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HTTP status codes are standard response codes that web servers use to indicate whether a specific HTTP request was successfully completed. They are grouped into five categories: 1xx (informational), 2xx (success), 3xx (redirection), 4xx (client error), and 5xx (server error).
200 OK is the most common successful response. 404 Not Found is the most widely recognized error code. 500 Internal Server Error is the most common server-side error. 301 and 302 are the most common redirect codes.
301 Moved Permanently means the resource has been permanently moved to a new URL. Search engines will update their index to the new URL. 302 Found means a temporary redirect — search engines keep the original URL and do not transfer ranking.
403 Forbidden means the server understands the request but refuses to authorize it. Check: file/directory permissions, .htaccess or nginx configuration, IP whitelist/blacklist rules, authentication requirements, or WAF/firewall blocks.
401 Unauthorized means authentication is required and has failed or not been provided — the client can retry with credentials. 403 Forbidden means the server refuses to authorize the request regardless of authentication — retrying with credentials won't help.