Agree with @odyniec - errors do not represent a resource. I would question your need for them in responses - this to me feels like an anti-pattern. Considering errors should be part of a 4xx or 5xx response, the status code should be enough to let you know.
Also stipulating casing in API responses... let's leave style out of such tips and equations (they serve nothing other than to start debates). This point should have been in personal preferences.
Some good general points here which I like.
Agree with @odyniec - errors do not represent a resource. I would question your need for them in responses - this to me feels like an anti-pattern. Considering errors should be part of a 4xx or 5xx response, the status code should be enough to let you know.
Also stipulating casing in API responses... let's leave style out of such tips and equations (they serve nothing other than to start debates). This point should have been in personal preferences.