Question 1

Does this tool perform live reverse DNS lookups?

Accepted Answer

No. Reverse DNS lookups require the network — and this tool is 100% client-side, so it generates the exact `dig -x`, `nslookup -type=PTR`, `kdig` (DoH), and `host` commands for you to copy and run in your terminal against your chosen resolver (Google 8.8.8.8, Cloudflare 1.1.1.1, Quad9 9.9.9.9, OpenDNS, or a custom IP/host). The reverse-zone name (in-addr.arpa / ip6.arpa) is constructed locally and works offline. PTR records are maintained by the IP owner/ISP, so many addresses legitimately have no PTR.

Question 2

How is the in-addr.arpa / ip6.arpa name built?

Accepted Answer

For IPv4, the four octets are reversed and appended to `.in-addr.arpa` — e.g. `192.0.2.1` → `1.2.0.192.in-addr.arpa`. For IPv6, the address is first fully expanded to 32 hex nibbles, each nibble is reversed, and the result is appended to `.ip6.arpa` — e.g. `2001:db8::1` → `1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa`. The tool always shows the generated zone name alongside every command so you can verify the lookup target.

Question 3

What is FCrDNS and how does this tool help with it?

Accepted Answer

FCrDNS (Forward-Confirmed Reverse DNS) is a two-step check mail servers run: (1) query the PTR for the IP → hostname; (2) query A/AAAA for that hostname → IP set; (3) verify the original IP is in that set. It is the PTR check that actually matters for email deliverability. The tool generates the full chain (PTR query + A/AAAA query for the returned hostname) so you can run both halves in your terminal and compare answers manually. When the chain fails, you get a deliverability explanation to share with the IP owner.

Question 4

How are CIDR ranges handled?

Accepted Answer

Enter a CIDR like `192.0.2.0/30` and the tool enumerates every host IP in the range (capped at 256 to keep command output sane — `/24` for IPv4 and `/120` for IPv6 are the practical limits), then generates a PTR query per address. Larger CIDRs are rejected with a clear error message and a suggestion to narrow the range. Each generated address has its own reverse-zone name, dig/nslookup/kdig/host command, and copy button.

Question 5

What extra features does this tool have versus other reverse DNS sites?

Accepted Answer

(1) Correct IPv4 in-addr.arpa construction. (2) Correct IPv6 ip6.arpa (nibble-reversed) construction with full expansion. (3) CIDR range enumeration with a 256-address cap. (4) FCrDNS chain builder (PTR + A/AAAA). (5) Private/loopback/link-local/reserved IP detection — flagged so you don't waste queries. (6) dig / nslookup / kdig (DoH) / host command variants. (7) 5 resolver presets (Google, Cloudflare, Quad9, OpenDNS, custom). (8) PTR zone-record parser (name TTL IN PTR target). (9) Batch .sh script generator for ranges. (10) Hostname → IP → PTR convenience chain. (11) Copy-to-clipboard per command. (12) localStorage history (max 20). (13) Shareable URL. 100% client-side — never sends queries itself.

Reverse DNS (PTR) Lookup Generator

Settings

Generated Commands (4)

Hostname → IP → PTR chain (using dig)

How to use

Settings

Generated Commands (4)

Hostname → IP → PTR chain (using dig)