Does this call an external API?

No. There are no fetch requests; everything runs in your browser.

Why doesn’t it show my city or ISP?

That would require a database or network lookup. This page is a reference and classifier only.

New

IP Address Reference

Runs in browser

Learn how IPv4 and IPv6 addresses work: private vs public ranges, loopback, subnet masks, and CIDR — with a client-side checker that classifies any address you type (no external APIs).

Try an address

Type any IPv4 or IPv6 address. Classification runs entirely in your browser — no servers, no geolocation, no external requests.

IP address

Public (IPV4) — globally routable on the internet (subject to your network’s actual routing and firewall rules).

What is an IP address?

An Internet Protocol (IP) address is a numeric label assigned to a device on a network. It identifies the host so routers can deliver packets. Most traffic you think of uses either IPv4 (32-bit, dotted decimal) or IPv6 (128-bit, hexadecimal groups).

IPv4 vs IPv6

IPv4 uses four bytes, written as four decimal numbers from 0–255, e.g. 203.0.113.42. There are not enough unique IPv4 addresses for every device worldwide, so networks use NAT and private ranges.

IPv6 uses 128 bits, written as up to eight groups of four hex digits, e.g. 2001:0db8:85a3::8a2e:0370:7334 (leading zeros can be omitted; a single :: can replace a run of zero groups).

Public vs private ranges (IPv4)

On the public internet, routers expect “global” addresses. Certain ranges are reserved for use inside private networks (LANs). Those addresses are not globally unique and are not routed as public endpoints on the internet.

Range (CIDR)	Typical use
10.0.0.0/8	Private — large org / home LANs (10.x.x.x)
172.16.0.0/12	Private — 172.16.x.x through 172.31.x.x
192.168.0.0/16	Private — common home routers (192.168.x.x)
Everything else (valid unicast)	Treated as public for this guide’s classifier

This page’s interactive check marks 10/8, 172.16/12, and 192.168/16 as private. Loopback and special addresses below are classified separately.

Special IPv4 addresses

127.0.0.1 (and all of 127.0.0.0/8) — loopback; refers to the local machine.
0.0.0.0 — unspecified / “any” in some APIs; not a normal destination.
255.255.255.255 — limited broadcast on the local subnet.

What is a subnet mask?

A subnet mask (often written like 255.255.255.0) tells a device which part of an IPv4 address is the network prefix and which part identifies the host. Where the mask has binary 1s, those bits belong to the network; where it has 0s, they belong to the host. Masks are how routers know which addresses are on the same LAN versus reachable via a gateway.

CIDR notation

Classless Inter-Domain Routing (CIDR) writes a network as an address followed by a slash and a prefix length: the number of leading bits that are fixed for the network. Example: 192.168.1.0/24 means the first 24 bits are the network (equivalent to mask 255.255.255.0), leaving 8 bits for hosts on that subnet. Larger numbers after the slash mean a smaller network (fewer host bits).

How to use

Classify an address
Type an IPv4 or IPv6 value in the box; the badge updates instantly with public, private, loopback, or special.
Read the sections
Scroll through IPv4 vs IPv6, the private-range table, specials, masks, and CIDR.
Stay offline
No geolocation and no network requests — only local string checks.

Examples

Home router
Typical LAN address.
Input
```
192.168.1.1
```
Output
```
Private
```
Loopback
Localhost.
Input
```
127.0.0.1
```
Output
```
Loopback
```

Frequently asked questions

Does this call an external API?: No. There are no fetch requests; everything runs in your browser.
Why doesn’t it show my city or ISP?: That would require a database or network lookup. This page is a reference and classifier only.

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