[morelisp]

I've used both Problem Details and JSONAPI errors[0] which are basically the same idea (and I've used them plenty outside of JSONAPI-proper APIs). In both cases if you have a decent error-handling middleware there should be not much difference than outputting any other kind of errors.

One thing to keep in mind re. "maybe-json-maybe-plaintext-maybe-empty" responses is that the more complex your errors, the more likely the error handling encounters an error. If you're trying to send back some JSON or XML but it fails it's usually better to at least shove out a line of plain text and hope it reaches a human than to mask the real error with a second fallback in the "right format" but with unhelpful fixed content.

[0] https://jsonapi.org/format/#error-objects