A JSON-Schema is a great thing. You are able to validate your document without doing a lot of work. When such a schema file exists it is the easiest way to see if the content of your document is correct.
Unfortunately in most cases such a document does not exists. That often is because the creation of a schema file can be very extensive. But what to do if such a file does not exist? From our experience this doesn’t matter. In most cases it is enough to check if a JSON document is well formed. If a document is syntactically correct there is a big chance that the content is also correct. If there is a bug in the application there is mostly a broken output.