You just use the validation rules normally.
#Validate JSON body, POST request?
long solstice
faint dawn
But I did that. There are some levels, like article.description, but I tried a simple field name without periods too (and set it as required). The result was the same, the validation errored out with "The field is required".
When I stepped through the code I also tried running request()->input(). My querystring parameter was there, but nothing else.. So I kind of get the impression that the JSON body isn't decoded. Perhaps I've written the validation rules correctly but something else is causing Laravel to ignore the JSON?