Resolve any IP address to its PTR hostname, with forward-confirmation (FCrDNS) and the announcing network.
Try: 8.8.8.8, 1.1.1.1 or your own IP
No PTR record found. This is common — reverse DNS is optional and many networks don't configure it (see the FAQ below).
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Reverse DNS inverts the usual name-to-address direction: given an IP, it asks DNS for the name.
For 8.8.8.8 the resolver queries the PTR record of
8.8.8.8.in-addr.arpa (IPv4 octets reversed); IPv6 uses ip6.arpa with
every hex nibble reversed. Control over those zones follows the address allocation itself:
regional registries delegate them to the ISP or hosting company holding the block, which is why
you can't set a PTR record from your domain's DNS panel.
This tool resolves the PTR server-side and then performs the step most lookup tools skip:
forward confirmation. A PTR is only meaningful if the hostname it returns
resolves back to the same IP (FCrDNS). Without that check, reverse DNS is trivially spoofable —
the block owner can point 1.2.3.4 at mail.google.com and unconfirmed
tools will happily display it.
Where you'll use this in practice: mail delivery (receivers like Gmail
effectively require valid FCrDNS on sending IPs), log analysis (a PTR like
crawl-66-249-66-1.googlebot.com — forward-confirmed — is how you verify a crawler
is really Googlebot), traceroute reading (router PTRs encode location and
interface, like ae-1.cr1.fra2.example.net), and abuse triage,
where the PTR often identifies the customer or product behind an address faster than whois.
The lookup runs against the live DNS tree with a short timeout; the ASN line comes from our local routing snapshot, so you immediately see which network is responsible for the address even when no PTR exists.
A PTR (pointer) record maps an IP address back to a hostname — the opposite direction of an A or AAAA record. PTR records live in the special in-addr.arpa (IPv4) and ip6.arpa (IPv6) DNS zones, which are delegated to whoever controls the address block, usually the ISP or hosting provider.
FCrDNS checks that the PTR hostname also resolves back to the original IP address. Since anyone controlling an address block can set its PTR to any name (even google.com), the forward confirmation is what makes reverse DNS trustworthy. Mail servers use FCrDNS heavily for spam filtering.
PTR records are optional and must be created by whoever controls the IP block. Many residential ISPs and cloud instances simply don't set them. A missing PTR is normal for consumer connections, but for a mail server it's a problem — most receivers will reject or spam-folder mail from IPs without valid reverse DNS.
Only the holder of the address block can. On cloud providers (AWS, Hetzner, OVH, DigitalOcean) you can usually set the PTR for your instance's IP in the control panel or via a support request. For a residential connection you'd have to ask your ISP, which rarely offers it on consumer plans.
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