WHOIS / RDAP

What it does: looks up WHO is behind a domain, IP address, or network — the registration record. RDAP is the modern, structured replacement for classic WHOIS. It's the "who owns this / who do I contact about it?" tool.

What you need: a domain (example.com), an IP address, or an ASN (e.g. AS15169).

Safe to run: yes — a public read-only lookup.

What to expect / reading results: you get the registrant/owner (often a privacy-shielded proxy for domains), the responsible organization for an IP/ASN, the status, and key dates (created/updated/expires). Common uses: identify which provider owns an unfamiliar address, or check whether a domain has lapsed or is about to expire.