Reverse DNS lookup

Use this reverse DNS lookup to find a PTR hostname for an IP address. Check whether it resolves back to the same address before reviewing mail server DNS.

Free, no account. Thirty lookups per hour.

Public IPv4 and IPv6 addresses only. A hostname is looked up first, then each of its addresses. An answer is reused for five minutes.

A reverse DNS lookup reads the hostname stored in an IP address’s PTR record. This tool then looks that hostname up to see whether it points back to the same address, which is called forward-confirmed reverse DNS. Receiving mail servers check it, and Google tells site owners to use it to verify Googlebot.

How to use this tool

Enter an address or a hostname
Paste an IPv4 or IPv6 address, for example from a server log. A hostname works too: we resolve it first and check each public address it has. Private, loopback, link-local and reserved addresses are refused.
Reverse, then forward
We read the PTR record for the address, then look up each name it lists. When one of those names resolves back to the same address, the result is forward-confirmed (FCrDNS). Whoever controls an address can write any name into its PTR record, so an unconfirmed name proves nothing.
Crawler checks
A confirmed name ending in googlebot.com, google.com or googleusercontent.com belongs to Google, as its verification guide explains. Bingbot, Applebot, YandexBot and Baiduspider are recognised from their published domains the same way. OpenAI publishes IP ranges instead, so we also check the address against its lists for GPTBot, OAI-SearchBot, ChatGPT-User and OAI-AdsBot.

Questions before you start

It is a two-way check: the PTR record of an IP address names a host, and that host’s A or AAAA record lists the same address. The PTR is set by whoever controls the address and the forward record by whoever controls the domain, so a match ties the two together.

Many receiving mail servers look up the PTR record of the server that connects to them. A missing PTR, or one that does not point back, makes the sender look like a home connection or a hijacked machine, so its mail is more likely to be rejected or filtered. Gmail’s sender guidelines ask for valid forward and reverse DNS.

Take the IP address from your server log and look it up here. Googlebot is genuine when the confirmed name ends in googlebot.com, google.com or googleusercontent.com. GPTBot is genuine when the address is inside the range OpenAI publishes for it. Anyone can copy a user agent string, so it proves nothing on its own.

The owner of the IP address, usually your hosting company, cloud provider or internet provider, not your domain registrar. Look for a reverse DNS setting in the server’s control panel, or ask the provider to set it.

Addresses such as 10.0.0.1, 192.168.1.1 or 127.0.0.1 only mean something inside one network, so a public lookup has nothing to say about them. Refusing them also keeps the tool from being used to probe internal systems.

Related tools

  • MX lookup

    Use this MX lookup to inspect mail server priorities, IP addresses, provider hints and forward-confirmed reverse DNS. Review routing findings and a bounded public SpamCop check.

  • DNS checker

    Use this DNS checker to read records and TTLs for a domain. Compare public and authoritative answers, then review mail, alias and DNSSEC findings.

  • Crawler IP checker

    Use this crawler IP checker to compare up to 50 addresses with published bot ranges. Paste IPs or a log excerpt, then review the operator matches.

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