HTTP Status Codes
1xx — Informational
100 Continue, 101 Switching Protocols, 102 Processing
200 OK
Request succeeded — the standard success response
201 Created
Resource created successfully (POST/PUT)
204 No Content
Success but no body returned (DELETE)
301 Moved Permanently
Resource permanently moved — update bookmarks, SEO passes
302 Found
Temporary redirect — client should keep using original URL
304 Not Modified
Cached version is still valid (ETag/If-Modified-Since)
400 Bad Request
Malformed syntax, invalid parameters, or missing fields
401 Unauthorized
Authentication required — missing or invalid credentials
403 Forbidden
Authenticated but not authorized for this resource
404 Not Found
Resource does not exist at this URL
409 Conflict
Request conflicts with current state (concurrent edits, duplicate)
429 Too Many Requests
Rate limit exceeded — check Retry-After header
500 Internal Server Error
Unhandled server exception — generic catch-all
502 Bad Gateway
Upstream server returned an invalid response
503 Service Unavailable
Server overloaded or in maintenance — retry later
504 Gateway Timeout
Upstream server did not respond in time