A reverse DNS (rDNS) lookup maps an IP address back to the hostname its operator has published. Unlike a normal forward lookup (hostname → IP), rDNS relies on a PTR record on the in-addr.arpa (IPv4) or ip6.arpa (IPv6) tree, which the network owning the IP block is responsible for publishing.
This tool queries the authoritative resolvers directly and streams the answer back.
Why it matters
- Email deliverability — mail servers without a matching PTR are frequently marked as spam.
- Log analysis — translating raw IPs into readable hostnames makes traffic logs human-friendly.
- Security research — PTR records often leak who owns an IP (e.g. ec2-54-…compute.amazonaws.com).
FAQ
Why is there no PTR for my IP? rDNS zones are delegated by the network owner. Home users rarely have PTR control; ask your ISP or hosting provider.
Does rDNS have to match forward DNS? No, but matching (FCrDNS — Forward-Confirmed Reverse DNS) is required by many mail receivers and improves deliverability.
Can I have more than one PTR? Technically yes, but most resolvers return only the first. Some mail systems will reject IPs with multiple PTRs.