We also keep a list of HTTP status code errors (4xx and 5xx) along with some tips on how to fix them.
HTTP Status Code Categories
As you can see below, HTTP status codes are three-digit integers. The very first digit is used to identify the code within a specific category—one of these five:
1XX: Informational—the request was accepted or the process is continuing. 2XX: Confirms that the action completed successfully or was understood. 3XX: Redirection—something else needs to take place in order to complete the request. 4XX: Client error that indicates that the request can’t complete or contains the wrong syntax. 5XX: Server error that indicates that the server failed to complete a request that was supposedly valid.
Applications that understand HTTP status codes don’t have to know all these codes, which means an unknown code also has an unknown HTTP reason phrase, which won’t give the user much information. However, these HTTP applications do have to understand the categories or classes as we’ve described them above. If the software doesn’t know what the specific code means, it can at the very least identify the class. For example, if a 490 status code is unknown to the application, it can treat it as a 400 because it’s in the same category, and can then assume there’s something wrong with the client request.
HTTP Status Lines (HTTP Status Codes + HTTP Reason Phrases)
Unofficial HTTP Status Lines
The HTTP status lines below might be used by some third-party services as error responses, but they are not specified by any RFC.
