Not Modified
The resource hasn't changed since your last request. The server is telling the client to use its cached copy. This is a good thing — it means caching is working.
COMMON CAUSES
HOW TO FIX IT
What this means for monitoring
If your monitor sends caching headers (ETag, If-Modified-Since), you might get 304s instead of 200s. Most monitoring tools don't send these.
Related status codes
3xx Redirection
The resource has permanently moved to a new URL. Search engines transfer ranking to the new URL. Browsers cache this aggressively — if you set one by mistake, it can be hard to undo.
The resource is temporarily at a different URL. The client should continue using the original URL for future requests. Often used for login redirects and temporary maintenance pages.
The response to your request is at a different URL, and you should use GET to retrieve it. Common after a POST — the server is saying "the thing you created is over here."
Like 302 but stricter — the client must use the same HTTP method for the redirected request. A POST stays a POST. 302 technically allows the method to change.
Like 301 but stricter — the client must use the same HTTP method. A POST to the old URL should POST to the new URL too.
Get alerted when your endpoints return unexpected status codes.
Larm checks your HTTP endpoints from multiple global locations and alerts you when they return status codes outside your expected range.