# Reverse DNS PTR Lookup via NextDNS

> Reverse DNS PTR Lookup via NextDNS is a paid API for AI agents from ip.intel.rallylive.ca, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-11).

Performs a reverse DNS (PTR) lookup for an IPv4 address using NextDNS as the resolver, returning hostnames, TTL, response code, and forward-confirmed reverse DNS (FCrDNS) status.

## Facts

- Endpoint: GET https://ip.intel.rallylive.ca/ip/ptr/via/nextdns?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-11
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/reverse-dns-ptr-lookup-via-nextdns-6e2dbd01
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_AuasaJzsyJ63OMH-FwKw1

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 reverse-dns-ptr-lookup-via-nextdns-6e2dbd01
```

Example prompt: What's the reverse DNS hostname for 203.0.113.42 as seen by NextDNS, and does the PTR's A record point back to the same IP (forward-confirmed)?

## When to prefer this

Use this endpoint when you specifically want to see how NextDNS resolves PTR records — useful for comparing resolver behavior, detecting filtered or stale PTR answers, or validating FCrDNS for mail server deliverability from the NextDNS perspective. Prefer this over generic PTR lookups when resolver-specific behavior matters.

## Known failure modes

- IP has no PTR record (NXDOMAIN response)
- NextDNS filters or blocks the PTR query, returning SERVFAIL or empty
- PTR exists but A record does not point back (FCrDNS fails)
- Invalid or non-routable IPv4 address input
- Timeout or upstream NextDNS resolver unavailability
- Payment failure for the $0.01 USDC per-call fee

## How this service works

Reverse DNS (PTR) of an IPv4 address as answered by NextDNS: the hostname(s), TTL and response code, plus whether the PTR's forward A record points back (forward-confirmed reverse DNS). Compare resolvers for stale or filtered answers. $0.01 per lookup.

## Output

Returns the PTR hostname(s) associated with the IPv4 address as resolved by NextDNS, along with the DNS TTL, response code (e.g. NOERROR, NXDOMAIN), and a boolean or flag indicating whether the PTR record is forward-confirmed (the hostname's A record resolves back to the original IP).

## 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",
     "properties": {}
    }
   },
   "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/reverse-dns-ptr-lookup-via-nextdns-6e2dbd01/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from ip.intel.rallylive.ca](https://www.zero.xyz/host/ip.intel.rallylive.ca/llms.txt)