Check from somewhere that is not your network
Open the site, then check it on DownSpotter (or another independent monitor you trust). Compare the two. If both fail, gather the error type: timeout, DNS, certificate, or an HTTP 5xx. That tells you what to do next.
Read the HTTP status
A 200 means some server answered successfully. A 403 or 401 still means the site is up — it is refusing or asking for auth. 502 and 503 usually mean a proxy or application is in trouble. Timeouts and DNS errors mean we never got a useful HTTP answer.
Don’t use an unrestricted proxy
A website checker should never fetch arbitrary URLs into private networks. If a tool lets you request internal IPs, it is unsafe. DownSpotter only allows public HTTP and HTTPS and validates every DNS answer and redirect.