What HTTP Status Codes Should Programmers be Concerned With?

Question

So, if you look at the List of HTTP Status Codes, there are probably a number of them that would be useful while programming. The server might handle some things, like protocols

Answer 1

Quickly going through that list (of status codes), here are those I often use (I am doing PHP web-development as my job) :

• 200 OK : almost always sent by Apache
• 301 Moved Permanently : generally sent by me (or by Apache, when using rewrite-rules)
• 302 Found : generally sent by me (or by Apache, when using rewrite-rules)
• 304 Not Modified : generally sent by Apache (or a reverse proxy in front of it)
• 401 Unauthorized : generally sent by Apache
• 403 Forbidden : generally sent by Apache
• 404 Not Found : sent both by Apache and me -- depending on the situations
• 410 Gone : generally sent by me
• 500 Internal Server Error : sent both by Apache and me ; that's the one I generally use when there's a "technical" error -- even if it should never happen ^^

And here are those I could use (especially if doing REST) :

• 201 Created
• 400 Bad Request
• 402 Payment Required
• 405 Method Not Allowed
• 501 Not Implemented
• 503 Service Unavailable