Important HTTP Response Codes

Code	Meaning	Message
200	OK	Success!
304	Not Modified	There was no new data to return.
400	Bad Request	The request was invalid. An accompanying error message will explain why. This is the status code will be returned during rate limiting.
401	Unauthorized	Authentication credentials were missing or incorrect.
403	Forbidden	The request is understood, but it has been refused. An accompanying error message will explain why. This code is used when requests are being denied due to update limits.
404	Not Found	The URI requested is invalid or the resource requested, such as a user, does not exists.
406	Not Acceptable	Returned by the Search API when an invalid format is specified in the request.
420	Enhance Your Calm	Returned by the Search and Trends API when you are being rate limited.
500	Internal Server Error	Something is broken. Please post to the group so the Our Servers team can investigate.
502	Bad Gateway	Our Servers are down or being upgraded.
503	Service Unavailable	Our Servers are up, but overloaded with requests. Try again later.
504	Gateway timeout	Our servers are up, but the request couldn't be serviced due to some failure within our stack. Try again later.