Free Online Network & IP Tools
Check your public IP and user agent, run a DNS record lookup and calculate IPv4 or IPv6 subnets, CIDR ranges and host counts - free, no signup.
See your public IP address, approximate location, ISP, browser and user agent exactly as a web server sees them. Free instant IP lookup tool.
Look up A, AAAA, MX, TXT, NS, CNAME and SOA records for any domain and see how DNS resolution actually works, step by step. Free online tool.
Calculate network address, broadcast, usable host range, subnet mask and wildcard from any IPv4 CIDR block. Free subnetting calculator with examples.
Expand and compress IPv6 addresses, calculate prefix ranges and host counts, and identify address scope and type. Free IPv6 CIDR calculator.
Four tools, two audiences
The IP and user agent checker answers a question anybody might have: what does a website see when I visit it? The DNS lookup, IPv4 subnet calculator and IPv6 subnet calculator are working tools for people who administer networks and domains.
What your IP address does and does not reveal
Every site you visit sees your public IP because it has to — that is the return address the response is sent to. From it a site can derive a rough geographic location, usually accurate to the city or region, and identify your ISP. What it cannot derive is your name, your street address or your identity; that mapping exists only with your ISP and generally requires legal process to obtain.
The user agent string that travels alongside it is often more identifying than the IP. Combined with screen resolution, installed fonts, timezone and canvas rendering behaviour, it forms a browser fingerprint that can be distinctive enough to track a visitor across sites without any cookie at all. The IP checker shows you the headers your browser is actually sending so you can see the surface for yourself.
DNS: what each record type is for
A domain name resolves through a chain — root servers, then the top-level domain's servers, then the domain's own authoritative nameservers — and the answer is cached at every step for the length of its TTL. That caching is why a DNS change is not instant, and why "it works for me" and "it is still broken for me" can both be true for hours.
| Record | Answers | Commonly checked when |
|---|---|---|
| A / AAAA | Which IPv4 / IPv6 address serves this name | A site is not loading after a migration |
| CNAME | This name is an alias for that name | A subdomain points at a SaaS provider |
| MX | Which servers accept mail for this domain | Email is bouncing |
| TXT | Arbitrary text: SPF, DKIM, DMARC, domain verification | Mail lands in spam, or a service will not verify ownership |
| NS | Which nameservers are authoritative | A registrar transfer is in progress |
| SOA | Zone metadata: serial, refresh, TTLs | Diagnosing propagation and secondary sync |
A practical tip for migrations: lower the TTL on the records you are about to change to 300 seconds at least a day before the change. If you lower it at the same time as the change, the old long TTL is already cached and you gain nothing.
Subnetting without the arithmetic
CIDR notation writes a network as an address plus a prefix length, like 192.168.10.0/24. The prefix is how many leading bits identify the network; the rest identify hosts within it. A /24 fixes 24 bits, leaving 8 for hosts: 256 addresses, of which 254 are usable because the first is the network address and the last is the broadcast address.
| Prefix | Subnet mask | Total addresses | Usable hosts |
|---|---|---|---|
| /30 | 255.255.255.252 | 4 | 2 |
| /29 | 255.255.255.248 | 8 | 6 |
| /28 | 255.255.255.240 | 16 | 14 |
| /27 | 255.255.255.224 | 32 | 30 |
| /26 | 255.255.255.192 | 64 | 62 |
| /25 | 255.255.255.128 | 128 | 126 |
| /24 | 255.255.255.0 | 256 | 254 |
| /16 | 255.255.0.0 | 65,536 | 65,534 |
Each step down the prefix doubles the size. The IPv4 calculator also gives you the wildcard mask, which is the mask inverted and is what Cisco access control lists and OSPF configurations expect — a frequent source of confusion for people who assume ACLs take a normal subnet mask.
IPv6 is different in ways that matter
IPv6 has no broadcast address and no concept of reserving the first and last address, so every address in a prefix is usable. A /64 is the standard subnet size for a LAN and contains 18 quintillion addresses — you do not subnet below it, because stateless address autoconfiguration depends on that boundary. Addresses are also written with two shortening rules: leading zeros in a group are dropped, and one run of all-zero groups collapses to ::, which may appear only once in an address. The IPv6 calculator expands and compresses addresses so you can check that a shortened form is the one you meant.