All-Images uses conventional HTTP response codes to indicate the success or failure of an API request.
As a general rule:
Codes in the 2xx range indicate success.
Codes in the 4xx range indicate incorrect or incomplete parameters (e.g. a required parameter was omitted, or an operation failed with a 3rd party, etc.).
Codes in the 5xx range indicate an error with All-Images's servers.
All-Images also outputs an error message and an error code formatted in JSON: