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Reverse DNS (PTR)

API

Resolve the hostname (PTR record) for an IP address.

What is Reverse DNS (PTR) Lookup?

Reverse DNS takes an IP address and finds the hostname (PTR record) associated with it. Where normal DNS resolves 'name → address', a reverse lookup does the opposite: 'address → name'. Both IPv4 and IPv6 addresses are supported.

This lookup also runs on the server. Browser JavaScript can't issue a PTR query for an arbitrary IP, so the address you enter is sent to the server, which queries the reverse zone (in-addr.arpa / ip6.arpa) and returns the result.

PTR records matter most for mail. Many receiving mail servers check that a sending IP's reverse DNS matches its forward DNS (forward-confirmed reverse DNS, or FCrDNS) as an anti-spam signal. Beyond mail, reverse lookups help you identify which host or organization an IP in your logs belongs to, or verify that your server's PTR is set correctly.

How to use

  1. Enter the IP address to look up (e.g. 8.8.8.8). IPv6 addresses can be entered as-is.
  2. Click 'PTR Lookup' and the server queries the reverse zone.
  3. Review the returned hostnames. If an IP has multiple PTR records they are all listed, and each has a copy button.

Frequently asked questions

It says there's no PTR record. Is that normal?
Yes — many IPs, especially residential and cloud-instance addresses, simply have no PTR set, so an empty result is expected. Only the owner of an IP block (the ISP or cloud provider) can set a PTR, so to assign one to your server's IP you must go through that provider's console or support.
Do forward and reverse DNS have to match?
Not strictly, but for a sending mail server it's effectively required. Receiving servers do FCrDNS: they take the hostname the sending IP's PTR points to, forward-resolve it, and check it comes back to the original IP. A mismatch can get your mail flagged as spam or rejected.
Where do I configure a PTR record?
Unlike forward records, PTRs are set by whoever manages the IP block. On clouds like AWS, GCP, and Azure you set it in the instance or Elastic IP settings; for a dedicated server you request it from your hosting provider.