HTTP Status codes are issued by a server in response to to the client's request. These status codes (as part of the response message) helps to inform clients around the result of their REST API request.
All HTTP response status codes are separated into five classes (or categories). The first digit of the status code defines the class of response.
The request was received, continuing process
The request was successfully received, understood, and accepted
Further action needs to be taken in order to complete the request
The request contains bad syntax or cannot be fulfilled
The server failed to fulfill an apparently valid request
Following are some commonly used status codes.