Internet Corporation for Assigned Names and Numbers (ICANN) maintains and distributes IP addresses. This organization distributes IP addresses to various businesses and organizations, which in turn attribute them to their customers. However, they still retain their ownership.

IP addresses are available publicly and do not lead to personally identifiable information, so it is legal to check someone's IP address by using an IP lookup tool.

Nothing. While their names may differ, they are all exactly the same tool – and are designed to find your IP address and your IP geolocation, as well as showing you the ISP associated with your IP address.

In Windows, go to All Programs -> Accessories. Then right-click on Command Prompt. Choose Run As Administrator and type in nslookup %ipaddress% putting an IP address instead of %ipaddress%

The reverse IP finder allows you to find all the domains associated with a specific IP address. For example, you can check what other websites are stored on the server you use to avoid bad neighbors. The reverse IP lookup is also useful to find out how many sites are stored on servers to prevent overcrowded web hosting.

The IP lookup tool is completely free, and you can use it at your own discretion. IP addresses are publicly available, so any internet user has the right to check them.

As of 2018-07-25 it's no longer possible to force protocol using the v4 and v6 subdomains. IPv4 or IPv6 still can be forced by passing the appropiate flag to your client, e.g curl -4 or curl -6.

Setting the Accept: application/json header works as expected.

Yes, as long as the rate limit is respected. The rate limit is in place to ensure a fair service for all. Please limit automated requests to 5 request per minute. No guarantee is made for requests that exceed this limit. They may be rate-limited, with a 429 status code, or dropped entirely or get the lite database