Reverse DNS
free/v1/ip/reversePerforms a reverse DNS lookup (PTR record query) to find the hostname(s) associated with an IP address. Validates forward-confirmed reverse DNS (FCrDNS) and detects hostname patterns. Essential for email deliverability validation and infrastructure reconnaissance.
What It Does
Queries PTR records for the IP address by looking up the in-addr.arpa (IPv4) or ip6.arpa (IPv6) domain via Cloudflare DoH. Returns all associated hostnames, performs forward-confirmed reverse DNS (FCrDNS) validation by resolving each PTR hostname back to verify it matches the original IP, and classifies detected hostname patterns (e.g., mail servers, CDNs, residential ISP naming conventions).
Why It's Useful
Reverse DNS is critical for email deliverability since Google and Yahoo require Forward-Confirmed Reverse DNS (FCrDNS) as of February 2024. It enables security analysts to resolve IPs in logs to meaningful hostnames, and penetration testers to discover infrastructure during reconnaissance. Missing or misconfigured PTR records are a leading cause of email delivery failures.
Use Cases
Email Deliverability Audit
Verify that all mail server IPs have proper PTR records matching the HELO/EHLO hostname, and that FCrDNS passes. Required by Google and Yahoo since February 2024.
Prevent email delivery failures caused by missing or mismatched reverse DNS records.
Security Log Enrichment
Enrich firewall, IDS, and server access logs with hostnames to identify patterns like scanning from cloud providers or known botnet infrastructure.
Transform raw IP logs into actionable intelligence with meaningful hostname context.
Infrastructure Reconnaissance
Map IP ranges to hostnames during authorized penetration testing to discover additional subdomains, services, and shared hosting environments.
Expand attack surface understanding by uncovering hidden services and infrastructure relationships.
Parameters
| Name | Type | Required | Description |
|---|---|---|---|
ip | string | Required | The IPv4 or IPv6 address to perform reverse DNS lookup onExample: 8.8.8.8 |
Response Fields
| Field | Type | Description |
|---|---|---|
ip | string | The queried IP address |
ip_version | number | IP version (4 or 6) |
hostnames | array | All PTR record hostnames found (trailing dots removed) |
has_ptr | boolean | Whether any PTR record was found |
fcrdns | array | Forward-confirmed reverse DNS results: hostname, forward_confirmed (boolean), forward_addresses |
hostname_classification | string | Detected hostname pattern: mail_server, nameserver, cdn, web_server, gateway, residential, static_ip, or cloud_compute |
Code Examples
curl "https://api.edgedns.dev/v1/ip/reverse" \
-H "Authorization: Bearer YOUR_API_KEY" \
-d "ip=8.8.8.8"const response = await fetch(
'https://api.edgedns.dev/v1/ip/reverse?ip=8.8.8.8',
{
headers: {
'Authorization': 'Bearer YOUR_API_KEY'
}
}
);
const data = await response.json();
console.log(data);import requests
response = requests.get(
'https://api.edgedns.dev/v1/ip/reverse',
headers={'Authorization': 'Bearer YOUR_API_KEY'},
params={
'ip': '8.8.8.8'
}
)
data = response.json()
print(data)Read the full Reverse DNS guide
Why it matters, real-world use cases, parameters, response fields, and how to call it from Claude, ChatGPT, or Gemini via MCP.
Read the guide →Related Endpoints
External References
Learn more about the standards and protocols behind this endpoint.