Reverse IP¶

The Reverse IP API provides a list of domain names that share the same Internet host (i.e. the same IP address). You can request an IP address directly, or you can provide a domain name; if you provide a domain name, the API will respond with the list of other domains that share the same IP.

Understanding Reverse IP Results¶

The Reverse IP tool tracks a single IP address per domain in the legacy system. When a domain resolves to multiple IP addresses, only one IP (typically the "lowest" IP address) is tracked. This means:

Results represent a subset of all domains on a given IP address, not an exhaustive list
For shared hosting environments with many domains, you may see only a portion of the total domains
The domain_count response value indicates the total number of domains known for that IP, which may exceed the number of domains actually returned in the results

Use Cases and Limitations¶

Appropriate Use Cases¶

The Reverse IP API is best suited for:

Investigative research on specific domains and their hosting relationships
Finding related domains on smaller shared hosting environments
Initial reconnaissance and infrastructure mapping
Understanding hosting patterns for domains of interest

Limitations for High-Volume IPs¶

The Reverse IP API is not designed for:

Exhaustive enumeration of large content delivery networks (CDNs) or cloud hosting providers such as Cloudflare, Amazon Web Services, or Google Cloud
Complete audits or inventories of high-volume IP addresses that may host millions of domains
Bulk data extraction at scale

For IP addresses hosting very large numbers of domains (such as those used by major CDN providers), the Reverse IP API will return only a subset of domains. Full enumeration of all domains on high-volume IPs is not possible with this tool.

Alternative Tools¶

Depending on your use case, consider these alternative DomainTools products:

Iris Investigate API¶

The Iris dataset tracks all actively resolved IP addresses for apex domains and is updated daily. Iris is designed for investigative pivoting and finding related infrastructure but is not intended for mass enumeration of millions of domains.

Learn more about Iris Investigate

DNSDB¶

DNSDB provides broader historical DNS data coverage and can return more comprehensive results for reverse IP lookups. However, DNSDB has its own limitations:

Result limits (approximately 4 million records per query)
API access is more scalable than the web interface but still has constraints
Requires separate DNSDB API access

Learn more about DNSDB

Best Practices¶

Request IP Addresses Directly¶

When possible, query using explicit IP addresses rather than domain names. This provides more predictable results and avoids uncertainty when domains resolve to multiple IPs:

Preferred: https://api.domaintools.com/v1/64.246.165.240/host-domains/
Less predictable: https://api.domaintools.com/v1/domaintools.com/reverse-ip/

Interpret Results Appropriately¶

When domain_count exceeds the number of returned domains, recognize that you're seeing a subset
Focus on the domains that are returned rather than trying to obtain a complete list
For investigative purposes, prioritize analyzing recent and relevant domains

Combine Tools for Comprehensive Investigation¶

For thorough infrastructure analysis:

Use Reverse IP for initial quick lookups
Pivot to Iris Investigate for current, comprehensive IP resolution data
Query DNSDB for historical context and broader coverage when needed

Understanding Result Limits¶

The limit parameter controls how many domains are returned per IP address. However:

System-level limits may also apply based on your service level
Setting a higher limit will not return domains beyond what is tracked in the database
For high-volume IPs, increasing the limit will still return only a subset of total domains

API Usage¶

https://api.domaintools.com/v1/domaintools.com/reverse-ip/
https://api.domaintools.com/v1/64.246.165.240/host-domains/

When a domain name resolves to multiple IP addresses, the ip_addresses response node will have several containers, each with an ip_address, domain_count and domain_names node. Otherwise, those nodes will be included directly as children of the ip_addresses node.

Reverse IP Parameters¶

Optional Parameters	Value
`limit`	Limits the size of the domain list that can appear in a response. The limit is applied per-IP address, not for the entire request.

Using the Limit Parameter¶

The optional limit parameter controls the size of the result list:

Domains that resolve to multiple IP addresses may return more than the limit you set if your request is for a domain name instead of an IP address
We recommend requesting explicit IP addresses whenever possible to avoid this uncertainty
The limit is applied per IP address in the response, not to the total number of results

Understanding Limited Results¶

If the domain_count response value is greater than the count of elements in the domain_names list, your query has been limited. This means:

You're seeing only the first set of domains on that IP address, listed alphabetically
The limit may come from your service level, the limit parameter you set in your request, or system-level constraints
For high-volume IPs: Increasing the limit will not provide complete results because the underlying data only tracks one IP per domain

This is expected behavior, not an error. The tool is designed for investigative research on specific hosting relationships, not exhaustive enumeration.

Sample Response¶

{
  response: {
    ip_addresses: [
      {
        domain_count: 1,
        domain_names: ['DOMAINTOOLS.NET'],
        ip_address: '199.30.228.77'
      },
      {
        domain_count: 3,
        domain_names: ['DOMAINTOOLS.COM',
                       'SANTASFAVORITEWHOIS.COM',
                       'WHOISSUGGEST.COM'],
        ip_address: '8.247.14.160'
      },
      ...
     ]
  }
}

Sample Queries¶

HTML: https://api.domaintools.com/v1/domaintools.com/reverse-ip/?format=html
JSON: https://api.domaintools.com/v1/domaintools.com/reverse-ip/
XML: https://api.domaintools.com/v1/domaintools.com/reverse-ip/?format=xml