Reverse DNS (PTR) Lookup
Give it an IP address and get back the hostname registered for it, the inverse of a normal DNS query. Used for identifying servers in logs, verifying mail server configuration, and checking what an unknown IP claims to be.
How to use
- Enter an IPv4 or IPv6 address.
- Click Run to query its PTR record.
- Compare the returned hostname with what you expected the IP to be.
Forward DNS answers 'what IP does this name point to?'. Reverse DNS answers 'what name is registered for this IP?'. The mechanism is a PTR record in a special zone (in-addr.arpa for IPv4), controlled not by domain owners but by whoever owns the IP block, typically your hosting provider or ISP. That distinction explains most reverse-DNS confusion: you can point your A record anywhere in your registrar panel, but the PTR for your server's IP is set in your cloud provider's console.
The highest-stakes use is email. Receiving mail servers routinely check that a connecting server's IP has a PTR record, and that it round-trips, the PTR's hostname should resolve forward to the same IP (forward-confirmed reverse DNS). Servers without matching PTR records get their mail rejected or spam-foldered by Gmail and Outlook. If you run your own mail server, setting the PTR is not optional.
Beyond mail, reverse DNS is a log-analysis workhorse: a suspicious IP in your access logs resolving to crawl-66-249-66-1.googlebot.com (verify with a forward lookup, PTR alone is spoofable by the IP owner) is very different from one resolving to a residential ISP pool or to nothing at all. Many corporate and cloud IPs have no PTR, absence is common and not by itself suspicious.
Examples
Input: 8.8.8.8
Output: PTR: dns.googleInput: 1.1.1.1
Output: PTR: one.one.one.oneFrequently asked questions
How do I set the PTR record for my server?
Through whoever allocates the IP, your cloud/hosting provider's console (AWS, DigitalOcean, and others expose it directly), not your domain registrar. Set it to your mail server's hostname and make sure that hostname's A record points back at the same IP.
Why does my outgoing email need reverse DNS?
Major receivers treat a missing or generic PTR as a spam signal, most spam comes from compromised machines without proper reverse DNS. Forward-confirmed reverse DNS (PTR and A record agreeing) is baseline deliverability hygiene alongside SPF, DKIM, and DMARC.
Can a PTR record lie?
The IP block's owner can set any PTR they want, so yes, a PTR claiming to be googlebot proves nothing alone. Verify by resolving the claimed hostname forward: for genuine Googlebot, the hostname resolves back to the same IP.
Why does an IP have no PTR record?
The block owner never configured one, extremely common for cloud instances, CDN ranges, and residential connections. Absence is unremarkable. A present-and-round-tripping PTR is the meaningful signal.
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