Fully Qualified Domain API

GET

Resolve any IP address to its fully qualified domain name.

Fully Qualified Domain resolves an IP address to its fully qualified domain name using reverse DNS PTR records. It returns the host FQDN, base domain, TLD, subdomain, and domain level count.

Try it — live request, no key required

Request

GETapi.apiverve.com/v1/fullyqualifieddomain?ip=199.30.24.0

Query parameters

ipstring

Verification

Format

No key required to try it. Get a key to use it in your app.

Example

{
  "status": "ok",
  "error": null,
  "data": {
    "ip": "199.30.24.0",
    "baseDomain": "msn.com",
    "fqdn": "msnbot-199-30-24-0.search.msn.com",
    "tld": "com",
    "subdomain": "msnbot-199-30-24-0.search",
    "domainLevels": 5,
    "detected": true
  }
}

About the Fully Qualified Domain API

Fully Qualified Domain Name works by analyzing the IP address provided and getting the fully qualified domain name (FQDN). It uses DNS lookup to get the FQDN of the IP and returns the FQDN.

What people use it for

SIEM Log Enrichment: Security analysts resolve raw source IP addresses in firewall logs to identify hostnames, base domains, and top-level domains during triage.
Web Crawler Verification: To identify verified search engines, web servers check reverse DNS hostnames on incoming crawler IPs before granting rate limit exemptions.
Mail Server PTR Checks: Mail transfer agents verify incoming connection IP addresses against PTR domain levels and base domains to reject unconfigured relay servers.
Cloud Tenant Identification: Network engineers inspect resolved hostnames and subdomain structures from external server IPs to catalog multi-tenant infrastructure dependencies.

Ways to call it

One endpoint, many ways in — REST with JSON, XML, YAML and CSV, plus GraphQL and an MCP interface for AI agents.

JSON: Default REST response
XML: Markup format
YAML: Human-readable
CSV: Tabular export
GraphQL: Query language
MCP: For AI agents

View all integrations →

Other ways to use Fully Qualified Domain

Same data, same APIVerve account, same credit balance — one key works on all of them.

Give it to an AI agentConnect over MCP and your agent calls it as a native tool — Claude, Cursor, ChatGPT.on VerveKit Google Sheets or ExcelA =VERVE() formula fills a column — no script, no export, recalculates in place.on VerveSheets Ground an agent on itA cited, machine-checkable fact your model can't produce on its own.on VerveContext

Questions.

Common questions about the Fully Qualified Domain API.

Read the docs →

Is it cheap enough to look up the domain for every incoming request?

Yes. Each lookup costs 2 credits, which works out to about $0.30 per 1,000 calls on the Starter plan. Starter includes 200,000 credits per month, covering up to 100,000 lookups. You can also evaluate the service using the 100 free lookups provided each month.

What parts of the domain name does the response break down?

The response parses the resolved hostname into distinct domain components. It provides the top-level domain like com or org, isolates any subdomain portion, and counts the total domain levels present in the name.

How does the service find the domain name for an IP address?

It performs live DNS lookups against the provided IP address to retrieve its reverse DNS entry. Because it queries DNS infrastructure directly, the returned fully qualified domain reflects active network configuration.

What happens if a resolved domain does not have a subdomain?

The subdomain field will simply be empty when the hostname resolves directly at the root domain level. You will still receive the top-level domain and the domain level count in the response.

Can I use the resolved domain data inside my commercial software?

Yes, as long as you are subscribed to a paid plan. You can store and use the domain data within your internal tools, dashboards, and security systems. You may not resell or redistribute the raw domain data directly.

Request parameters — GET /v1/fullyqualifieddomain

Sent in the query string. Premium parameters are accepted on every plan but only take effect on plans that include them. Anything not listed here is dropped rather than passed through.

Required

Parameter	Type	Example	Description
`ip`Required	string	`199.30.24.0`	The IP address to get the fully qualified domain name of ip

Example request

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curl "https://api.apiverve.com/v1/fullyqualifieddomain?ip=199.30.24.0" \
  -H "x-api-key: YOUR_API_KEY"

Authentication

Send your key in the x-api-key header. That is the only auth step — no token exchange, and no per-endpoint scope to configure.

Header	When	Value
`x-api-key`Required	Every request	Your API key. Header names are case-insensitive, so `X-API-Key` is the same header.
`Authorization`Alternate	Instead of the above	`Bearer <key>` — for clients that only expose bearer auth. Resolves to the same account and the same billing.

401 is the only auth verdict

A 401 means the key is missing, invalid or expired. A 403 means the key is valid but not permitted here — blocked by a key restriction or an IP allow-list. Running out of credits is a 429.

Response — GET /v1/fullyqualifieddomain

Every APIVerve endpoint returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape.

Sample response

{
  "status": "ok",
  "error": null,
  "data": {
    "ip": "199.30.24.0",
    "baseDomain": "msn.com",
    "fqdn": "msnbot-199-30-24-0.search.msn.com",
    "tld": "com",
    "subdomain": "msnbot-199-30-24-0.search",
    "domainLevels": 5,
    "detected": true
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Field	Type	Example	Description
`ip`	string	`"199.30.24.0"`	The IP address that was looked up
`baseDomain`	string	`"msn.com"`	The last two labels of the FQDN
`fqdn`	string	`"msnbot-199-30-24-0.search.msn.com"`	The fully qualified domain name from the reverse DNS (PTR) record
`tld`	string	`"com"`	The top-level domain (e.g., com, net, org)
`subdomain`	string	`"msnbot-199-30-24-0.search"`	The subdomain portion of the FQDN, if any
`domainLevels`	number	`5`	Number of domain levels in the FQDN
`detected`	boolean	`true`	Whether a domain name was found for the IP address

Response headers

Every response carries your balance, so your own code always knows where it stands without polling anything. All four are exposed to browsers through CORS.

Header	What it carries
`x-api-remaining-credits`	Credits left in the current cycle
`x-api-credits-used`	Credits spent in the current cycle
`x-api-max-credits`	The allowance for the cycle
`x-api-version`	Version of the endpoint that answered

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change.

Status	Meaning	What to do
`400`	Input was rejected	Read `error`; it names the parameter that has to change.
`401`	Key missing or invalid	Check the header name and the key value.
`403`	Key valid, but not permitted here	A key restriction or an IP allow-list — never a bad key.
`429`	Rate limited, or out of credits	Read `error` to tell them apart, then back off or top up.

What a call costs — 2 credits per call

Credits are shared across every APIVerve API — one balance, one key, one bill. Failed requests never count against it, so a rejected input costs nothing.

Plan	Per month	Credits	Fully Qualified Domain calls	Per 1,000 calls
Free	Free	200	100	Free
Starter	$29.99	200,000	100,000	$0.30
Pro	$99.99	1,000,000	500,000	$0.20
Mega	$299.99	4,000,000	2,000,000	$0.15

Calls are what the credits buy at this API's rate — spend them here, on any of the other APIs, or across both. Nothing is reserved per endpoint.

Compare all pricing tiers →

Call it from cURL — GET /v1/fullyqualifieddomain

No SDK to install — this is a plain HTTPS call to /v1/fullyqualifieddomain with your key in the x-api-key header. Swap in a real key and it runs as-is.

cURL

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curl "https://api.apiverve.com/v1/fullyqualifieddomain" \
  -H "x-api-key: YOUR_API_KEY"

Resources

GitHubapiverve/fullyqualifieddomain-apiSource, issues and the examples this page is built from.ReferenceFully Qualified Domain API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/fullyqualifieddomainnpm apiverve-fullyqualifieddomainPyPI APIVerve.API.FullyQualifiedDomainNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Node.js — GET /v1/fullyqualifieddomain

Install the Node.js SDK, then call the Fully Qualified Domain API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — npm

npm install @apiverve/fullyqualifieddomain

Node.js

const res = await fetch("https://api.apiverve.com/v1/fullyqualifieddomain", {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const { data } = await res.json();
console.log(data);

Resources

npm@apiverve/fullyqualifieddomainThe published Node.js client, versioned and signed.GitHubapiverve/fullyqualifieddomain-apiSource, issues and the examples this page is built from.ReferenceFully Qualified Domain API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

apiverve-fullyqualifieddomainPyPI APIVerve.API.FullyQualifiedDomainNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Python — GET /v1/fullyqualifieddomain

Install the Python SDK, then call the Fully Qualified Domain API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — PyPI

pip install apiverve-fullyqualifieddomain

Python

import requests

res = requests.get(
    "https://api.apiverve.com/v1/fullyqualifieddomain",
    headers={"x-api-key": "YOUR_API_KEY"},
)
print(res.json()["data"])

Resources

PyPIapiverve-fullyqualifieddomainThe published Python client, versioned and signed.GitHubapiverve/fullyqualifieddomain-apiSource, issues and the examples this page is built from.ReferenceFully Qualified Domain API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/fullyqualifieddomainnpm APIVerve.API.FullyQualifiedDomainNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from C# / .NET — GET /v1/fullyqualifieddomain

Install the C# / .NET SDK, then call the Fully Qualified Domain API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — NuGet

dotnet add package APIVerve.API.FullyQualifiedDomain

C# / .NET

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("x-api-key", "YOUR_API_KEY");

var json = await client.GetStringAsync("https://api.apiverve.com/v1/fullyqualifieddomain");
Console.WriteLine(json);

Resources

NuGetAPIVerve.API.FullyQualifiedDomainThe published C# / .NET client, versioned and signed.GitHubapiverve/fullyqualifieddomain-apiSource, issues and the examples this page is built from.ReferenceFully Qualified Domain API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/fullyqualifieddomainnpm apiverve-fullyqualifieddomainPyPI

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Go — GET /v1/fullyqualifieddomain

No SDK to install — this is a plain HTTPS call to /v1/fullyqualifieddomain with your key in the x-api-key header. Swap in a real key and it runs as-is.

req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/fullyqualifieddomain", nil)
req.Header.Set("x-api-key", "YOUR_API_KEY")

res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))

Resources

Also published for

@apiverve/fullyqualifieddomainnpm apiverve-fullyqualifieddomainPyPI APIVerve.API.FullyQualifiedDomainNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from PHP — GET /v1/fullyqualifieddomain

No SDK to install — this is a plain HTTPS call to /v1/fullyqualifieddomain with your key in the x-api-key header. Swap in a real key and it runs as-is.

PHP

$ch = curl_init("https://api.apiverve.com/v1/fullyqualifieddomain");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-api-key: YOUR_API_KEY"]);

$response = curl_exec($ch);
echo $response;

Resources

Also published for

@apiverve/fullyqualifieddomainnpm apiverve-fullyqualifieddomainPyPI APIVerve.API.FullyQualifiedDomainNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Ruby — GET /v1/fullyqualifieddomain

No SDK to install — this is a plain HTTPS call to /v1/fullyqualifieddomain with your key in the x-api-key header. Swap in a real key and it runs as-is.

Ruby

require "net/http"

uri = URI("https://api.apiverve.com/v1/fullyqualifieddomain")
req = Net::HTTP::Get.new(uri)
req["x-api-key"] = "YOUR_API_KEY"

res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
puts res.body

Resources

Also published for

@apiverve/fullyqualifieddomainnpm apiverve-fullyqualifieddomainPyPI APIVerve.API.FullyQualifiedDomainNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

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Fully Qualified Domain API

Try it — live request, no key required

About the Fully Qualified Domain API

What people use it for

Ways to call it

Other ways to use Fully Qualified Domain

Questions.

Request parameters — GET /v1/fullyqualifieddomain

Required

Authentication

Response — GET /v1/fullyqualifieddomain

Response fields

Response headers

Errors

What a call costs — 2 credits per call

Call it from cURL — GET /v1/fullyqualifieddomain

Resources

Also published for

Call it from Node.js — GET /v1/fullyqualifieddomain

Resources

Also published for

Call it from Python — GET /v1/fullyqualifieddomain

Resources

Also published for

Call it from C# / .NET — GET /v1/fullyqualifieddomain

Resources

Also published for

Call it from Go — GET /v1/fullyqualifieddomain

Resources

Also published for

Call it from PHP — GET /v1/fullyqualifieddomain

Resources

Also published for

Call it from Ruby — GET /v1/fullyqualifieddomain

Resources

Also published for

Zero-code embed — one snippet, no backend

Changelog — Fully Qualified Domain API

Domain Data

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