has been validated once at runtime, you know it's safe for the rest of your program to use. Whereas in a dynamic language (even an immutable one), your data could be mutated during program runtime and no longer conform to the type you expected. Yes you could re-validate it everywhere, but that requires you to exercise every code path when testing at runtime to find bugs. I think the general argument that "You can't static type everything (like your API dependencies), so there's no point in doing it all" isn't a very solid one.