They give a good rationale for supporting PATCH, but not for omitting PUT. Not supporting PUT is absolutely a mistake, especially with a schema-less backend. Being unable to PUT means being unable to set a property as undefined (by PUTting a complete version of the resource without that property). The usual approach with PATCH is to set it to None/null, but then the property is still defined as None instead of removed. (Or, some APIs will remove a property with a None value, but then it is undefined instead of being set to None.) A small but potentially important semantic distinction.