Online and HTTP status
What: We request your home page the way a browser does and record the status code.
Why: Anything but a 2xx is a visitor turned away. A 5xx is an outage; a 4xx is a misconfiguration.
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Nine checks in twenty seconds, scored out of 100: is it online, how fast, is the certificate about to expire, is the domain, does DNS resolve, how many redirects, which security headers are missing. No account, no install.
What is checked, and why it matters
Response time
What: Time to first byte and total time, from Frankfurt.
Why: Over 800 ms to the first byte and visitors feel it; over two seconds and search engines do.
HTTPS and certificate
What: Whether the site is served over HTTPS, and the certificate's issuer, validity and days remaining, verified like a browser would.
Why: An expired or untrusted certificate shows a full-page warning. Most expire on a 90-day cycle nobody is watching.
Domain expiry
What: The registrable domain's expiry date and registrar, from RDAP or WHOIS.
Why: A lapsed domain takes the site, the mail and the API down at once, and getting it back can take days.
DNS and IPv6
What: The addresses the name resolves to, IPv4 and IPv6.
Why: No record means no site. No IPv6 means a growing share of mobile traffic reaches you through translation.
Redirects
What: Every hop from the address you typed to the page that finally answers.
Why: Three hops is three round trips before a visitor sees anything, and a chain that changes is a chain that breaks.
Security headers
What: Strict-Transport-Security, Content-Security-Policy, X-Content-Type-Options, X-Frame-Options, Referrer-Policy, Permissions-Policy.
Why: Six response headers stand between your visitors and the most common attacks on a site; most sites send none of them.
Page size and compression
What: Bytes on the wire and whether the response was compressed.
Why: An uncompressed page is three to five times larger than it needs to be, on every visit.
robots.txt and sitemap
What: Whether the two files search engines look for first exist.
Why: Without them, crawlers guess; with them, they find what you want found.
One check tells you today. Monitoring tells you the day it changes.
Add the same address as a monitor and ServerInspector checks it every five minutes on the free plan, every minute on Pro, and emails you the moment it stops answering, the week before the certificate expires, and a month before the domain does.