When you test your layer at the "Test your layer" page and something is wrong in the response from the server, the error message most of the time either doesn't make sense, or it makes perfect sense and is plainly wrong.

Just an example: I'm trying to build an API5-compliant layer, and I get this message:

• response code : 200
  error validating provider response - Traceback (most recent call last): File "/var/www/layar.com/app/api/handlers/api_layer/mainproxy.py", line 85, in validate_response data = validator.validate(response_as_dict, schema) File "/var/www/layar.com/app/api/jsontransmogrifier.py", line 560, in validate raise ValidationError(message=", ".join(self.errors), errors=self.errors) ValidationError: Missing value ''contentType'' in response: , Failed to validate field 'hotspots' list schema: "Missing value ''contentType'' in response: "
  JSON parse error( most likely)!, validate your response at http://www.jsonlint.com/
  Missing value ''contentType'' in response: , Failed to validate field 'hotspots' list schema: "Missing value ''contentType'' in response: "
  Error: No content available

This seems to indicate that there is a missing "contentType" field, but according to API 5 documentation, the hotspot has no mandatory (nor even optional) contentType field. The contentType field exists in the hotspot object only in API6; in API 5 it exists in the action object, but in my case there is no action at all. I'm sure there's something wrong in my server response but this error message is inconsistent, so either it or the api documentation is wrong.

ANOTHER example is if you happen to pass the lat and long fields of the anchor as strings rather than as floats. It took me ages to figure out. You get a completely screwed up error message that tells something about an int and shows values that are not even in the response.