# DNS Reverse Lookup (PTR + Co-hosted Domains)

> DNS Reverse Lookup (PTR + Co-hosted Domains) is a paid API for AI agents from dns-intel-api-production.up.railway.app, paid per call via x402, $0.002/call, status unknown (last checked 2026-09-16).

Performs a reverse-DNS lookup for a given IP address, returning its PTR record plus a best-effort list of other domains hosted on the same IP.

## Facts

- Endpoint: POST https://dns-intel-api-production.up.railway.app/dns/reverse
- Price: $0.002/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-16
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/dns-reverse-lookup-ptr-co-hosted-domains-b965ee14
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_WrclDLnNF3Kr-eFqqyosJ

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 dns-reverse-lookup-ptr-co-hosted-domains-b965ee14 -d '<json body>'
```

Example prompt: Can you do a reverse DNS lookup on 104.21.45.12 and tell me what hostname it resolves to, plus any other domains that appear to be hosted on the same IP?

## When to prefer this

Use this endpoint when you need to identify the hostname associated with a raw IP address, or when investigating which domains share a server. Ideal for security investigations, OSINT research, threat intelligence enrichment, or network diagnostics. Prefer this over forward DNS lookups when you start with an IP and need to work backwards to domain names. The co-hosted domain feature makes it more powerful than a plain PTR lookup for infrastructure mapping.

## Known failure modes

- IP has no PTR record configured — returns empty or null PTR field
- No co-hosted domains found — returns empty list (not an error, just no data)
- Invalid IP format provided — likely returns a validation error
- Private/RFC1918 IP address provided — no meaningful PTR record available
- Rate limiting or upstream DNS resolver failure — may return error or timeout
- IPv6 addresses may have limited co-hosted domain data

## How this service works

Reverse-DNS lookup for an IP: PTR record plus a best-effort list of other domains hosted on the same IP.

## Output

Returns the PTR (reverse DNS) record for the given IP — typically a hostname like 'one.one.one.one' — along with a best-effort list of other domain names found to be hosted on the same IP address, useful for identifying shared infrastructure or co-located services.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "ip": {
   "type": "string",
   "description": "IPv4 or IPv6 address to reverse-resolve, e.g. '1.1.1.1'."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/dns-reverse-lookup-ptr-co-hosted-domains-b965ee14/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from dns-intel-api-production.up.railway.app](https://www.zero.xyz/host/dns-intel-api-production.up.railway.app/llms.txt)