Reverse DNS (PTR) Lookup
Resolve the PTR record for any IPv4 or IPv6 address — the hostname the IP's owner configured in reverse DNS. Reveals hosting providers, mail-server identities and corporate naming; a missing PTR on a mail source is also a deliverability red flag.
🔌 Server-side tool
This tool runs on the server (it fetches third-party URLs directly and cannot run in your browser). Use the paid JSON API below — the worked examples show real server-side results and refresh automatically.
Worked examples
Google DNS
GET /api/v1/security/reverse-dns?ip=8.8.8.8
Result: 8.8.8.8 → dns.google (forward-confirmed ✓)
Cloudflare
GET /api/v1/security/reverse-dns?ip=1.1.1.1
Result: 1.1.1.1 → one.one.one.one (forward-confirmed ✓)
An IPv6 address
GET /api/v1/security/reverse-dns?ip=2606%3A4700%3A4700%3A%3A1111
Result: 2606:4700:4700::1111 → one.one.one.one
Machine API (x402)
$0.02 / callThis tool is also a JSON API for AI agents. Requests without payment receive 402 Payment Required plus instructions; agents pay USDC on Base via the x402 protocol — no accounts, no API keys.
GET /api/v1/security/reverse-dns?ip=8.8.8.8 HTTP/1.1
Host: agentstoolshub.com
→ 402 (payment required, instructions in headers)
→ 200 (after X-PAYMENT header; JSON body below)
{
"tool": "security/reverse-dns",
"input": {"ip":"8.8.8.8"},
"result": { "value": 1, "answer": "8.8.8.8 → dns.google (forward-confirmed ✓)" }
}Agent docs: /llms.txt · OpenAPI spec · integration guide
About this tool
PTR lookup for IPv4 and IPv6 with forward-confirmation (FCrDNS): the hostname an IP advertises, checked by resolving it back. Beyond curiosity, it's a deliverability gate — mail servers without matching PTR records face immediate suspicion from receivers.
Frequently asked questions
What is FCrDNS and why check it?
Forward-confirmed reverse DNS: the PTR hostname resolves back to the original IP. Most receivers only trust a matching pair — a PTR without forward confirmation is worth about as much as none.
Who controls PTR records?
The network that owns the IP block (the hosting provider), not the domain owner. Setting one usually means asking your provider's panel or support.