Who runs it
Site Checker Lab is built and maintained by DEV2REV, a small software company in Porto, Portugal. It is an independent site, not owned by a hosting company, registrar or monitoring service.
Why it exists
When a site breaks, the first questions are always the same. Is it down for everyone? Did the certificate expire? Did the domain lapse? Has the DNS change reached everyone yet? This site answers them in one report, says plainly when it can't tell, and never keeps the full addresses people check.
How the checks work
Every check runs on our own servers, from one region, US East in New York, at launch. Requests identify themselves with a user agent that names this site.
- Reachability: one request from each region to the final address, recording the status code and the time to the first byte. The page body is never read.
- Redirects: we start at
http://and the hostname and follow up to 10 redirects, checking each new address before we connect. - SSL: a secure connection to port 443, reading the certificate, its chain and the names it covers.
- DNS: A, AAAA, CNAME, MX, NS and TXT records from a public resolver. DNS propagation asks several public resolvers at once.
- Domain expiry and availability: the registry's public RDAP record, found through IANA's list of registries.
Private, internal and reserved addresses are refused before any request is made, and so is any name that points to one.
How verdicts are decided
- Down only when two or more regions all get a clear error: a refused connection, a failed secure connection, a 5xx error, or a name that doesn't exist.
- Not responding when our only region gets a clear error. One region is not enough to call a site down.
- Couldn't check when requests time out or are cut off. Many sites block automated checks, so silence is not proof of anything.
- Certificates and domains get a warning under 30 days left and are marked as a problem under 7.
What the checks can't see
- Pages behind a login, and anything a site only shows to real browsers
- Problems on one visitor's own network, browser or DNS cache
- Regions we don't check from yet
Results show what our servers saw at the moment of the check. Run it again for a fresh answer.
How the site is paid for
The site is free and shows ads from Google AdSense. Some links to monitoring services and registrars are affiliate links, which are always labelled. Neither advertisers nor affiliates have any say over the checks or their results. Details are in the privacy policy and affiliate disclosure.
Found a mistake?
If a result looks wrong, email hello@sitecheckerlab.com or use the contact page. Last reviewed November 2026.