Reverse Nameserver Lookup
Find every domain delegated to a specific nameserver. Enter a nameserver hostname to discover all domains using it across 1,100+ TLDs.
“A nameserver serves thousands of domains. Reverse NS lookup shows you every one of them.”
Written by Ishan Karunaratne · Last reviewed:
What Is a Reverse Nameserver Lookup?
A standard DNS lookup tells you which nameservers a domain uses. A reverse nameserver lookup works the other way: given a nameserver hostname, it returns every domain delegated to that nameserver. This is possible because DNS delegation is recorded in TLD zone files as NS records, and DNS Checker indexes these records daily across over 1,100 top-level domains.
For example, looking up ns1.google.com returns every domain in the indexed zone files that has an NS record pointing to that nameserver. The results reveal the full scope of domains relying on a particular piece of DNS infrastructure.
Use Cases
Competitor Research
Find all domains managed by the same DNS provider to understand a competitor's infrastructure footprint.
Infrastructure Mapping
Map the full scope of domains relying on specific nameservers for capacity planning and risk assessment.
Security Audits
Identify all domains sharing nameservers with a suspicious or compromised domain during incident response.
Migration Planning
Audit every domain delegated to nameservers being decommissioned to ensure nothing is missed during a migration.
Market Research
Estimate the customer base of DNS providers by counting domains across their nameserver pool.
Brand Protection
Monitor nameservers associated with known phishing or typosquatting infrastructure for new domain registrations.
How It Works
DNS Checker processes zone file data from over 1,100 TLDs daily, extracting NS record delegations for every domain. This data is indexed by nameserver hostname, allowing instant reverse lookups across the entire dataset of 250+ million domains.
When a reverse NS lookup is performed, the tool queries this index for all domains whose NS records include the specified nameserver. Results are sorted by domain name and include the TLD, the date the delegation was first observed, and when it was last confirmed in the zone file.
Because zone files are refreshed daily, results reflect current DNS delegations. Domains that have changed nameservers or been deleted will show an older "Last Seen" date as the zone data updates.
Related Tools
- •DNS Inspector — Look up all DNS records for any domain, including NS, A, AAAA, MX, and TXT
- •Propagation Checker — Check DNS propagation status across global resolvers
- •WHOIS Lookup — Find registration details, registrar, and expiry date for any domain
- •Domain Availability — Check if a domain name is available for registration
Need this in code?
Every check this tool runs is also available via the reverse NS API with examples in cURL, JavaScript, Python, PHP, Ruby, and Java.
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