Updated 25 October 2026 · By the Upcertain team
1. Rule out your own connection
- Open another site you know works.
- Try the site on mobile data instead of Wi-Fi, or from a different network.
- Try a private window, which skips your cache, cookies and most extensions.
2. Check the site's status page
Many services publish one, often at status.<domain>. If they report an incident, you have your answer and their timeline.
3. Ask the network directly
# Does the name resolve?
dig +short example.com
# Does the server answer, and with what status?
curl -sS -o /dev/null -w "%{http_code} in %{time_total}s\n" https://example.com
# Is the certificate valid, and until when?
echo | openssl s_client -connect example.com:443 -servername example.com 2>/dev/null | openssl x509 -noout -dates| What you see | Likely meaning |
|---|---|
dig prints nothing | DNS problem: the name does not resolve |
curl times out | Server or network down, or a firewall blocking you |
curl prints 5xx | The server answers but the application is failing |
curl prints 200 but the page is broken | A front-end or content problem |
| Certificate dates in the past | An expired certificate: browsers show a warning |
Common causes, quickest to check first
- A deploy in the last hour: roll it back or check its logs.
- The hosting provider or CDN: check their status pages.
- DNS: a changed or expired record, or an expired domain.
- The certificate: expired, or not covering the name you visit.
- Resources: a full disk, an exhausted database connection pool or a memory limit.
4. Check from somewhere else
Ask a colleague in another place or network to load the site, or run the curl command from a server you have elsewhere. If it works there and not for you, the problem is between you and the site.
If it is your site
- Check your hosting provider's and CDN's status pages.
- Look at the last deploy: roll it back if the timing matches.
- Check the certificate and the domain's DNS records.
- Post a short update on your status page so customers stop wondering.
Why a one-off check is not monitoring
Checking by hand tells you about now. It does not tell you when the problem started, whether it happened last night while you slept, or that the certificate expires next week. Monitoring checks on a schedule, confirms failures, alerts the right people and keeps the history. See what uptime monitoring is.
Questions
Can a site be down only in some countries?
Yes. A CDN or network problem can affect one region while the rest of the world loads the site normally.
Why does a site work on my phone but not my laptop?
Usually a local cause: a DNS cache, a browser extension, a VPN or a network filter. Try a private window, flush the DNS cache or switch networks.
What does a 503 error mean?
The server is reachable but cannot handle the request right now, often during a deploy, an overload or maintenance.