Reverse DNS / PTR lookup
Resolves the PTR hostnames of a public IP address plus ASN, provider and country — useful for FCrDNS checks and classifying server requests in logs.
How this tool works
Reverse DNS or PTR lookup determines the hostname(s) mapped to an IP address — the inverse of the classic A/AAAA record. The tool also surfaces the primary hostname plus ASN, provider and country as context. This lets you identify the host and provider behind a request in server logs and verify whether a mail server has clean FCrDNS (Forward Confirmed Reverse DNS) — a prerequisite for good deliverability. Private and reserved ranges have no public PTR and are rejected.
Typical use cases
- Map an IP from the access log to a hostname and provider
- Before blocking, verify whether an IP belongs to Googlebot, BingBot or another legitimate crawler
- Verify a mail servers FCrDNS — the PTR must point to a hostname whose A record resolves back to the same IP
- On attack suspicion, determine the source ASN and responsible provider
- Check IPv6 addresses for hostnames via ip6.arpa PTR
Frequently asked questions
Why does an IP have no PTR record?
The responsible provider must set the PTR explicitly. On residential lines it is often empty, on server providers usually populated. A missing PTR makes a mail IP immediately suspect to many spam filters.
What is FCrDNS and why does it matter?
Forward Confirmed Reverse DNS: the PTR of the IP points to a hostname whose A record resolves back to the same IP. Mail servers without clean FCrDNS land in spam more often — large providers enforce this.
How do I tell real Googlebot from a fake?
Real Googlebot has a PTR on *.googlebot.com or *.google.com, and the A record of that hostname must resolve back to the same IP (FCrDNS). If both directions match, it is genuine.
Does the lookup work with IPv6?
Yes. IPv6 addresses are translated into ip6.arpa PTR queries. An IP can have multiple PTR records, which the tool lists all of.
Are private IP addresses supported?
No. Reserved and private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, loopback) have no public PTR and are rejected.
Does the tool store the queried IPs?
No. The query is processed in memory and not stored for tracking purposes. The page is cookieless.
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