# SiteCheck Web Intel – Open DNS Resolver Check (Port 53)

> SiteCheck Web Intel – Open DNS Resolver Check (Port 53) 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).

Reports whether Shodan's passive scan data shows TCP port 53 (DNS) open on a given IPv4 address, indicating potential open resolver exposure.

## Facts

- Endpoint: GET https://api.webintel-api.workers.dev/api/security/open-resolver-check?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-open-dns-resolver-check-port-53-47020fc5
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_t6-J8ppiHTiIAlB6cesKU

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-open-dns-resolver-check-port-53-47020fc5
```

Example prompt: Can you check whether Shodan's passive scan data shows TCP port 53 (DNS) open on the IP address 198.51.100.42?

## When to prefer this

Use this endpoint when you need a fast, passive check on whether a specific IPv4 address has been observed by Shodan with port 53 (DNS) open, without sending any active probe. Ideal for security audits, threat intelligence enrichment, and reconnaissance workflows where you want to avoid active scanning. Prefer this over active DNS probing tools when stealth or passivity is required, or when you want Shodan's historical perspective rather than a real-time network probe.

## Known failure modes

- Missing or invalid IP address returns a 400-level error
- IPv6 addresses are not supported (IPv4 only)
- Shodan may have stale or incomplete data for less-scanned IP ranges
- IP not in Shodan's dataset returns a negative/absent result, which should not be interpreted as definitively closed
- Rate limiting or payment failure may return 402 or 429 errors

## How this service works

Reports whether Shodan's pre-collected passive scan data shows TCP port 53 (DNS) open on an IPv4 address. It is a passive port fact only: it does not send a query, so it cannot say whether the server answers recursively for outside names. Absence means not seen, not closed.

## Output

Returns whether Shodan's passive scan records show TCP port 53 open on the specified IPv4 address. The result is a passive observation: a positive result means Shodan previously detected the port open; absence means it was not seen in Shodan's data, not that the port is definitively closed. No active probe is sent.

## 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-open-dns-resolver-check-port-53-47020fc5/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)