Reverse DNS

Resolve any IP address to its hostname using PTR record lookup. Free reverse DNS tool to verify rDNS configuration for email servers, security analysis, and network diagnostics.

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APIPOST /api/v1/dns/reverse
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Try also: IP Geolocation
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Key Features

100% Free

No registration required, unlimited checks

Instant Results

Real-time analysis with detailed output

REST API Access

Integrate into your workflow via API

Accurate Data

Live queries to authoritative sources

What is Reverse DNS?

Reverse DNS (rDNS) resolves an IP address back to its associated hostname by querying PTR records in the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones. This is the opposite of a standard forward DNS lookup, which translates domain names into IP addresses. Reverse DNS plays a critical role in email deliverability — most major mail providers (Gmail, Outlook, Yahoo) check that a sending server's IP has a valid PTR record matching its hostname, and reject or spam-flag messages from servers without proper rDNS configuration.

Beyond email, reverse DNS is used for security investigations to identify the hostname behind a suspicious IP address, network diagnostics to verify server configurations, log analysis to resolve IP addresses to readable hostnames, and access control lists that rely on hostname-based rules. This free online reverse DNS lookup tool supports both IPv4 and IPv6 addresses and returns PTR records instantly without requiring command-line access.

How to Use

  1. 1Enter the IPv4 or IPv6 address you want to resolve (e.g., 8.8.8.8 or 2001:4860:4860::8888)
  2. 2Click 'Run Check' to perform a PTR record lookup against the in-addr.arpa zone
  3. 3Review the hostname returned — this is the domain name associated with the IP address
  4. 4Verify that the PTR record matches the expected forward DNS configuration (forward-confirmed reverse DNS)
  5. 5For email servers, confirm the PTR hostname matches your mail server's HELO/EHLO identity

Who Uses This

System Administrators

Monitor and troubleshoot infrastructure

Developers

Debug network issues and integrate via API

SEO Specialists

Verify domain configuration and performance

Security Analysts

Audit and assess network security

Frequently Asked Questions

What is reverse DNS and how does it work?
Reverse DNS (rDNS) is a DNS query that resolves an IP address to its associated hostname using PTR (Pointer) records. While forward DNS maps domain names to IP addresses (example.com → 93.184.216.34), reverse DNS does the opposite (93.184.216.34 → example.com). For IPv4 addresses, the lookup queries the in-addr.arpa zone by reversing the IP octets. For example, looking up 8.8.8.8 queries 8.8.8.8.in-addr.arpa. IPv6 reverse lookups use the ip6.arpa zone with each nibble separated by dots.
Why is reverse DNS important for email deliverability?
Most major email providers — including Gmail, Microsoft 365, and Yahoo Mail — check the reverse DNS of incoming mail servers as part of their spam filtering. If your mail server's IP address doesn't have a valid PTR record, or if the PTR hostname doesn't match the server's HELO/EHLO identity, your emails are much more likely to be rejected or delivered to spam folders. A properly configured rDNS is one of the fundamental requirements for email authentication, alongside SPF, DKIM, and DMARC.
How do I set up reverse DNS for my IP address?
Reverse DNS (PTR records) must be configured by the organization that controls the IP address block — typically your hosting provider, VPS provider, or ISP. You cannot set PTR records in your own DNS zone. Contact your provider and request a PTR record pointing your IP address to your server's fully qualified hostname (e.g., mail.example.com). Most cloud providers like AWS, Google Cloud, and DigitalOcean offer PTR record management through their control panels.
What is forward-confirmed reverse DNS (FCrDNS)?
Forward-confirmed reverse DNS means that the PTR record for an IP resolves to a hostname, and that hostname's A record resolves back to the same IP address. For example: 93.184.216.34 → PTR → example.com → A → 93.184.216.34. This bidirectional verification is considered the gold standard for server identity validation and is checked by many email providers and security systems. If either direction fails, it's called a 'broken' reverse DNS configuration.
Can I do reverse DNS lookup for IPv6 addresses?
Yes — this tool supports both IPv4 and IPv6 reverse DNS lookups. IPv6 PTR records work the same way as IPv4 but use the ip6.arpa zone instead of in-addr.arpa. Enter the full IPv6 address (e.g., 2001:4860:4860::8888) and the tool will query the appropriate reverse zone. IPv6 reverse DNS is increasingly important as more servers and email providers adopt IPv6 connectivity.

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API Endpoint

POST /api/v1/dns/reverse
View Documentation