When WebsiteDown checks a domain, one of the first things we report is the HTTP status code. That three-digit number carries more information than most people realize. Here is what each class of response means in practical terms.
2xx — Success
A 200 OK response means the server received the request and returned a response without errors. This is the expected state for a healthy website.
204 No Content is sometimes returned by APIs — a valid response indicating the request succeeded but there is no content to return. For a browser-facing URL, this often indicates a misconfiguration.
A 2xx response from a monitoring check means the server is reachable and functioning at the network layer. It does not guarantee the application is working correctly — see content validation.
3xx — Redirects
301 and 302 responses are redirects. They are normal and expected — most sites redirect HTTP to HTTPS, or www to non-www. Monitoring tools should follow redirects and report the final status code.
A redirect loop (a site redirecting to itself infinitely) causes a browser to show an error after following some number of redirects. A monitor following redirects will eventually timeout or hit a redirect limit, reporting an error even though the server is technically responding.
4xx — Client errors
400 Bad Request means the server understood the request but rejected it, usually because it was malformed.
401 and 403 mean the resource requires authentication or the client is not authorized. Many monitoring tools get 403 responses when checking sites that block data center IP ranges — this is the site working correctly, not failing.
404 Not Found is often misread as a site being down. A 404 means the server is running and responding — it just did not find the specific resource requested. The server is up; the URL might be wrong.
429 Too Many Requests means the server is rate-limiting the client. For monitoring tools hitting the same URL repeatedly, this is increasingly common.
5xx — Server errors
This is the class of errors that indicates actual server-side failure.
500 Internal Server Error is the generic catch-all for when something unexpected went wrong on the server. Deployment errors, unhandled exceptions, and database failures often produce 500s.
502 Bad Gateway and 503 Service Unavailable typically mean a proxy or load balancer received no valid response from the upstream application server. This is what you see when the application is down but the web server layer is still running. 503 in particular is the canonical "site is down" response.
504 Gateway Timeout means the upstream server did not respond in time. This often indicates the application is overloaded or a database query is hanging.
Timeouts — no status code at all
A timeout is different from any of the above: the server never responded at all within the allowed time window. This typically means the server is completely unreachable — the network path is broken, the server process has crashed, or the machine is down.
Timeouts are the most severe signal. A 503 means the server is struggling but alive. A timeout means there is no server at the other end of the request.