HTTP Status Codes: The Essential Ones

Every HTTP response carries a three-digit status code that signals the success or failure of a request.

2xx — success

• 200 OK: everything fine.
• 201 Created: resource created (POST).
• 204 No Content: successful, but no response data.

3xx — redirection

• 301 Moved Permanently: permanently moved.
• 302 Found: temporarily elsewhere.
• 304 Not Modified: cache is current.

4xx — client errors

• 400 Bad Request: malformed request.
• 401 Unauthorized: authentication missing.
• 403 Forbidden: forbidden even with login.
• 404 Not Found: page does not exist.
• 429 Too Many Requests: rate limit reached.

5xx — server errors

• 500 Internal Server Error: generic error.
• 502 Bad Gateway: upstream not responding.
• 503 Service Unavailable: overload/maintenance.

See also: Programming.