Reverse DNS (PTR) Lookup
Find the hostname an IP address points back to — its PTR record — for any IPv4 or IPv6 address, with a forward-confirmed (FCrDNS) check. Fast, free and nothing is stored.
About reverse DNS
Every IP address can publish a PTR record that names the host it belongs to — the
reverse of the usual A/AAAA lookup. Reverse DNS is set by whoever controls the IP block (the hosting
provider or ISP), stored in the in-addr.arpa zone for IPv4 and ip6.arpa for
IPv6. It matters most for email: a sending mail server with no PTR, or a PTR that
does not forward-confirm back to its IP, is far more likely to have its mail rejected or marked as
spam. This tool resolves the PTR over public DNS and then checks whether the hostname resolves back
to the same IP (forward-confirmed reverse DNS, or FCrDNS).
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Frequently asked questions
What is a reverse DNS (PTR) lookup?
Forward DNS turns a hostname into an IP address; a reverse DNS lookup does the opposite — it asks which hostname an IP address points back to, using its PTR record in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zone.
What is FCrDNS (forward-confirmed reverse DNS)?
It is a two-way check: the IP's PTR record resolves to a hostname, and that hostname's A/AAAA record resolves back to the same IP. Mail servers use FCrDNS as a basic trust signal — mail from an IP without matching forward and reverse DNS is far more likely to be marked as spam.
Why does an IP have no PTR record?
PTR records are controlled by whoever owns the IP block (usually the hosting provider or ISP), not by the domain owner. Many residential and some server IPs simply have no PTR set, which is normal but can hurt deliverability for a mail server.
How is this different from a reverse IP lookup?
A reverse IP lookup finds other websites hosted on the same IP. A reverse DNS (PTR) lookup finds the single hostname the IP officially points to. For the full forward records of a domain, use the DNS Lookup.