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Reverse DNS (PTR) Lookup

reverse_dns
Read-onlyIdempotent

Resolve the PTR (reverse DNS) record for an IPv4 or IPv6 address and verify forward-confirmed reverse DNS (FCrDNS) by checking that the PTR hostname resolves back to the same IP. Infers the hosting provider from PTR naming patterns. Use this to validate mail-server rDNS or identify a single IP's host. Use asn_lookup instead for network/BGP ownership of the IP. Read-only; requires no API key; rate-limited. Returns the PTR hostname, FCrDNS pass/fail, and a provider guess.

Input Schema

NameRequiredDescriptionDefault
ipYesIP address to reverse-resolve, IPv4 or IPv6 (e.g., '8.8.8.8' or '2001:4860:4860::8888'). Must be an IP, not a hostname.

Output Schema

NameRequiredDescriptionDefault
kpisNoKey metrics as label/value pairs
gradeNoLetter grade (A+ to F) when the tool grades the target
scoreNo0-100 score when the tool scores the target
issuesNoDetected problems, severity-rated
statusYesOverall verdict, e.g. 'good' | 'warning' | 'bad' | 'info' | 'unknown'
actionsNoRecommended next actions, most important first
summaryNoOne-paragraph interpretation of the result
receiptsNoSigned observation receipts behind this result, one per lookup: when, from where and under which rules version DechoNet observed it. Each url shows the record and checks its Ed25519 signature.
reportUrlYesHuman-facing interactive report for this exact lookup on dechonet.com
observationNoHow much was actually observed and when. A partial observation means some checks did not answer: missing parts are not verified, never clean.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • addedOutput schema / properties / receipts
      Added value: +{
      +  "description": "Signed observation receipts behind this result, one per lookup: when, from where and under which rules version DechoNet observed it. Each url shows the record and checks its Ed25519 signature.",
      +  "items": {
      +    "properties": {
      +      "id": {
      +        "type": "string"
      +      },
      +      "tool": {
      +        "type": "string"
      +      },
      +      "url": {
      +        "type": "string"
      +      }
      +    },
      +    "required": [
      +      "tool",
      +      "id",
      +      "url"
      +    ],
      +    "type": "object"
      +  },
      +  "type": "array"
      +}
  2. Changed1 schema field changed
    • addedOutput schema / properties / observation
      Added value: +{
      +  "description": "How much was actually observed and when. A partial observation means some checks did not answer: missing parts are not verified, never clean.",
      +  "properties": {
      +    "ageMinutes": {
      +      "type": [
      +        "number",
      +        "null"
      +      ]
      +    },
      +    "cached": {
      +      "type": "boolean"
      +    },
      +    "observedAt": {
      +      "type": [
      +        "string",
      +        "null"
      +      ]
      +    },
      +    "state": {
      +      "enum": [
      +        "complete",
      +        "partial",
      +        "unknown"
      +      ],
      +      "type": "string"
      +    }
      +  },
      +  "type": "object"
      +}
  3. First observed

TDQS

A4.5/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description still adds non-obvious operational context: no API key required and that the call is rate-limited, plus what FCrDNS actually checks and that a provider guess is inferred. It stops short of stating the rate-limit magnitude or failure behavior when PTR is absent.

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

Conciseness5/5

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

Front-loaded with the primary action, then verification behavior, then routing guidance, then constraints and returns. Every sentence carries distinct information with no padding.

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?

An output schema already exists, so the brief return summary is a bonus rather than a requirement. The description covers purpose, alternatives, side effects, and operational constraints for a single-parameter lookup tool, leaving nothing an agent needs to invoke it correctly.

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 coverage is 100% and the single parameter is fully documented in the schema, including the IPv4/IPv6 example and the 'must be an IP, not a hostname' constraint. The description restates that both IP versions are accepted but adds no format or edge-case detail beyond the schema, so the baseline 3 applies.

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?

States a specific verb (resolve) and resource (PTR reverse DNS record) plus the extra FCrDNS verification behavior and provider inference. It explicitly positions itself against asn_lookup, so an agent can distinguish the two without reading schemas.

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?

Gives concrete use cases ('validate mail-server rDNS or identify a single IP's host') and names the alternative tool with the condition that selects it ('Use asn_lookup instead for network/BGP ownership'). No exclusion is left to inference.

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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