IP address lookup
What an address is, what it is for, which registry it was allocated to, and what it calls itself in reverse DNS.
How to read this
Public, private, and the ones in between
Most addresses fall into one of a handful of reserved blocks with a specific job. Private ranges are reusable inside any network and never route publicly. Carrier-grade NAT space, 100.64.0.0/10, belongs to your ISP and means you are sharing a public address with other customers — port forwarding will not work and no inbound connection will reach you. A 169.254 address means DHCP failed and the machine gave up and named itself. Knowing which block an address sits in usually answers the question faster than any lookup.
Reverse DNS is a claim, not a proof
A PTR record is set by whoever controls the address block, so it is a reasonable signal of who operates an address and a poor one for anything security-related. Its real use is mail: many receiving servers reject or downgrade mail from an address whose reverse DNS is missing, or does not match the name the server introduces itself with. If mail from your own server is landing in spam, this is one of the first three things to check.
Why there is no city on this page
Because the databases that would put one there are licensed for non-commercial use, and a company website is commercial use. A licence breach is not a thing to discover later, so this tool reports what the public registries and DNS can establish rather than pretending to precision it has not paid for. The licence-clean route is a self-hosted GeoLite2 database with visible attribution, which is on the list.
Doing this for a business rather than for yourself? Networking.
The other tools
Subnet Calculator
Ranges, masks and host counts for IPv4 and IPv6. Runs entirely in your browser — nothing you type is sent anywhere.
DNS Lookup
The same question asked of eight public resolvers at once, so you can see where a change has propagated and where it has not.
SSL Checker
Expiry, issuer, the names it covers, the chain, the protocol and the cipher — and plain sentences about anything that is wrong.