# SiteCheck Web Intel – Reverse DNS PTR Lookup

> SiteCheck Web Intel – Reverse DNS PTR Lookup is a paid API for AI agents from api.webintel-api.workers.dev, paid per call via x402, $0.002/call, status unknown (last checked 2026-10-24).

Returns PTR (reverse DNS) records for an IPv4 address and validates whether each PTR hostname resolves back to the same IP via forward-confirmed reverse DNS (FCrDNS).

## Facts

- Endpoint: GET https://api.webintel-api.workers.dev/api/security/reverse-dns-ptr?utm_source=zero.xyz
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-24
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/sitecheck-web-intel-reverse-dns-ptr-lookup-1e0e7511
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_CpPP6IQq9QO75wxYGmMw5

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability sitecheck-web-intel-reverse-dns-ptr-lookup-1e0e7511
```

Example prompt: Can you do a reverse DNS PTR lookup for 8.8.8.8 and tell me if the PTR hostname(s) forward-confirm back to that same IP address?

## When to prefer this

Use this endpoint when you need to resolve the hostname(s) associated with an IPv4 address via reverse DNS (PTR records) and additionally want to validate forward-confirmed reverse DNS (FCrDNS). Ideal for email server reputation checks, network security investigations, IP attribution in threat intelligence, or infrastructure audits. Prefer this over generic WHOIS or geolocation tools when the specific question is about DNS PTR records and hostname verification.

## Known failure modes

- Invalid or malformed IPv4 address input returns an error
- IP address with no PTR record returns an empty or null PTR list (normal, not an error)
- DNS timeout or upstream resolver failure may result in incomplete results
- Private/reserved IP ranges may not have PTR records
- PTR name exists but A record lookup times out, resulting in unconfirmed FCrDNS status

## How this service works

Reverse DNS (PTR) names for an IPv4 address, and forward-confirmed reverse DNS: whether each PTR name resolves back (A record) to the same address. Up to 3 PTR names are checked. Many addresses have no PTR record; that is a normal answer.

## Output

Returns up to 3 PTR hostnames associated with the given IPv4 address, along with a forward-confirmed reverse DNS (FCrDNS) check for each: whether the PTR hostname's A record resolves back to the original IP. If no PTR record exists, the response indicates that clearly as a normal (non-error) result.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "ip"
     ],
     "properties": {
      "ip": {
       "type": "string",
       "description": "IPv4 address such as 8.8.8.8 (required)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/sitecheck-web-intel-reverse-dns-ptr-lookup-1e0e7511/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.webintel-api.workers.dev](https://www.zero.xyz/host/api.webintel-api.workers.dev/llms.txt)