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From the blog

Why Does Ping Fail?

Five real causes of a ping timeout, and how to confirm whether a host is actually down.

Understanding Traceroute

How traceroute works, how to read every hop, and what timeouts and latency jumps mean.

SSL Certificate Expired?

What causes it, how to renew fast, and how to stop it from happening again.

What each check does

Ping

Sends small packets to a host and measures how long they take to come back. Useful for spotting outages or high latency.

DNS Lookup

Shows how a domain resolves and which records are attached. Usually the first thing to check when a domain is pointed wrong.

Traceroute

Maps the path a request takes across the internet, hop by hop. Useful for diagnosing slow routes or blocked regions.

WHOIS

Looks up who owns a domain, when it was registered, and when it expires.

SSL check

Fetches a site's certificate to confirm it's valid, trusted, and not about to expire.

Security Headers New

Checks for the handful of security-related HTTP headers browsers look for, and reports which ones are set.

Blacklists New

Looks up a host's IPv4 address against public spam and abuse blacklists. This is the same signal mail servers use to decide whether to bounce a message.

DNS Propagation New

Queries a domain against several major public resolvers side by side, to check whether a DNS change has propagated everywhere yet.