Reverse DNS

Reverse DNS performs the opposite of a normal lookup: instead of turning a domain name into an IP address, it takes an IP address and finds the hostname associated with it. This works through PTR (pointer) records published in the special in-addr.arpa zone for IPv4 and ip6.arpa for IPv6. When you enter an address, the tool constructs the reversed query and reports the hostname the address's owner has chosen to advertise, if any.

The reverse lookup follows the same delegation model as forward DNS but in a reversed address hierarchy. The owner of an IP block (typically an ISP, hosting provider, or organization that controls the address range) is responsible for publishing PTR records. Because that authority is separate from the domain owner, a server can resolve forward to an IP that does not resolve backward to the same name, which is exactly the mismatch this tool helps you detect.

The biggest practical use case is email deliverability: most mail servers reject or flag messages from IPs whose PTR record does not match the sending hostname, a check known as forward-confirmed reverse DNS (FCrDNS). Network engineers also use reverse DNS to identify the operator of an address seen in logs, to verify that a leased IP has been correctly delegated, and to make traceroute and access-log output human-readable.

A useful tip is to always confirm that forward and reverse records agree: the hostname returned by the PTR record should itself resolve forward to the original IP. If you control a mail server and the PTR is missing or generic, ask your hosting provider to set it, since you usually cannot edit reverse zones yourself. Pair this with a standard DNS Lookup to verify the forward direction and confirm full alignment.