Find the hostname (PTR) for any IP — with FCrDNS verification
A reverse DNS lookup is the opposite of a normal DNS query: instead of resolving a hostname to an IP, it asks "what hostname is associated with this IP?". This works through PTR (pointer) records published in special reverse DNS zones — in-addr.arpa for IPv4 and ip6.arpa for IPv6. The IP is reversed (so 8.8.8.8 becomes 8.8.8.8.in-addr.arpa) and the resulting name is queried. Only the network operator that owns the IP block can publish PTR records, which makes them a useful identity signal.
A PTR record alone is easy to spoof — anyone who runs DNS for an IP block can claim any hostname they like. Forward-confirmed reverse DNS adds verification: after looking up the PTR, the tool resolves that hostname back to A or AAAA records and checks whether the original IP appears in the result. Only when both directions match does the IP truly "own" the name. Mail servers especially rely on FCrDNS — many will downgrade or reject mail from senders whose reverse and forward records do not match.
Reverse DNS is essential for diagnosing email deliverability problems, identifying which company operates a given IP, debugging spam reports, and matching log entries with friendly hostnames. To use this tool, enter any public IPv4 or IPv6 address. It will fetch all PTR records and forward-confirm each one, telling you which hostnames are legitimately tied to the IP and which are not.
Reverse DNS is published by whoever controls the IP block, not by you. If you run a server on a residential ISP or a small VPS provider, the upstream may not have set a PTR for your IP — or it may point to a generic name like "static-1-2-3-4.example-isp.net". Most reputable hosts (AWS, GCP, Linode, DigitalOcean, OVH) let you set a custom PTR via their control panel. Setting a meaningful PTR is especially important if you send email from the IP.
Spammers historically abused IPs without proper reverse DNS, so anti-spam filters now treat missing or generic PTRs as a negative signal. Many large providers (Gmail, Outlook, Yahoo) require a working PTR that forward-confirms back to the same IP before they will accept mail. Even when accepted, mail from senders without FCrDNS is more likely to be filtered. Setting a hostname that points back via PTR — and that resolves forward to the same IP — is one of the cheapest deliverability fixes available.
Technically yes. The DNS specification allows multiple PTR records for one IP, and the tool will display all of them. In practice it is unusual and slightly problematic — many resolvers cache only the first response, and some applications assume a single record. The convention is one PTR per IP. If you need multiple hostnames to share an IP, use forward DNS (multiple A/AAAA records) and set the PTR to one canonical hostname.
Reverse DNS is delegated from the regional internet registries (ARIN, RIPE, APNIC, etc.) down through ISPs to end customers. For a server in a cloud provider, look for a "reverse DNS" or "PTR" setting in your instance configuration. For a colocated server with assigned static IPs, file a request with your hosting provider. For your home or office IP, your ISP probably will not change it — most ISPs publish a generic reverse name and decline customer requests.
They are two parallel reverse DNS hierarchies, one per IP version. The IPv4 zone is in-addr.arpa: an IP like 8.8.8.8 is reversed to 8.8.8.8.in-addr.arpa. The IPv6 zone is ip6.arpa: each hex digit is reversed and dotted, so 2001:db8::1 becomes 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. The tool handles both formats automatically — you just paste the address.
