List of key HTTP status codes and their explanations

HTTP Status Codes and Their Meanings.

1. 
   200 - Success: The server successfully processed the request.


2. 
   201 - Created: The request has been fulfilled, resulting in the creation of a new resource.


3. 
   300 - Level status codes: These status codes are all about redirecting.


4. 
   301 - Moved Permanently: The page at a certain URL has been permanently moved to a new URL.


5. 
   302 - Found: The page is at a new URL, but this is a temporary change.


6. 
   304 - Not Modified: The resource being requested has not changed (used for caching).


7. 
   400 - Bad Request: The server cannot process the request due to a client error.


8. 
   401 - Unauthorized: The client must authenticate itself to get the requested response.


9. 
   402 - Payment Required: Payment is required before the server can process the request.


10. 
    403 - Forbidden: The client does not have permission to access the content.


11. 
    404 - Not Found: The server cannot find the requested resource.


12. 
    500 - Internal Server Error: The server encountered a situation it doesn't know how to handle.


13. 
    501 - Not Implemented: The server does not recognize or support the request method.


14. 
    503 - Service Unavailable: The server is not ready to handle the request.


15. 
    504 - Gateway Timeout: The server, while acting as a gateway or proxy, did not receive a timely response from an upstream server.

The document also provides a summary, highlighting that HTTP status codes range from success (200, 201) to various types of errors (400-series and 500-series).