OnlineCyberTools MCP (280+ filterable tools)

network_reverse_dns

Resolve an IPv4 or IPv6 address to its hostname(s) using a reverse DNS (PTR) lookup.

Instructions

Reverse DNS Lookup (PTR / IP To Hostname). Run a live reverse-DNS (PTR) lookup that resolves an IPv4 or IPv6 address back to its hostname(s) via the in-addr.arpa / ip6.arpa zone. Use it to map an IP to a name; use network_dns_lookup for forward records (A/AAAA/MX/TXT from a hostname) and network_whois for registration/ownership data. Issues outbound DNS queries (preferably via a registered remote worker, with a local resolver fallback), so results vary as DNS changes. CAPTCHA-gated and rate-limited (anonymous 10/min, 60/hour, 200/day). Returns the resolved hostnames plus the PTR query that was issued.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "ip": "<ip>"
    },
    "name": "network_reverse_dns"
  }
}

Input Schema

Name	Required	Description	Default
`ip`	Yes	IPv4 or IPv6 address to resolve to a hostname; validated, no scheme/port/CIDR, e.g. 8.8.8.8 or 2001:4860:4860::8888.
`dnsServer`	No	Optional resolver IP to query; defaults to 8.8.8.8.	8.8.8.8
`worker_id`	No	Optional registered healthy worker peer ID. Omit to use the default master-server behavior.

Output Schema

Name	Required	Description
`success`	No	True on the local resolver path when the lookup completed.
`ip`	No	The IP address that was queried, echoed back.
`dnsServer`	No	The resolver IP that was used.
`hostnames`	No	Resolved hostnames; empty when the IP has no PTR record.
`ptrQuery`	No	The reverse-zone query issued, e.g. 8.8.8.8.in-addr.arpa or an ip6.arpa name.
`ipType`	No	IPv4 or IPv6, inferred from the input.
`timestamp`	No	ISO 8601 timestamp of the response.

Schema Changelog

Changes observed during successful MCP inspections.

Changed5 schema fields changedv0.5.1Jun 3, 2026

changedInput schema / additionalProperties
```
Previous value: -trueNew value: +false
```

addedInput schema / properties / dnsServer

Added value: +{
+  "default": "8.8.8.8",
+  "description": "Optional resolver IP to query; defaults to 8.8.8.8.",
+  "type": "string"
+}

addedInput schema / properties / ip

Added value: +{
+  "description": "IPv4 or IPv6 address to resolve to a hostname; validated, no scheme/port/CIDR, e.g. 8.8.8.8 or 2001:4860:4860::8888.",
+  "examples": [
+    "8.8.8.8"
+  ],
+  "type": "string"
+}

addedInput schema / required
```
Added value: +[
+  "ip"
+]
```

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "properties": {
+    "dnsServer": {
+      "description": "The resolver IP that was used.",
+      "type": "string"
+    },
+    "hostnames": {
+      "description": "Resolved hostnames; empty when the IP has no PTR record.",
+      "items": {
+        "properties": {
+          "name": {
+            "description": "Resolved hostname (PTR target).",
+            "type": "string"
+          },
+          "source": {
+            "description": "Resolution method, gethostbyaddr or dns_get_record.",
+            "type": "string"
+          },
+          "ttl": {
+            "description": "Record time-to-live in seconds; 3600 for gethostbyaddr results.",
+            "type": "integer"
+          }
+        },
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "ip": {
+      "description": "The IP address that was queried, echoed back.",
+      "type": "string"
+    },
+    "ipType": {
+      "description": "IPv4 or IPv6, inferred from the input.",
+      "type": "string"
+    },
+    "ptrQuery": {
+      "description": "The reverse-zone query issued, e.g. 8.8.8.8.in-addr.arpa or an ip6.arpa name.",
+      "type": "string"
+    },
+    "success": {
+      "description": "True on the local resolver path when the lookup completed.",
+      "type": "boolean"
+    },
+    "timestamp": {
+      "description": "ISO 8601 timestamp of the response.",
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

First observedv0.1.0May 31, 2026

TDQS

A3.8/5.0

Behavior1/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations set readOnlyHint: false, implying potential side effects, but the description describes a purely read-only operation (lookup). This is a direct contradiction between annotations and description, which misleads the agent about safety.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Description is front-loaded with title and type, and all sentences add value. It is concise yet comprehensive without being verbose, though could be slightly more structured.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the presence of output schema and annotations, the description covers usage, limitations (DNS changes, rate limits), security considerations (CAPTCHA, worker), and alternatives, providing complete context for agent decision.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so parameters are already well-documented. The description adds examples and validation hints but does not significantly enhance meaning beyond the schema. Baseline 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

Description clearly states it performs reverse DNS lookup (PTR/IP to hostname) and distinguishes it from forward DNS and WHOIS lookups. The verb 'resolve' and resource 'IP address' are specific, and the description explicitly names sibling tools for comparison.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly says when to use this tool (reverse DNS) and when not: 'use network_dns_lookup for forward records' and 'network_whois for registration/ownership data'. Provides clear context and alternatives.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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